Dissertations / Theses on the topic 'Colour systems'

Dielectric elastomers are electroactive polymers, which change size and shape in response to an electrical field. Dielectric elastomer actuators (DEAs) are highly promising new technologies in optical applications such as tuneable optical lenses, diffraction gratings and active camouflage. This thesis aims to develop a new approach to create a strain actuated compliant colour changing device that is controlled using DEAs as they offer stretchability, low weight, high efficiency, low cost and the possibility for miniaturisation. Conventional DEAs use transparent elastomeric materials with no significant colour change with strain. Conversely, liquid crystal materials are known to display dynamic colour changing behaviour, thereby making them good candidate materials. The thesis examines both the potential for colour changing soft actuators and the upcoming challenges in this field as well as the key concepts around liquid crystals that exhibit colour change. An initial approach was aimed at creating colour changes using dielectric elastomer actuators that drove a masked positioner. This method showed colour change since the mask changes the colour visualisation. The second approach used polymer dispersed liquid crystals, such as a nematic liquid crystal within a reactive silicone resin. The immiscibility of these compounds resulted in a dispersion of the liquid crystal droplets in the silicone matrix. However, the optical properties could not be controlled through mechanical deformation alone and the alignment of resulting LC droplets in the PDLC films was sensitive to the substrate used to perform the actuation. The next approach used reactive cholesteric liquid crystals (CLC) instead. A thin film coating process was preferred to carefully control the film's thickness by stretching. In free standing films a planar cholesteric alignment was obtained with mesogens aligned parallel to the substrate and colour was achieved based on the selective reflection of light. A transfer print technique was introduced to combine CLC coatings with elastomeric substrates that can be stretched. However, no colour change was achieved in response to mechanical deformation primarily due to the modulus and strength mismatch between the thin film and the elastomeric susbstrate material. Finally, lightly crosslinked liquid crystal elastomers using a combination of reactive and non-reactive liquid crystals were produced that were compatible with elastomer substrate materials. In free standing films planar cholesteric alignment was obtained with mesogens aligned parallel to the substrate. Successfully a reversible colour change based on selective reflection of light was achieved in response to a mechanical deformation.

The main purpose of this research is to study the colour characterisation of digital display systems. Three distinct models for characterisation (GOG, PLCC and PLVC) are evaluated and compared and for two of these models (GOG and PLCC) two different sets of linearisation samples (either colour-ramps or grey-ramp samples) are used to perform the linearisation. To evaluate these models’ colorimetric measurements are made for 20 different display devices and colour characterization performance is reported as the main measure. Characterisation performance is calculated using several sets of samples including the widely used Macbeth ColorChecker chart and two new charts called Chart4 and Matlab60 (one of which was based on a method previously published by Cheung and Westland and another was based on a new method). A key aspect of this work is that all 256 levels of intensity were measured for the colour-ramps and for the grey-ramp linearisation samples for each of the 20 displays to allow subsampling of these data to explore the effect of the number of linearisation samples on characterisation performance. When the number of linearisation samples used was small (less than 10) the GOG model sometimes resulted in the smallest characterisation colour differences. However, for the PLCC and PLVC models performance tended to increase with the number of linearization samples and both of these models outperformed GOG with more 10 linearisation samples. For the PLCC model, better performance was usually obtained using the grey-ramp linearisation samples rather than using the colour-ramps linearization samples. It was possible, for each of the 20 displays, to reach average ab values that are less than 1.5 (ab <1.5, 90%) or ab < 1.0 (75%); however, the model that yields the best performance is difficult to ascertain in advance (a good strategy would be to evaluate all five models and select the one that performs best for the characterisation of any particular display). However, in the majority of cases, lowest colour differences (ab) were obtained using the PLCC model and all 256 of the grey-ramp samples for linearisation. This work has compared the performance of five different models using a large number of displays and has allowed a number of recommendations to be made about display characterisation. Although the majority of the work in this thesis was based on stationary displays the effect of motion on characterization performance was also explored. This is important since moving images are now commonplace in many applications. The results showed that a moving background has a small, but statistically significant, effect on the colour of patches.

Diabetes Mellitus (DM) has become one of the most important metabolic diseases that reduces one’s quality of life and doubles the risk of early death. Amongst the major complications linked to DM, diabetic retinopathy (DR) leads to gradual loss of vision and blindness. DR is now the second cause of certifiable blindness among the working age adults in the UK. The lifetime costs to the UK government are calculated to be up to £327,000 per person, with almost 50% of these costs being attributed to loss of productivity caused by visual impairment and blindness. The UK is one of the leading countries in the implementation of DR screening programmes. The latter rely heavily on fundus imaging and grading using trained experts and subsequent referral to hospital for further clinical examination and evaluation depending on the grade of retinopathy. It is now known that subtle, structural changes in the retina that are linked to diabetes can precede detectable vascular changes. The former can affect one’s colour vision and this offers the potential of using changes in chromatic sensitivity as an early biomarker of retinal disease. The first part of this thesis focuses on measuring chromatic sensitivity using the colour assessment and diagnosis (CAD) test in diabetic subjects with varying degrees of retinopathy. The severity of colour vision loss is graded in comparison to other factors that are normally linked to diabetes, such as the type, grade, control methods and duration. The results of this study reveal losses of both red/green and yellow/blue chromatic sensitivity in patients with diabetes, but the correlation with factors, normally associated with high risk of diabetes is low. The results from this study do, however, show that the magnitude of chromatic sensitivity losses correlates with the severity of diabetic retinopathy. The second, related study examines the effectiveness of intravitreal injection of a dexamethasone implant (Ozurdex) in patients with diabetic macular oedema (DMO) in stabilising and reducing loss of visual function and in particular the reduction in chromatic sensitivity up to 24 weeks. This treatment demonstrated efficacy in the treatment of chronic DMO and DMO which is resistant to anti-VEGF treatment. The results show that intravitreal treatment with Ozurdex causes improvement is visual acuity, central retinal thickness and significant improvement in red/green chromatic sensitivity.

Colour mixing is fundamental to learning to paint. Students in visual art classes in secondary schools face problems in manipulating paint and discriminating colour. The kinds of base paints to be presented to students could be an important factor in learning about colour relationships and pigments. The purpose of this study was to determine whether Year 7 students generating colour mixes with paint using a triad of magenta, cyan and yellow were able to mix and discriminate more colours than if they used a triad of red(scarlet red), blue (ultramarine light) and yellow (lemon yellow) which is a base triad commonly used in schools. The Weddell Colour Discrimination Test was developed for use in this study which was a test that involved colour mixing with paint. The study used quasi-experimental designs for both a pilot study and a main study. Results indicated a significant difference in the ability to mix paint advantage of groups that used cyan , magenta and yellow. Implications for the use of particular colour triads in art classrooms and methods of teaching colour theory have emerged from this study. The Weddell Colour Discrimination test instrument developed in this study could be useful as both a diagnostic tool and a teaching tool as well as a data gathering method for further research.

The main purpose of this research project was to implement a combination of computer graphics and processing to generate displays that will aid in the visualization of the colour rendering properties of a range of light sources, including the new generation of high-output LEDs (light emitting diodes) that are becoming widely adopted in general lighting service. The CIE (International Commission on Illumination) has developed a colour appearance model CIECAM02 for use in colour imaging and colour management, and this model is utilized in this work. This thesis describes the design and construction of a computer-based model that can be used as a research tool for the simulation and demonstration of the colour rendering properties of various artificial light sources. It is a comprehensive study of the colour models and measurement procedures currently in use in the lighting industry, as recommended by the CIE. This research project focused on the display of a set of surface colour patches as if they were illuminated by a specific light source, and the simultaneous display of two such sets to demonstrate the surface colour differences arising from the use of the two different light sources. A VIS (virtual imaging system) has been developed to display the colour properties of a series of test colour samples under different light sources. This thesis describes the computer models developed for the representation and display of surface colours in general, and colour rendering in particular. The designed system computes and displays the colour of each sample from a knowledge of the light-source spectrum and the spectral reflectance of each surface. It can simultaneously display the colours resulting from illumination by two different sources. In addition, the system computes the colour appearance differences for two sets of colours using the CIECAM02 colour appearance model. Subjective and objective tests were taken to validate the computed results. The VIS has been designed and implemented. It also has been tested by 21 observers and we believe that it will be a powerful research tool for the lighting industry, especially in relation to colour rendering.

This thesis describes a quantitative experimental investigation into instantaneous colour constancy in humans. Colour constancy may be defined as the ability of the visual system to maintain a constant colour percept of a surface despite varying conditions of illumination. Instantaneous, in this context, refers to effects which happen very rapidly with the change of illumination, rather than those which may be due to long term adaptation of the photoreceptors. The results of experiments are discussed in the context of current computational models of colour constancy. Experiments on subjects with damage to the cerebral cortex are described. These highlight the different uses of chromatic signals within the cerebral cortex and provide evidence for location of the neural substrates which mediate instantaneous colour constancy. The introductory chapter describes briefly the visual system, in the first section, with particular reference to the processing of colour. The second section discusses the psychophysics of human colour vision and the third presents a summary of computational models of colour constancy described in the literature. Chapter two describes the dynamic colour matching technique developed for this investigation. This technique has the advantage of quantifying the level of constancy achieved, whilst maintaining a constant state of adaptation. The C index is defined as a measure of constancy, with 0 representing no constancy and 1 perfect constancy. Calibration procedures for the computer monitor and the necessary transformations to accurately simulate illuminant reflectance combinations are also described. Light scattered within the eye and its effect on colour constancy are discussed. Chapter three is concerned with the effects of altering the illuminant conditions on instantaneous colour constancy. The size of the illuminant shift is varied. Artificial illuminants are compared with those of the Plankian locus. The effects of overall illuminance and the luminance contrast between target and surround are investigated. Chapter four considers the spatial structure of the visual scene. Simple uniform surrounds are compared with those which have a more complex spatiochromatic structure (Mondrians). The effects of varying the test target size and shape are investigated. The decrease in constancy as a black border is placed between test target and surround is measured. Chapter five describes experiments on four subjects with damage to the cerebral cortex. Chromatic discrimination thresholds are investigated for three subjects with achromatopsia as are the contribution of both sighted and blind hemifields to constancy for a subject with hemianopia. Contrary to the predictions of many of the current computational models, using unnatural illuminants has no substantial effect on the C index, nor does the size of the illuminant shift or the luminance contrast between experimental target and surround. The complexity of the surrounding field does not effect constancy. These findings are similar to those from chromatic induction experiments reported in the literature. However, the effect of a black annulus is found to have different spatial parameters that those reported from experiments on chromatic induction, suggesting that a different mechanism may be involved. The three achromatopsics can be shown to exhibit instantaneous colour constancy. However the blind hemifield of the hemianope does not contribute. This suggests that the fusiform gyrus is not the human homologue of V4 and that the primary visual cortex is necessary for instantaneous colour constancy.

Museums and the performing arts have very specific lighting requirements, not only in the technical aspects of their presentation, but also in regard to the communication and interpretation of artistic concepts. Thus, the design intent might have many different perspectives whereas the idea of being “neutral” is more complex to define. One of the critical aspects for the visual experience of art is colour, a subjective experience that can be conceptually approached from many perspectives, from science to the artistic realm.  This study starts by setting a theoretical framework in colour human vision, colour theory and colourimetry; and how this can be applied to lighting design concepts for exhibitions. The experimental part of this work explores some of the opportunities of complex LED colour mix systems in working with fine colour tuning and metamers. This investigation focusses on both the creation of the light stimuli and on how these lighting conditions can influence the perception and interpretation of a painting. In spite of its subjectivity, the perception of the art is contextualized with the colour theory background provided, the quantitative measurements performed and the results of an online survey. Additionally, the artist is interviewed in an attempt to gather views from the origin of the artwork to the viewer interpretation. This work might be useful to those with interest in the opportunities that quality LED technology, specifically colour mixing, offer for lighting design in exhibition and theatre environment. In fact, the complexity of exhibition lighting provides a perfect environment for research and experimentation, where improving the viewer experience is becoming an essential factor for museology.

In this master thesis, a model-based video coding algorithm has been developed that uses input from a colour and depth camera, such as the Microsoft Kinect. Using a model-based representation of a video has several advantages over the commonly used block-based approach, used by the H.264 standard. For example, videos can be rendered in 3D, be viewed from alternative views, and have objects inserted into them for augmented reality and user interaction. This master thesis demonstrates a very efficient way of encoding the geometry of a scene. The results of the proposed algorithm show that it can reach very low bitrates with comparable results to the H.264 standard.
I detta examensarbete har en modellbaserad videokodningsalgoritm utvecklats som använder data från en djup- och färgkamera, exempelvis Microsoft Kinect. Det finns flera fördelar med en modellbaserad representation av en video över den mer vanligt förekommande blockbaserade varianten, vilket används av bland annat H.264. Några exempel är möjligheten att rendera videon i 3D samt från alternativa vyer, placera in objekt i videon samt möjlighet för användaren att interagera med scenen. Detta examensarbete påvisar en väldigt effektiv metod för komprimering av scengeometri. Resultaten av den presenterade algoritmen visar att möjligheten att uppnå väldigt låg bithastighet med jämförelsebara resultat med H.264-standarden.

Purpose WCAG is a set of guidelines to assist in developing websites accessible for everyone, for example people with colour vision deficiency (CVD). However, there are few guidelines relevant for CVD and with increasing dependant on websites the importance of accessibility on these websites increases as well. The purpose of the research study is therefore to investigate the impact the relevant guidelines for CVD in WCAG 2.1 has on Swedish health care websites and what the consequences are for people who live with CVD. Method An initial literature study was conducted to gain knowledge of previous findings and also evaluate the best approach for the research study. The research study is based on a qualitative approach to gain a deep understanding of the area and to gain insight into the feelings and experiences of the people affected. The methods used to gain the necessary knowledge are an evaluation of 1177.se and e-tjanster.1177.se also observations and interviews around these two websites. Findings The results show that WCAG 2.1 has a positive impact on Swedish health care websites, as well as on users with CVD. From evaluations, interviews and observations it is concluded that 1177.se and e-tjanster.1177.se are easy to perceive for people with CVD. Implications This research study was limited to the mobile version of the websites. However, the results could be different if the research was conducted on the desktop version due to the different structure of the websites and the inclusion of a cursor on desktop. The evaluation could have been affected by the sampling of pages while the interviews and observations should not have been. Limitations The research study was limited to Swedish health care website 1177.se and its subdomain etjanster. 1177.se. Further it was decided to evaluate the mobile version of these websites, although the elements should look similar on desktop and mobile. While not the initial intention, due to over representation of red-green CVD the study was also limited to people with red-green CVD. Also, the experience of browsing the web on a mobile device was considered to reduce the variables for frustrations. Further research For further research, another selection of WCAG guidelines could be considered to evaluate etjanster. 1177.se since the results shows that 1177.se’s and e-tjanster.1177.se's weaknesses seems to be in the structure of the website. A study researching the “blue-yellow colour blindness” compared to websites could contribute with new, relevant knowledge as well.

Paper coatings or coating colours are high solidssuspensions that are applied to paper to improve chieflyprintability and optical properties. A paper coatingsuspension, including pigments, binders and thickeners, is acomplex system which must be understood if the end-useproperties of paper are to be improved. Some of the importantissues that need to be addressed are the mechanisms ofmigration of latices in a drying film, the influence ofthickener on the overall consolidation and the behaviour ofpaper coatings under compression.U nderstanding theconsolidation of paper coatings is essential as the aggregatestructures formed at this stage largely determine theperformance of the paper coating.Similarly, the forming ofpaper itself from pulp fibres requires a detailed understandingof the consolidation and dewatering process.

In this thesis several approaches have been used in order tostudy the consolidation of paper coatings before and afterapplication to substrates. The techniques utilised arerheometry, centrifugation with NMR-imaging, scanning electronmicroscopy (SEM) and atomic force microscopy (AFM).Furthermore, investigations of the compressional rheology offibre systems has indicated that stepped pressure filtrationcan be a useful tool in the study of fibre dewatering.

The primary findings presented in this thesis can besummarised as follows. Studies of the compressive yield stressand rheological properties of ground calcium carbonate (GCC)suspensions indicate that the addition of a commonly usedthickener can cause flocculation, most likely of a depletiontype, which leads to more compact structures during dewatering.When applied to substrates, migration and film formation ofbinder latices in the presence of calcium carbonate pigmentsand CMC thickeners occurs concurrently and collectively. Thisis shown to influence the consolidation of the top layer of thecoating to a great extent. It was found that CMC retards themigration of latices and that ethyl(hydroxyethyl)cellulose(EHEC) adsorbs to latex and creates a composite material uponlocal film formation. The composite retains an internalhoneycomb structure in the film, that is revealed by mapping ofelastic variations using AFM phase imaging.

For fibre systems, the novel method of stepped pressurefiltration has been applied to study the compressional rheologyof pulp suspensions, and the effect of added surfactantsinvestigated. The technique is shown to be a promising tool forthe study of structure-dewatering relationships in fibresuspensions.

This thesis has investigated how the design process used by a textile printmaker practitioner requires further modification when the sun, uncontrollable by nature, is used to activate thermochromic leuco dyes, a dynamic surface variable. In the context of the use of the sun as the dynamic activator, the investigation is focussed on design applications of sun-screening textiles for both indoor and outdoor use. The work has been divided into two categories: the use of solar technology as a direct heater and as an indirect heat source using photovoltaic solar cells to power heat circuitry. The research has resulted in a set of recommended guidelines for textile printmaker practitioners for use when working with textile designs to create dynamic effects with thermochromic dyes, moving light and shadow imageries, in some cases utilising heat circuits activated using photovoltaics. The effect of the individual components of the design process is to allow creation of both dynamic imageries on the textile surface and ‘an extended imagery’, which at times may co-exist within two or three-dimensional space. This thesis, additionally, discusses the ability of the textile designer to achieve an intended aesthetic outcome, when working with an uncontrollable parameter, such as the sun, in comparison with the ‘traditional’ textile print design process.

This thesis presents an investigation into some of the structural colours that are produced in nature. There are many animals and plants that produce structural colour, with a particularly high structural colour diversity in insects. Of the species that exhibit structural colours, three species are the subjects for investigation of this thesis. Those comprise a group of beetles from South-East Asia, Torynorrhina flammea, a buttery, Parides sesostris and a fruit, Margaritaria nobilis, both from South American rainforests. The structures that produce the vivid colours of these species were analysed using electron microscopy. This information aided the design and creation of three inorganic, synthetic replicas of the natural structures. The fruit of Margaritaria nobilis was structurally analysed, yielding the discovery of a novel multilayer fibre. These fibres were cylindrical in design and were found to be layered together producing the epidermis of the fruit. The multilayer structure produced a vivid blue colour appearance, which is believed to offer a selective advantage because the colour deceives birds into thinking that the fruit contains nutritious flesh. This selective advantage earns M. nobilis the label of mimetic fruit. The structure found within the M. nobilis fruit epidermis inspired the synthesis of a structure which comprises single cylindrical multilayer fibres. The synthetic fibres were manufactured from elastic materials which allow the structure to be deformed under strain and, therefore, a change in colour can be observed. As the structure was stretched, this made the layers get thinner and, therefore, the colour of the fibre blue-shifted. The fibre was able to be stretched to over twice its original length which yields a shift in peak reflected wavelength of over 200 nm. Four beetles from the Torynorrhina flammea species were investigated with the aim of replicating the nanostructures responsible for their colour appearance. The initial interest in the beetles came from their strikingly vivid colour appearances. The structure responsible for the vivid colours in all four of the subspecies is a multilayer with high structural order and over 100 laminae. Both of these attributes contribute to the saturation of the colours exhibited. The multilayer was found to be intersected by an array of rods, the long axis of which is orthogonal to the surface. The rods are believed to be the cause of an interesting diffraction phenomenon exhibited by the beetles. Using imaging scatterometry, the structure was found to diffract the colour produced by the multilayers into an annulus around a specularly reflected white spot. This inspired the synthesis of a multilayer permeated with an array of holes with the aim of replicating a system that could reproduce the annular pattern of colour reflection. The initial synthesised system comprised a quarter-wave stack with a perfectly ordered hexagonal array of holes permeating the surface orthogonally. The sample displayed the scattering characteristics of a hexagonal array, and the reflection spectra of the multilayer stack. When disordered hexagonal arrays were milled into the structure with a focussed ion beam, the scattering pattern started to show more of the green colour from the multilayer and less of the ordered scattering pattern. The highly disordered, synthesised structure displayed no hexagonal scattering pattern, but instead it showed a highly scattered bluish-green colouration. One sample was created by directly mapping out the array of holes using an image of the original array from one of the beetle samples. This sample was expected the same annular diffraction pattern as the beetles, however, the sample instead exhibited the same scattering pattern as the highly disordered array. Some structurally coloured systems in nature have more than one light scattering structure, all of which contribute to the overall colour of the system. For complicated systems such as this, it is necessary to devise a technique to characterise the individual scattering structures separately. One such species that displays a complex, multicomponent system is Parides sesostris. The male of the species displays bright green patches on the dorsal side of the forewings which are made up of thousands of green wing scales. These green scales contain a 3D gyroid poly-crystal at centre with a membrane layer surrounding the underside of each scale and a scattering structure on top. Using focussed ion beam milling techniques allowed the individual characterisation of each of these structures. The gyroid poly-crystal was found to reflect not green but blue wavelengths. This led to the discovery by another group [1] that the scales contain at least one type of fluorophore. The removal of the membrane structure and some of the gyroid poly-crystal from the base of the scale resulted in the change of the overall scale structure from green to cyan. This suggests that the membrane maybe a significant source of fluorescence. Computational modelling, without fluorescence, suggests that the addition of the membrane layer to the gyroid does not shift the band-gap wavelengths; however, the overall reflection intensity does increase. The scattering structure on the top side of each scale is comprised a bi-grating which sits on top of the 3D gyroid structure. The long periodicity of the bi-grating protrudes above the surface, resulting in the very top layer of the scale to be a mono-grating. This whole structure decreases the angular-dependence of the colour by efficiently scattering the incident light into the gyroid and also scattering the reflected light from the gyroid, resulting in a double-scattering. FIB-milling was used to isolate the scattering part of the structure. Analysis of this component of the structure revealed that it was not a source of the green colour itself; however, it did show the characteristic scattering pattern of a mono-grating. The small periodicity of the bi-grating did not produce a scattering pattern since the periodicity is too small to produce optical diffraction at normal incidence. To characterise the effect of the fluorophores, the whole scale structure was photo-bleached using ultra-violet radiation for two months with the aim of destroying the fluorophores contained within the structure. The expected result occurred which was the blue-shifting of the peak reflected wavelengths. However, it could not be confirmed whether or not the photo-bleaching reduced the physical size of the light scattering structures which would, in theory, result in a blue-shift of the peak reflected wavelengths. The male P. sesostris green wing scales were also the subject for investigation for trying to make inorganic replicas of the gyroid-polycrystal. A surface sol-gel coating process was utilised to coat the green wing scales with titania. This coating process was performed using a few different methods. Half of the samples were coated with TiO2 and the other half with tin-doped TiO2. Half of each of these samples had their surfaces dendritically amplified before the coating processes and the other half were left untreated. The samples were coated with 25 surface sol-gel (SSG) cycles of each treatment at a time. After each 25 cycle treatment the samples were optically characterised. The total number of cycles applied to the samples at the end was 150. The addition of layers of titania resulted in a general red-shift that was higher for the tin-doped titania samples than for the titania samples. Another general trend found was that the samples that had their surfaces dendritically amplified, produced a lower red-shift in peak wavelength. This was contrary to the hypothesis that the amplification process was supposed to aid the SSG coating process and, therefore, increases the red-shift in peak wavelength.

Hoy en día, los sistemas de imagen basados en cámaras CCD son ampliamente utilizados en numerosos campos, en particular, en el campo de la imagen científica debido a su alta resolución, alta eficiencia cuántica, amplia respuesta espectral, aceptable razón señal-ruido, linealidad, fidelidad geométrica, rápida respuesta, tamaño reducido y durabilidad.
A pesar de esto, si se quiere utilizar una cámara CCD como instrumento de medida, se debe tener en cuenta que las cámaras CCD no son detectores perfectos, si no que presentan diversas fuentes de ruido inherentes a su funcionamiento que alteran los niveles digitales correspondientes a cada píxel, distorsionan la imagen real adquirida de forma desconocida y reducen la precisión radiométrica, la calidad de la imagen y su resolución.
Dos de las relativamente recientes aplicaciones de los sistemas de imagen basados en cámaras CCD son la medida del color, consistente, básicamente, en estimar los valores triestímulo XYZ asociados a una muestra de color a partir de los niveles digitales de respuesta del sistema, y la reconstrucción espectral, consistente en estimar el espectro de reflectancia de una muestra de color a partir de los niveles digitales correspondientes de la respuesta del sistema.
No obstante, para llevar a cabo medidas de color o reconstrucciones espectrales mediante este tipo de dispositivos es necesario realizar una caracterización o calibración previa de estos sistemas de imagen, con el objetivo de determinar la transformación que define la correspondencia entre las repuestas digitales del sistema y, por un lado, un espacio de color independiente del dispositivo, como el XYZ o el CIELAB, ya que las respuestas digitales del sistema, incluso las señales de salida RGB de un sistema de imagen tricromático, no se corresponden con los valores triestímulo independientes del dispositivo basados en el observador colorimétrico estándar de la CIE, o bien, por otro lado, el espacio de reflectancias espectrales, respectivamente.
Los métodos de caracterización colorimétrica se pueden dividir en dos categorías generales: los métodos basados en las sensibilidades espectrales del sistema, algunos de los cuales normalmente sólo se aplican a configuraciones colorimétricas, es decir, con tres canales de adquisición, debido a su creciente complejidad al incrementar el numero de canales de adquisición, y los métodos basados en una carta de colores. Los métodos basados en las sensibilidades espectrales del sistema requieren el conocimiento de dichas sensibilidades para cada canal de adquisición, las cuales deben haberse determinado previamente mediante la caracterización espectral del sistema.
En cuanto a los métodos de reconstrucción espectral, su principal objetivo es reconstruir el espectro de reflectancia, transmitancia o radiancia de una muestra de color a partir de las correspondientes respuestas digitales del sistema de imagen. Estos métodos se aplican habitualmente a configuraciones multiespectrales ya que los modelos lineales de espectros de reflectancia utilizados requieren como mínimo cuatro canales de adquisición para ser capaces de estimar espectros de reflectancia reales.
Para que un sistema de imagen basado en una cámara CCD pueda ser utilizado como un instrumento de medida con elevada resolución espacial, de forma que la totalidad del área de detección del sistema sea útil para medir, es necesario corregir la no-uniformidad espacial de la respuesta del sistema. Con este propósito se utilizan básicamente dos tipos de técnicas. En primer lugar, las técnicas basadas en la escena se fundamentan en aplicar un algoritmo a la imagen original con el objetivo de obtener una mejora considerable en la calidad de la imagen a expensas de la precisión radiométrica. En segundo lugar, las técnicas de corrección de campo uniforme o de la nouniformidad espacial se basan en la calibración del sistema mediante dos imágenes: una imagen oscura y una imagen de campo uniforme, que se combinan linealmente con la imagen original. Este segundo tipo de técnicas permiten llevar a cabo medidas radiométricas precisas utilizando una cámara CCD. En la literatura se pueden encontrar diversas variantes de estas técnicas de corrección de campo uniforme o de la no-uniformidad espacial. La más general de estas variantes permite llevar a cabo la corrección de la no-uniformidad espacial de la respuesta del sistema de forma independiente de la nouniformidad de la iluminación de la escena, lo que resulta particularmente útil en varias condiciones de medida como, por ejemplo, en el caso de imágenes de objetos radiantes.
La utilización de un sistema de imagen basado en una cámara CCD para medidas de color o reconstrucciones espectrales con elevada resolución espacial requiere la aplicación del segundo tipo de técnicas de corrección de la no-uniformidad espacial. En este trabajo se presentan la metodología experimental desarrollada para corregir las fuentes de ruido inherentes a un sistema de imagen basado en una cámara CCD, y la optimización de un algoritmo de corrección de la no-uniformidad espacial para obtener la mejor corrección posible de la no-uniformidad espacial.
El principal objetivo de este trabajo es desarrollar un sistema de imagen multispectral para la medida del color. En este trabajo se presentan el diseño y desarrollo de un prototipo de sistema multiespectral en el rango visible del espectro y su minuciosa caracterización y análisis. Con este propósito se utiliza un sistema de imagen basado en una cámara CCD, por lo que es necesario llevar a cabo, en primer lugar, la corrección del ruido de la respuesta del sistema, concretamente la corrección de la no-uniformidad espacial, y, en segundo lugar, la caracterización o calibración del sistema mencionada anteriormente, para poder obtener los valores triestímulo XYZ y/o los espectros de reflectancia, respectivamente, a partir de las respuestas digitales del sistema. En este trabajo se utilizan dos sistemas de imagen basados en una cámara CCD: uno basado en una cámara CCD 10-bits color, y uno basado en una cámara CCD 12-bits monocromática refrigerada. De este último sistema se consideran dos configuraciones: una configuración colorimétrica con 3 canales de adquisición, y una configuración multiespectral con 7 canales de adquisición. La caracterización espectral se lleva a cabo sólo para la configuración colorimétrica de ambos sistemas con el objetivo de aplicar el método de caracterización colorimétrica basado en las sensibilidades espectrales del sistema. Por otro lado, se aplican diversos métodos de medida del color y reconstrucción espectral a las dos configuraciones del sistema basado en una cámara CCD 12-bits monocromática refrigerada y se comparan utilizando todas las combinaciones posibles de las cartas GretagMacbeth ColorChecker Color Rendition (CCCR) y GretagMacbeth ColorChecker DC (CCDC) como conjuntos de entrenamiento y prueba del sistema, con el objetivo de determinar los métodos más adecuados para cada configuración, es decir, los métodos que permiten conseguir la mejor precisión tanto en la medida del color como en la reconstrucción espectral para cada configuración. Al mismo tiempo se compara también el comportamiento de ambas configuraciones en términos de precisión de la medida del color y de la reconstrucción espectral.
El hecho de que las sensibilidades espectrales de la mayoría de las cámaras CCD color (3 canales de adquisición) no verifiquen la condición de Luther, es decir, no sean transformaciones lineales de las funciones de igualación del color de la CIE, limita seriamente las aplicaciones colorimétricas de los sistemas basados en cámaras CCD color, dando lugar a valores triestímulo estimados dependientes del iluminante. Esta propiedad de las sensibilidades espectrales motiva el uso de sistemas multiespectrales ya que la única forma de asegurar una igualación del color para todos los observadores y bajo cambios en la iluminación es consiguiendo la igualación espectral. El método más directo para obtener información espectral de las muestras medidas es incrementar el muestreo por encima de los tres canales de adquisición tradicionales mediante filtros de banda estrecha, lo que se conoce como un sistema de imagen multiespectral. Los campos de aplicación de los sistemas de
imagen multiespectral se ha incrementado enormemente en los últimos años, fundamentalmente debido a la posibilidad que ofrecen de estimar con precisión el espectro de reflectancia en cada píxel y, a partir de éste, los valores triestímulo XYZ, evitando del metamerismo.
El sistema de imagen multiespectral diseñado y desarrollado en este trabajo doctoral para la medida del color está compuesto por un cámara CCD 12-bits monocromática refrigerada, una rueda de filtros motorizada y controlada vía software con un conjunto de filtros interferenciales de banda estrecha y un objetivo de focal variable. En coherencia con los resultados obtenidos en trabajos previos [Vilaseca et al., 2006] en la región NIR del espectro y extrapolándolos al rango visible, se utiliza un conjunto de siete filtros interferenciales de banda estrecha cubriendo por completo el rango visible del espectro, con la misma FWHM y longitudes de onda de pico equidistantes. Cada filtro constituye un canal de adquisición del sistema multiespectral, que corresponde a la configuración multiespectral del sistema de imagen antes mencionado.
El primer paso antes de poder utilizar un sistema de imagen basado en una cámara CCD como instrumento de medida con elevada resolución espacial es llevar a cabo la corrección de las diferentes fuentes de ruido inherentes a su funcionamiento, y muy concretamente la corrección de la nouniformidad espacial de la respuesta del sensor. Con esta objetivo, en este trabajo se ha desarrollado una metodología experimental para la corrección de dichas fuentes de ruido, y se ha llevado a cabo la optimización de un algoritmo de corrección de la no-uniformidad espacial.
A lo largo de este trabajo doctoral se han realizado también diversos análisis con el objetivo de mejorar la precisión de la medida del color y de la reconstrucción espectral utilizando sistemas de imagen basados en cámaras CCD.
En primer lugar, considerando los conceptos básicos aplicados en imagen de alto rango dinámico (HDRI) para obtener una representación del contenido visual de una escena real independiente del dispositivo, se propone un balance de adaptación luminosa para incrementar el rango dinámico del sistema mediante la captura de imágenes con diferentes tiempos de exposición obteniendo así niveles digitales útiles para todos los píxeles. La aplicación de este balance de adaptación luminosa permite determinar el color en todos los píxeles de la imagen, incrementando así el rango dinámico del sistema [Pujol et al., 2006].
En segundo lugar, se analiza la influencia del número de muestras del conjunto de entrenamiento en la precisión de la medida del color y la reconstrucción espectral con el objetivo de determinar si existe alguna relación entre la precisión y el tamaño del conjunto de entrenamiento. La precisión del sistema mejora incrementando el tamaño del conjunto de entrenamiento hasta alrededor de 110 muestras, y pasa a ser independientes del conjunto de entrenamiento utilizado para conjuntos de entrenamiento con un número de muestras igual o superior a 110.
A continuación, se analizan la medida del color y la reconstrucción espectral llevadas a cabo utilizando las dos configuraciones del sistema, colorimétrica y multiespectral, en función de las gamas de colores medidas, es decir, conjuntos de muestras de color agrupadas en función de su tono, con el objetivo de determinar si estas configuraciones son especialmente sensibles a algunos tonos y/o a otras propiedades del color. En primer lugar se analizan las tendencias generales utilizando la carta CCDC como conjunto de entrenamiento y prueba y, en segundo lugar, se utilizan las 1269 muestras de color del Munsell Book of Color - Matte Collection, clasificadas en 10 tonos Munsell y cada uno de éstos en 4 sub-tonos, para analizar la influencia de la homogeneidad en tono del conjunto de entrenamiento.
Se comprueba que la homogeneidad en tono del conjunto de entrenamiento permite mejorar de forma significativa la precisión del sistema tanto en la medida del color como en la reconstrucción espectral [de Lasarte et al., 2008 - 2]. Por otro lado, se utilizan tres combinaciones de conjuntos de entrenamiento y prueba de las muestras Munsell para variar el grado de homogeneidad en tono del conjunto de entrenamiento, obteniéndose los mejores resultados para los conjuntos de entrenamiento más homogéneos en tono.
Los resultados obtenidos se analizan también en función de las características del color de las muestras medidas como son las coordenadas CIELAB, y las coordenadas Munsell de tono, 'value' y croma. No se observa ningún tipo de correlación entre la precisión del sistema y las coordenadas CIELAB, mientras que la precisión del sistema tiende a empeorar para muestras con valores de la coordenada Munsell Value V > 7 - 8.
Se analiza también la influencia del iluminante mediante la comparación de los resultados obtenidos utilizando dos iluminantes: una lámpara incandescente y un simulador D65. Los mejores resultados se obtienen para la combinación configuración multiespectral del sistema y simulador D65 como iluminante.
Seguidamente, la precisión de la medida del color y la reconstrucción espectral se analiza en función de los espectros de reflectancia de las muestras de color medidas para determinar si existe algún tipo de correlación entre ambos. Este estudio se lleva a cabo utilizando la configuración multiespectral del sistema y el iluminante D65, la carta CCDC y las muestras Munsell como conjuntos de entrenamiento y prueba. La precisión de la medida del color y la reconstrucción espectral se analizan en función de, por un lado, el área bajo la curva (AUC) de los espectros de reflectancia y, por otro lado, la suavidad de los espectros de reflectancia mediante su Transformada Discreta de Fourier (DFT), que se utiliza frecuentemente en análisis de espectros para determinar la suavidad de las curvas. Respecto al análisis del AUC, la precisión del sistema en la medida del color tiende a mejorar para muestras con AUC de sus espectros de reflectancia mayores, aunque no se puede establecer ninguna relación directa entre ambas. Esta tendencia no se observa en términos de la precisión de la reconstrucción espectral. Una mayor precisión en la reconstrucción espectral se asocia con frecuencia a espectros de reflectancia suaves, aunque tampoco se puede establecer ninguna correlación entre ambos. En cuanto al análisis de la DFT, la precisión en la medida del color parece ser independiente de la forma y/o la suavidad de los espectros de reflectancia, mientras que la mayor precisión en la reconstrucción espectral se asocia con frecuencia a un espectro de reflectancia suave, aunque no se puede establecer una correlación general entre ambas. Una vez completado el minucioso análisis del sistema multiespectral desarrollado y establecidas sus limitaciones en cuanto a precisión en la medida del color y la reconstrucción espectral, la siguiente etapa es determinar si algún otro número y/o combinación de filtros interferenciales disponibles comercialmente permitiría mejorar, al menos teóricamente, la precisión del sistema multiespectral. Con este propósito se lleva a cabo un estudio de simulación de un sistema multiespectral óptimo para la medida del color y la reconstrucción espectral. Este estudio se realiza considerando la respuesta espectral del la cámara CCD 12-bits refrigerada monocromática utilizada y una base de datos de filtros disponibles comercialmente seleccionados entre las bases de datos de Edmund Optics, OptoSigma y CVI. Se observa que la precisión del sistema se mejora al incrementar el número de filtros, aunque esta mejora está limitada y tiende a ser insignificante para un número de filtros superior a 8. Los filtros óptimos tienden a compensar la respuesta espectral de la cámara CCD sobre todo el rango visible pero teniendo en cuenta el inconveniente que suponen el desconocer las transmitancias reales de los filtros (las simulaciones dependen en gran medida de las transmitancias reales de los filtros, que no siempre se pueden simular fácilmente a partir de las especificaciones de los proveedores), la selección de un conjunto de filtros interferenciales con posiciones de pico equidistantes cubriendo todo el rango visible, iguales FWHM que permiten un ligero solapamiento entre ellos, y la mayor transmitancia posible, como se ha hecho en este trabajo, constituye una opción más que aceptable para obtener un sistema multiespectral útil.
Finalmente, se comprueba la aplicabilidad del sistema multiespectral desarrollado utilizando, no sólo cartas de color estandarizadas, como son las CCDC, CCCR y las muestras Munsell, sino utilizando también un conjunto de 56 muestras textiles agrupadas en 28 parejas, que fueron especialmente fabricadas para comprobar la aplicabilidad de las fórmulas de diferencia de color, y el simulador D65 como iluminante. Se analizan diferentes combinaciones de conjuntos de entrenamiento y prueba. Los mejores resultados se obtienen, en promedio, utilizando conjuntos de entrenamiento homogéneos en tono y llevando a cabo una clasificación previa de las muestras textiles en tonos. Además, se comprueba la capacidad del sistema multiespectral desarrollado de detectar pequeñas diferencias, tanto en color como en el espectro de reflectancia, entre muestras reales, resultando así ser útil para aplicaciones que requieran discriminación, aunque se obtiene una escasa precisión en la determinación de las diferencias tanto de color como en las reflectancias espectrales entre los pares de muestras textiles considerados.
Nowadays, imaging systems based on CCD cameras are widely used in several fields and, particularly in the field of scientific image, due to its high resolution, high quantum efficiency, wide spectral response, acceptable signal-to-noise ratio, linearity, geometric fidelity, fast response, small size and durability.
In spite of this, if a CCD camera is wanted to be used as a measuring instrument, one must bear in mind that CCD cameras are not perfect detectors, but there are various noise sources inherent to their performance that alter the digital levels corresponding to each pixel, distort the real image acquired in an unknown manner, and diminish the radiometric accuracy, the image quality and the resolution.
Two of the relatively recent applications of the imaging systems based on CCD cameras are colour measurement and spectral reconstruction. Colour measurement basically consists of estimating the XYZ tristimulus values associated to a colour sample from the system's response digital levels, whereas spectral reconstruction consists of estimating the reflectance spectrum of a colour sample from its corresponding system's response digital levels.
Nevertheless, performing colour measurements and/or spectral reconstructions using this kind of devices requires a previous characterization or calibration of the imaging system. On one hand, colour measurement requires to determine the transformation that defines the correspondence between system's digital responses and a colour space independent of the device, such as the XYZ or the CIELAB. This is due to the fact that system's digital responses, even the RGB output signals for a trichromatic imaging system, do not correspond with the device independent tristimulus values based on the CIE standard colorimetric observer. On the other hand, spectral reconstruction requires to determine the transformation that defines the correspondence between system's digital responses and the reflectance spectra space.
Methods for colorimetric characterization can be divided in two general categories: methods based on spectral sensitivities, some of which are usually only applied to colorimetric configurations of imaging systems, i.e. with three acquisition channels, due to its growing complexity when the number of acquisition channels is increased, and methods based on a colour sample chart. Methods based on spectral sensitivities require the knowledge of the system's spectral sensitivities for each acquisition channel, which can be previously determined through the spectral characterization of the imaging system.
Regarding the methods for spectral reconstruction, their main objective is to reconstruct the reflectance, transmittance or radiance spectra of a colour sample from the corresponding digital responses of the imaging system. These methods are usually applied to multispectral configurations since the linear models of reflectance spectrum used require at least four acquisition channels to be able to estimate real reflectance spectra.
In order an imaging system based on a CCD camera can be used as a measuring instrument with high spatial resolution, so that the whole system's detection area is useful for measuring, it is mandatory to correct the spatial non-uniformity of the system's response. Basically two kinds of techniques are used with this purpose. Firstly, the scene-based techniques are based on applying an algorithm to the original or raw image in order to obtain a considerable improvement in image quality at the expense of radiometric accuracy. Secondly, the flat-field correction or spatial non-uniformity correction techniques are based on calibrating the detector by means of two images: a dark image and a uniform field or flat-field image, which are linearly combined with the original or raw image (image to be corrected). These second type techniques allow to use a CCD camera to perform accurate radiometric measurements. Several variants of these flat-field correction or spatial non-uniformity correction techniques can be found in literature. The most general of these variants allow the correction of the spatial non-uniformity of the system's response independently of the spatial non-uniformity of the scene illumination, which is quite useful in several measurement imaging conditions, such as in the case of images corresponding to self-radiating objects.
Using an imaging system based on a CCD camera for high spatial resolution colour measurement and/or spectral reconstruction requires applying one of the second type techniques for the spatial non-uniformity correction. In this work, the experimental methodology developed to correct the inherent noise sources of an imaging system based on a CCD camera, and the optimization of a spatial non-uniformity correction algorithm to obtain the best spatial non-uniformity correction possible are presented.
The main aim of this work is to develop a multispectral imaging system for colour measurement and spectral reconstruction. The design and development of a prototype of multispectral imaging system in the visible range of the spectrum and its thorough characterization and analysis is presented in this work. For this purpose, an imaging system based on a CCD camera is used. Therefore, in order to be able to perform accurate colour measurements and/or spectral reconstructions with high spatial resolution it will be necessary to carry out, firstly, the noise correction of the system's response, particularly the correction of the spatial non-uniformity, and secondly, the previously mentioned characterization or calibration of the imaging system to be able to obtain the XYZ tristimulus values and/or the reflectance spectra, respectively, from the system's digital responses.
Two imaging systems based on a CCD camera are used in this work: an imaging system based on a colour 10-bits CCD camera, and an imaging system based on a monochrome 12-bits cooled CCD camera. Two configuration of this last imaging system are considered: a colorimetric configuration with 3 acquisition channels, and a multispectral configuration with 7 acquisition channels. The spectral characterization is carried out only for the colorimetric configuration of the previously mentioned two imaging systems, in order to be able to apply the method for colorimetric characterization based on the spectral sensitivities of the imaging system.
Different methods for colour measurement and spectral reconstruction are applied to the two configurations of the imaging system based on a monochrome 12-bits cooled CCD camera, and compared using all possible combinations of the GretagMacbeth ColorChecker Color Rendition chart (CCCR) and the GretagMacbeth ColorChecker DC chart (CCDC) as training and test sets, in order to determine the most suitable methods for each configuration, i.e., the methods that allow to achieve the best accuracy of both colour measurement and spectral reconstruction for each configuration. At the same time, the performance of the two configurations is also compared in terms of both accuracy of colour measurement and accuracy of spectral reconstruction.
The fact that the spectral sensitivities of most of the commercial colour CCD cameras (3 acquisition channels) do not verify the Luther condition, i.e., are not linear transformations of the CIE colour matching functions, seriously limitates the colorimetric applications of the imaging systems based on colour CCD cameras, giving rise to estimated tristimulus values dependent of the illuminant. This property of the spectral sensitivities motivates the use of multispectral imaging systems, since the only way to assure a colour matching for all observers and under changes in illumination is achieving a spectral matching. The most direct method to obtain spectral information of the measured samples is to increase the sampling over the three traditional acquisition channels by means of narrowband filters, which is known as a multispectral imaging system. The application fields of the multispectral imaging systems have increased enormously in last years, fundamentally due to the possibility that offer of estimating accurately the reflectance spectrum at each pixel and, from it, the XYZ tristimulus values avoiding metamerism.
The multispectral imaging system designed and developed in this work comprises a monochrome 12-bits cooled CCD camera, a motorized filter wheel controlled via software with a set of narrowband filters, and an objective lens of variable focal length. A set of seven narrowband interference filters covering the whole visible range of the spectrum, with equal FWHM and equidistant central wavelengths, are used following the results obtained in previous works in the NIR region of the spectrum, and extrapolating them to the visible range. Each filter constitutes an acquisition channel of the multispectral imaging system, which corresponds to the multispectral configuration of the imaging system mentioned previously.
The first stage before an imaging system based on a CCD camera can be used as a measuring instrument with high spatial resolution is to carry out the correction of the different noise sources inherent to the CCD's performance and, especially, the correction of the spatial non-uniformity of the sensor's response. With this aim, the experimental methodology to correct these noise sources has been developed and a linear algorithm for the spatial non-uniformity correction of the system's response has been optimized.
Several analyses have also been carried out throughout this work in order to improve the accuracy of the colour measurement and the spectral reconstruction performed using imaging systems based on CCD cameras.
Firstly, considering the basic concepts applied in high dynamic range imaging (HDRI) to obtain a device independent representation of the visual content of a real scene, a luminance adaptation model is proposed to increase the dynamic range of the imaging system by taking images at different exposure times in order to obtain useful digital levels for all the pixels. The application of this luminance adaptation model allows to measure colour at each pixel of the image, increasing the dynamic range of the imaging system by this way.
Secondly, the influence of the number of samples of the training set on the accuracy of colour measurement and spectral reconstruction is analyzed in order to determine if there exists a relationship between the accuracy of colour measurement and spectral reconstruction, and the size of the training set. Accuracy of system's performance improves by increasing the size of the training set up to 110 colour samples approximately, and becomes independent of the training set used for training sets having a number of colour samples greater or equal to 110.
Next, colour measurement and spectral reconstruction performed using both the colorimetric and the multispectral configurations of the imaging system are analyzed depending on the colour ranges measured, i.e. sets of colour samples grouped by their hue property, with the aim of determining if these configurations are especially sensitive to some hues and/or some other colour properties. Firstly, general tendencies are analyzed using the CCDC chart as training and test sets, and secondly, the 1269 colour patches of the Munsell Book of Color - Matte Collection, classified in 10 Munsell hues and each one of these hues in 4 sub-hues, are used to analyze the influence of homogeneity in hue of the training set on system's performance.
Homogeneity in hue of the training set is proved to allow improving meaningfully accuracy of system's performance in terms of both colour measurement and spectral reconstruction. On the other hand, three combinations of training and test sets of Munsell's colour patches are used in order to vary the degree of homogeneity in hue of the training set. Best results are obtained using the most homogeneous in hue training sets.
Furthermore, results obtained are also analyzed depending on the colour characteristics of samples measured such as the CIELAB coordinates, and the Munsell hue, value and chroma coordinates. No correlation is observed between accuracy of system's performance and the CIELAB coordinates, whereas accuracy of system's performance tends to get worse for samples having Munsell Values V > 7 - 8.
The influence of the illuminant used is also analyzed by comparing results obtained using two illuminants: an incandescent lamp illuminant, which is the one used so far, and a D65 simulator illuminant.
Then, accuracy of colour measurement and spectral reconstruction is analyzed depending on the reflectance spectra of the colour samples measured, in order to determine if there exists any kind of correlation between them. This study is performed using the best proved combination of system's configuration and illuminant, which is multispectral configuration and D65 simulator illuminant, and the CCDC chart and the Munsell's colour patches as training and test sets. Accuracy of colour measurement and spectral reconstruction is analyzed depending on, on one hand, the Area Under the Curve (AUC) of reflectance spectra and, on the other hand, on the smoothness of the reflectance spectra by means of their Discrete Fourier Transform (DFT), which is usually used in spectrum analysis to determine the smoothness of curves. Considering the AUC analysis, accuracy of colour measurement tends to improve for the colour samples with higher AUCs of their reflectance spectra, whereas this tendency is not observed for the accuracy of spectral reconstruction. However, any direct relationship cannot be established either between the accuracy of colour measurement and the AUC of the reflectance spectra of colour samples. Considering the DFT analysis, accuracy of colour measurement seems to be independent of the shape and/or the smoothness of the reflectance spectra, whereas the best accuracy of spectral reconstruction is frequently associated to a smooth reflectance spectrum, although any general correlation cannot be established between them.
Once thoroughly analyzed the multispectral imaging system developed, and established its limitations in terms of accuracy of colour measurement and spectral reconstruction, next stage is determining if any other number and/or combination of commercially available interference filters would allow to improve, at least theoretically, the accuracy of the multispectral imaging system in terms of colour measurement and spectral reconstruction. For this purpose, a simulation study of an optimum multispectral imaging system for colour measurement and spectral reconstruction is presented. This study is performed considering the spectral response of the monochrome 12-bits cooled CCD camera used and a database of commercially available interference filters selected among the databases of Edmund Optics, OptoSigma and CVI. Accuracy of system's performance is improved in terms of accuracy of both colour measurement and spectral reconstruction with an increasing number of interference filters. Nevertheless, this improvement is limited and tends to be insignificant for more than 8 filters. Optimum filters tend to make up for the spectral response of the CCD camera over the whole visible range but considering the drawback the unknown real spectral transmittances of filters supposes (simulations depend greatly on the real spectral transmittances of filters, which not always can be easily simulated from the specifications provided by suppliers), the selection of a set of interference filters having equidistant peak positions covering the whole visible range, equal FWHMs that allow a slight overlapping between them, and the higher transmittance possible, as it was done in this work, constitutes an acceptable option to obtain a worthy multispectral imaging system.
Finally, the applicability of the multispectral imaging system developed is tested not only using standardized colour charts, such as the CCCR, CCDC, and the Munsell's colour patches used so far, but also using real samples, such as a set of 56 textile samples grouped in 28 pairs, which were made specifically to test the applicability of colour difference formulas, and the D65 simulator illuminant. Different combinations of training and test sets are analyzed. Best results are obtained, in average, using training sets homogeneous in hue and carrying out a previous hue classification of the textile samples used as test set. Moreover, the multispectral imaging system developed is proved to be able to detect slight differences both in colour and in reflectance spectra between real samples, making it useful for applications that require discrimination, although a quite low accuracy of system's performance is obtained in detecting both the colour differences and the spectral differences between pairs of textile samples.

Tooth whitening is becoming popular in the world today due to peoples' increased awareness of their cosmetic appearance. Tooth whitening is usually achieved either by the physical removal of stain using abrasives or by chemically reducing it with the help of bleaching agents. Product evaluations have been carried out by different investigators and manufacturers to assess the whitening efficacy of different products. Techniques employed in product testing should be standard, reliable, precise and accurate so that meaningful comparisons may be carried out. Tooth whitening and stain has been conventionally assessed by means of visual techniques with the help of shade guides and stain indices. Emergence of instrumental techniques has reduced the subjectivity of conventional techniques and has also provided more standardised methods and parameters for product evaluation. The present clinical studies investigate two novel digital techniques for their suitability to assess and quantify tooth colour and stain. A White Light Digital Imaging system was tested for its capability to assess tooth colour and stain. A novel . Fluorescence Imaging system (Quantitative Light Induced Fluorescence system) was investigated for its suitability to quantify stain. Clinical implementation of a novel whiteness index was also tested for its ability to measure tooth colour and stain. The digital techniques and the parameters were investigated for their ability to assess tooth colour and stain with the help of clinical trials through product evaluation and comparison. The proposed Whiteness Index was concluded as a more appropriate index, amongst the colour parameters, to measure differences in tooth whiteness. The White Light Digital Imaging system was efficient in measuring tooth colour and diffused stain. QLF was concluded as more suitable in detecting and quantifying well defined stain areas on the tooth surface.

The role of redox reactions in the formation of aroma volatiles, colour and other non-volatiles in the Maillard Reaction was investigated. The electrochemical properties of individual reactants and Maillard model mixtures were monitored via ORP (oxidation-reduction potential) and oxygen electrodes. All models exhibited unique electrochemical activities represented by their corresponding ORP profiles. Investigation into the redox potentials of several model systems demonstrated that the increased negative value of a redox potential is not necessarily correlated with its browning potential. An optimal redox potential range, where browning is favoured, was found to represent a balance between carbonyl and hydroxyl moieties in the structure. Adjustment of this redox potential by introducing reducing or oxidizing species can shift this balance resulting in modifications in browning capacities. However, it was concluded that there is a clear relationship between browning ability and reducing capacity of the model systems. Furthermore, a novel oxidative pyrolysis technique was developed to study the role of oxidative environment on the product distribution during pyrolysis and to investigate the mechanism of formation of non-volatiles through 13C and 15N-label incorporation. Application of this technique to glucoselglycine model system have indicated that most non-volatile Maillard reaction products can arise from glucose oxidation intermediates such as glucosone, gluconic acid and deoxyglucosones. To study the specific role of redox reactions in the formation of non-volatiles, a post-pyrolytic derivatization technique was developed and optimized. Several non-volatile end products were identified and mechanistically confirmed to involve oxidation and reduction reactions for their formation, such as lactones, hydroxylated benzenes and hydroxylated pyrazine. The latter was identified and confirmed to be generated via the dimerization of glycine and subsequent oxidation. In addition, the formation of different volatiles such as pyrazole, imidazole and oxazole was mechanistically confirmed to depend on redox reactions.

L'auto-organisation de nanoparticules métalliques dans un support est un moyen efficace et peu coûteux de produire des systèmes plasmoniques pouvant être utilisés pour des applications d'affichage couleur actif, de codage d'image et de sécurité. De tels systèmes nanocomposites doivent être synthétisés sous forme de films stables qui pourraient être enduits sur tout type de surface pour un traitement laser. Cette thèse de doctorat porte sur l 'auto - organisation induite par laser de couches minces nanocomposites d' argent et d 'oxyde de titane mésoporeux.Dans ce travail, nous étudions d'abord la synthèse de couches minces mésoporeuses de TiO2 à l'aide d'un processus hydrolytique, facile à mettre en œuvre, pour fournir des films cristallisés à partir de 100 ° C. sont rapportés dans ce travail. En outre, les mécanismes de croissance des nanocristaux dans les films mésoporeux de TiO2 sont étudiés sous la forme de mesures ellipsométriques mettant en évidence son effet sur la porosité et la cristallinité du film avec la température de recuit.La deuxième étude démontre la fabrication de différentes structures nanocomposites à l'aide de la technique de balayage laser femtoseconde, déclenchant la croissance et l'auto-organisation de nanoparticules d'argent à l'intérieur d'une matrice de titane amorphe poreuse donnant lieu à des couleurs dichroïques plasmoniques. Une recherche plus approfondie sur l'étude paramétrique de ces nanocomposites donne lieu à différentes nanostructures à deux régimes de vitesse de balayage différents, qui se forment à la surface et sont noyées en dessous en raison de l'excitation de la surface et des modes guidés. La flexibilité de cette technologie de marquage laser permet également de fabriquer des nanostructures hybrides composées de différents types de nanostructures adjacentes, entrelacées pour couvrir de grandes surfaces. Une extension de cette étude est conclue sur des substrats plastiques / flexibles pour encoder des images imprimées diffractives. Ici, les nanostructures de surface (LIPSS) sont formées en utilisant le contrôle de la polarisation du laser et donc de l'orientation du réseau, qui est utilisé pour coder des images de niveau de gris qui peuvent être observées dans les modes de diffraction.De plus, cette étude se conclut en produisant trois multiplexages d'images qui peuvent être observés dans trois modes sélectionnés d'observation sous lumière blanche en réflexion avec lumière non polarisée et transmission entre polariseurs pour deux angles de polarisation différents. Cela est dû au fait que la biréfringence et le dichroïsme du film peuvent être contrôlés pour produire des gammes de couleurs sans précédent pour le multiplexage. Un tel traitement laser intelligent sur des films minces nanocomposites donne lieu à des applications artistiques et de sécurité en codant différentes images jusqu'à trois sous la même zone
Self-organization of metallic nanoparticles in a medium is an efficient and a low-cost way to produce plasmonic systems that can be used for applications to active colour display, image encoding, and security. Such nanocomposite systems must be synthesized in form of stable films which could be coated on any kind of surface for laser processing. This doctoral thesis focuses on laser‐induced self‐organization of nanocomposite thin films of silver and mesoporous titania.In this work, we first investigate synthesizing mesoporous TiO2 thin films using hydrolytic process, which is easy to implement, to provide crystallized films starting at 100°C. First activation energies in mesoporous TiO2 films using Raman spectroscopy in combination with the phonon quantum confinement model are reported in this work. Further, growth mechanisms of nanocrystals in mesoporous TiO2 films are investigated in form of ellipsometric measurements highlighting its effect on film porosity and crystallinity with annealing temperature.The second study demonstrates fabrication of different nanocomposite structures using femtosecond laser scanning technique, triggering growth and self-organization of silver nanoparticles inside porous amorphous titania matrix giving rise to plasmonic dichroic colours. Further investigation on the parametric study of such nanocomposites gives rise to different nanostructures at two different scan speed regimes, which are formed at the surface and are embedded below due to excitation of surface and the guided modes. The flexibility of this laser-based marking technology also allows to fabricate hybrid nanostructures composed of different adjacent nanostructure types, interlaced to cover large areas. An extension of this study is concluded on plastic/flexible substrates to encode diffractive printed images. Here surface nanostructures (LIPSS) are formed by using the control of laser polarization and thus grating orientation, which is used to encode grey-level images that can be observed in diffraction modes.Further, this study is concluded by producing three image multiplexing which can be observed in three selected modes of observation under white light in reflection with non-polarized light and transmission between polarizers for two different polarization angles. This is due to the fact that the film birefringence and dichroism can be controlled to produce unprecedented colour gamuts for multiplexing. Such smart laser processing on nanocomposite thin films gives rise to artistic and security applications by encoding different images up to three under same area

The colour of guppies (Poecilia reticulata) evolves as a compromise between sexual selection (favouring conspicuousness) and natural selection (favouring crypsis). However, guppies live in a variety of habitats and with a variety of predators and consequently in a variety of selective environments. I investigated how habitat and predator's visual systems affect the evolution of colour. I used regressions to assess the importance of habitat features on the evolution of colour for 29 guppy populations. I then quantified the colour of guppies living in the presence and absence of two predators. The prawn predator is insensitive to orange light while the fish predator is insensitive to ultraviolet light. Habitat explained some variation in colour, but not in a consistent manner. Guppies living with the prawn were more orange and guppies living with the fish had more ultraviolet reflectance, providing evidence for the use of these aspects of colour as private signals.

The field of telehealth has developed rapidly in recent years. It provides medical support particularly to those who are living in remote areas and in emergency cases. Although developments in both technology and practice have been rapid, there are still many gaps in our knowledge with regard to the effective application of telehealth. This study investigated human colour perception in telehealth, specifically the colour red as one of the key symptoms when diagnosing different pathologies. The quality of medical images is safety critical when transmitting the symptoms of pathologies in telehealth, as distorted or degraded colours may result in errors. The study focused on the use of digital images in teleconsultation, particularly on images showing cellulitis (bacterial skin infection) and conjunctivitis (red eye) as case studies, as both of these pathologies involve the colour red in their diagnosis. The study proposed and tested the use of an image quality scale, which represented the level of image resolution; a red colour scale, which represented the intensity of redness in an image; and a confidence scale, which represented the levels of confidence that telehealth users had when judging the colour red. The research involved a series of experiments using hypothetico-deductive and formal hypothesis testing with two groups of participants, medical doctors and non-medical participants. The experiments were conducted in collaboration with the local National Health Service (NHS) Accident and Emergency (A&E) department at Aberdeen Royal Infirmary (ARI). Medical experts in ophthalmology and dermatology were also involved in selecting and verifying the relevant images. The study found that doctors and non-doctors were consistent in the majority of the experiments. The accuracy of the participants was demonstrably higher when using a colour scale with pictures, more so for the non-doctor group than the doctor group. It also found that the level of accuracy for both doctors and nondoctors was higher when using red colour scale of three divisions than when using a scale of five divisions. This result was supported by previous studies, which used telehealth for diagnosing extreme cases. The study also found that when the image quality was poor the participants had higher error rates and less consistency in their answers. The study found poor correlation between accuracy, confidence and time for both participant groups. The study found that most participants in both doctor and non-doctor groups had high confidence most of the time, whether the accuracy was high or low. It was also found that medical background or clinical experience had no effect on the accuracy level across the experiment sets. In some cases, doctors with no or little experience had higher accuracy than those with greater experience. This result may have significant implications for the feasibility of involving non-doctors in the management of telehealth systems, especially in tasks not requiring medical skills, such as colour classification. This has the potential to provide a considerable saving in resources and costs for healthcare providers. An auto-evaluation system was introduced, and proposed for further study, in order to improve the current telehealth diagnostic protocol and to avoid or prevent errors by making red colour classification more objective and accurate.

This two-part thesis focuses on biointerfaces of two different biological systems. It specifically examines the interplay of structure and functionality in these biointerfaces. Part one studies photo-bio-electrochemically active bacteria and the strong dependence of their electrical current generation on electrode structure and pigment organisation. Part two uncovers surprising design principles of photonic structures on flower petals and presents research tools to study disordered optical systems. Biophotovoltaics (BPV) is a newly described biophysical effect in which a biofilm of photosynthetic microorganisms associated with an anode produces electrical current that can be harvested and passed through an external circuit. In this thesis-part, an experimental set-up is presented to quantitatively measure photo-electric activity of cyanobacteria in BPVs. Using this set-up, a systematic study of anode morphologies reveals that large electrode surface areas enhance photocurrents by two orders of magnitude, identifying structuration as key design criterion for bioelectrochemical interfaces. Electrodes with micrometer-sized pores allow enhanced direct contact area with bacteria, but with tested cyanobacteria this did not result in a photocurrent increase, disproving recent speculations in the literature. Furthermore, a theoretic-mathematical framework is presented to estimate light-energy utilisation in biofilms. It is detailed how pigment concentration and distribution affects the light-level dependent saturation of electron harvesting biofilms. This study brings the theory together with experiments, such as genetic modification and photo-current measurements. Part two of this thesis approaches the interaction of light and biointerface structuration from a different angle. In a significant extension of the candidate’s MPhil project, it was discovered that the disorder in natural photonic structures can be an advantage rather than a limitation in biology. With biological image analysis, optics simulations and nano-manufacturing a new photonic effect is uncovered which is iridescent but surprisingly constant in chroma. In collaboration with plant scientists, it is shown that many flowers have co-evolved disordered surface structuration that generates this bee visible colouration.

Denna uppsats undersöker hur kvinnor och män i olika åldersgrupper förhåller sig till Flashapplikationer utifrån deras uppfattning om färg och form. Deltagarna som består av skolungdomar, nyexaminerade studenter och pensionärer har genom en enkät och en semistrukturerad intervjuform fått redogöra för sina intryck av Santa Marias, Eccos och Indiskas webbplatser.

Undersökningsdeltagarna identifierar Flashelementen genom deras rörelser. Deltagarna vill välja om de ska se animationer och andra applikationer skapade i Flash för att inte tappa koncentrationen från övrigt innehåll. Studenterna i undersökningen har en mer kritisk hållning till färgval, formgivning och användandet av Flash än övriga. Kvinnorna i undersökningen har en mer liberal hållning till färg och form än männen.

This essay explores how men and women in different age groups experiences Flashapplications, depending on their perception of colour and form. The participants, teenagers at a junior high school, students who just have finished their degree and senior citizens have by answering a form and by taking part in a semi structured interview been able to express their opinion of the following Scandinavian web pages: Santa Maria, Ecco and Indiska.

The participants identify the flash objects by their movements. The participants want to be able to choose weather or not to see the animations and other applications created in Flash, to avoid loosing focus on the other information the trademarks wants to express. The students have the most critical approach to colour, form and the use of Flash objects. The female participants have a more liberal approach to colour and form then the male participants.

An integrating approach, including knowledge about whole systems of processes, is essential in order to reach both development and environmental protection goals. In this thesis Geographical Information Systems (GIS) are suggested as a tool to realise such integrated models. The main hypothesis in this work is that several natural technical and social systems that share a time-space can be compared and analysed in a GIS. My first objective was to analyze how GIS can support research, planning, and, more specifically, bring a broad scattering of competence together in an interdisciplinary process. In this process GIS was ivestigated as a tool to achieve models that give us a better overview of a problem, a better understanding for the processes involved, aid in foreseeing conflicts between interests, find ecological limits and assist in choosing countermeasures and monitor the result of different programs. The second objective concerns the requirement that models should be comparable and possible to include in other models and that they can be communicated to planners, politicians and the public. For this reason the possibilities to communicate the result and model components of multidimensional and multi-temporal data are investigated. Four examples on the possibilities and problems when using GIS in interdisciplinary studies are presented. In the examples, water plays a central role as a component in questions about development, management and environmental impact. The first articles focus on non-point source pollutants as a problem under growing attention when the big industrial and municipal point sources are brought under control. To manage non-point source pollutants, detailed knowledge about local conditions is required to facilitate precise advices on land use. To estimate the flow of metals and N(itrogen) in an area it is important to identify the soil moisture. Soil moisture changes over time but also significantly in the landscape according to several factors. Here a method is presented that calculate soil moisture over large areas. Man as a hydrologie factor has to be assessed to also understand the relative importance of anthropogen processes. To offer a supplement to direct measurements and add anthropogen factors, a GIS model is presented that takes soil-type, topography, vegetation, land-use, agricultural drainage and relative position in the watershed into account. A method to analyse and visualise development over time and space in the same model is presented in the last empirical study. The development of agricultural drainage can be discussed as a product of several forces here analyzed together and visualized with help of colour coded "Hyper pixels" and maps. Finally a discussion concerning the physiological and psychological possibilities to communicate multidimensional phenomena with the help of pictures and maps is held. The main conclusions in this theses are that GIS offer the possibilities to develop distributed models, e.g., models that calculate effects from a vide range of factors in larger areas and with a much higher spatial resolution than has been possible earlier. GIS also offer a possibility to integrate and communicate information from different disciplines to scientists, decision makers and the public.

Diss. (sammanfattning) Umeå : Umeå universitet, 1993, härtill 6 uppsatser.

digitalisering@umu

SyAet med denna studie var a< förstå hur konsumenter i Sverige med olika könsroller och åldrarupplever elektroniska (e-) handelswebbsidor som =llförlitliga baserat på den visuella designen.SyAet besvarades genom a< undersöka färg- och typografins påverkan på upplevd =llförlitlighet före-handelswebbsidor, u=från konsumentens perspek=v.År 2021 används e-handeltjänster alltmer för a< köpa produkter. Företag kan numera nå ut =ll fleroch större målgrupper genom e-handel då företagets geografiska belägenhet inte längre äravgörande för kunden. EAersom e-handelsmarknaden växer och konkurrensen blir allt hårdare, ärdet vik=gt a< företagen är medvetna om dess visuella presenta=on på webbsidan för a< fåkonsumenternas =llit. Resultat av =digare studier visar a< färg och typografiska val är vik=ga faktorerför huruvida en webbsida upplevs =llförlitlig. Tidigare forskning visar även på hur olika kön och åldrarförhåller sig =ll internet och hur olika deras användningsmönster ter sig vad gäller teknologi.Denna studie uUördes med hjälp av en visuell innehållsanalys och en enkätundersökning. Resultatenfrån den visuella innehållsanalysen gav verktyg =ll a< skapa fik=va webbsidor med olika färg ochtypsni<, som vidare användes i enkätundersökningen. Totalt tolv e-handelswebbsidor skapades =llenkätundersökningen för a< utreda vilken färg samt typsni< som upplevs vara mest =llförlitlig.Studien indikerade jämna resultat mellan åldersgrupper samt könsroller vad gäller upplevelse av=llförlitlighet u=från färg- och typografival på e-handelswebbsidor. Resultatet visade tendenser =lla< den orangea samt gula webbdesignen upplevdes minst =llförlitliga enligt respondenterna i dennastudie. Något mer =llförlitliga upplevdes färgerna grön, blå, röd och rosa. Studien indikerade a<sanserif-typsni< ansågs något mer trovärdigt än seriff-typsni<.
The purpose of this study was to understand how credible consumers in Sweden with differentgender roles and ages perceived electronic (e-) commerce websites based on the visual design. Thepurpose was answered by examining the impact of colour and typography on perceived credibilityof e-commerce webpages from the consumers’ perspec=ve.In 2021, e-commerce services are increasingly being used to purchase products. Businesses cannowadays reach a much larger market through e-commerce, as the geographical loca=on of thecompany is not anymore cri=cal to customer availability. As the e-commerce market grows evenlarger, companies should be more aware of their visual presenta=on on the website to gainconsumer trust. Previous studies show that colour and typographic choices are important factors inwhether a webpage is perceived trustworthy. Previous research gives insight to how different genderroles and age groups relate to the internet and have different usage pa<erns.This study was carried out using a visual content analysis and a ques=onnaire. The results of thevisual content analysis gave the prerequisites for crea=on of the fic=onal webpage layouts withdifferent colours and typefaces that were further used in the ques=onnaire. A total of twelve ecommercewebpage were created for the ques=onnaire to inves=gate which colours and typefacesare experienced to be most credible.The study indicated even results between age groups and gender roles in terms of experience ofcredibility regarding colour and typography choices on e-commerce websites. The results showedtendencies that the orange as well as yellow webdesigns were the least credible according torespondents in this study. Green, blue, red, and pink were considered more credible than orangeand yellow designs. The study also indicated that sans serif typeface was considered slightly morecredible than serif typeface.

This thesis addresses the pose stabilization of a car-like vehicle using omnidirectional visual feedback. The presented method allows a vehicle to servo to a pre-learnt target pose based on feature bearing angle and range discrepancies between the vehicle's current view of the environment and that seen at the learnt location. The best example of such a task is the use of visual feedback for autonomous parallel-parking of an automobile. Much of the existing work in pose stabilization is highly theoretical in nature with few examples of implementations on 'real' vehicles, let alone vehicles representative of those found in industry. The work in this thesis develops a suitable test platform and implements vision-based pose stabilization techniques. Many of the existing techniques were found to fail due to vehicle steering and velocity loop dynamics, and more significantly, with steering input saturation. A technique which does cope with the characteristics of 'real' vehicles is to divide the task into predefined stages, essentially dividing the state space into sub-manifolds. For a car-like vehicle, the strategy used is to stabilize the vehicle to the line which has the correct orientation and contains the target location. Once on the line, the vehicle then servos to the desired pose. This strategy can accommodate velocity and steering loop dynamics, and input saturation. It can also allow the use of linear control techniques for system analysis and tuning of control gains. To perform pose stabilization, good estimates of vehicle pose are required. A simple, yet robust, method derived from the visual homing literature is to sum the range vectors to all the landmarks in the workspace and divide by the total number of landmarks--the Improved Average Landmark Vector. By subtracting the IALV at the target location from the currently calculated IALV, an estimate of vehicle pose is obtained. In this work, views of the world are provided by an omnidirectional camera, while a magnetic compass provides a reference direction. The landmarks used are red road cones which are segmented from the omnidirectional colour images using a pre-learnt, two-dimensional lookup table of their colour profile. Range to each landmark is estimated using a model of the optics of the system, based on a flat-Earth assumption. A linked-list based method is used to filter the landmarks over time. Complementary filtering techniques, which combine the vision data with vehicle odometry, are used to improve the quality of the measurements.

Radio networks can provide reliable communication for rural intelligent transportation systems (ITS). Engineers manually design these radio networks by selecting tower locations and equipment while meeting a series of constraints such as coverage, bandwidth, maximum delay, and redundancy, all while minimizing network cost. As network size and constraints grow, the design process can quickly become overwhelming. In this thesis we model the network design problem (NDP) as a generalized Steiner tree-star (GSTS) problem. Any solution to the minimum Steiner tree (MST) problem on a constructed GSTS graph will directly identify the tower locations and equipment needed to build the network at an optimal cost. The direct MST solution can only satisfy coverage constraints. Because the MST problem is known to be NP-hard, our research applies ant colony optimization (ACO) to find near-optimal MST solutions. Using ACO also allows us to meet bandwidth, maximum delay, and redundancy constraints. We verify that our approach finds near-optimal designs by comparing it against a 2-approximation algorithm in several different scenarios.

This research explores the differences between how game engine cameras and the human visual system (HVS) render colour. The study is motivated by a two part research question: will HVS colours or game camera colours be preferred when experiencing a virtual environment from a 1st-person perspective and how does light intensity relate to preference? While previous research defines perceptual processes which influence the interpretation of colour information this study advances the understanding of how these theories may be applied to 3D colour grading.When evaluating the two colour modes with a combination of quantitative data and qualitative reflections it was possible to establish a correlation between preference and light intensity, in the sense that HVS colours were preferred in high illumination and camera colours in low. The findings implicate that in order to be well received the colours of a virtual environment need to be adjusted according to illumination.

Theoretical part of the diploma thesis purveys information on drinking water and quality requirements, changes of drinking water quality during distribution and accumulation caused by disinfection, chemical processes, corrosion of constructional materials, incrusting solids, biofilms, nitrification of ammonia nitrogen, sediments in pipelines, elution of harmful matter. Attention was given to drinking water quality indicators which are associated with changes in drinking water distribution systems. In experimental part are studied changes of drinking water quality during distribution on the basis of selected drinking water quality indicators. There is specifically chemical oxygen demand, concentration of iron, manganese, ammonia ions, nitrites, nitrates, chloroform and chlorine. For periodical monitoring were selected suitable locality within the framework of Brno distribution system; for illustration were taken water samples from distribution systems of drinking water treatment plants Švařec, Vír, Štítary and Mostiště. For selected methods of analytical determination of above mentioned drinking water quality indicators are presented their characteristics. Obtained information on drinking water quality is mentioned in tabular and graphical form.

This research is focused on the development of colorimetric tools to improve the current colour management systems which are based on the specifications defined by the International Color Consortium (ICC) and can be only applied in a set of restricted working conditions.

This thesis describes the design and hardware implementation of a high speed multi-processor interface used in a colour graphics animation system. The design involves the use of Direct Memory Access to move data between the memories of the various CPUs constituting the Grads system. The system accommodates the various bus protocols, word sizes, and interrupt schemes of the different processors. An evaluation of the completed system is presented.

Multiple camera arrays are beginning to see more widespread use in a variety of different applications, be it for research purposes or for enhancing the view- ing experience in entertainment. However, when using multiple cameras the images produced are often not color consistent due to a variety of different rea- sons such as differences in lighting, chip-level differences e.t.c. To address this there exists a multitude of different color calibration algorithms. This paper ex- amines two different color calibration algorithms one targeted and one target- less. Both methods were implemented in Python using the libraries OpenCV, Matplotlib, and NumPy. Once the algorithms had been implemented, they were evaluated based on two metrics; color range homogeneity and color ac- curacy to target values. The targeted color calibration algorithm was more ef- fective improving the color accuracy to ground truth then the target-less color calibration algorithm, but the target-less algorithm deteriorated the color range homogeneity less than the targeted color calibration algorithm. After both methods where tested, an improvement of the targeted color calibration al- gorithm was attempted. The resulting images were then evaluated based on the same two criteria as before, the modified version of the targeted color cal- ibration algorithm performed better than the original targeted algorithm with respect to color range homogeneity while still maintaining a similar level of performance with respect to color accuracy to ground truth as before. Further- more, when the color range homogeneity of the modified targeted algorithm was compared with the color range homogeneity of the target-less algorithm. The performance of the modified targeted algorithm performed similarly to the target-less algorithm. Based on these results, it was concluded that the targeted color calibration was superior to the target-less algorithm.

The theory of stellar evolution and stellar structure relies on the observation of stars in di erent phases of their evolutionary cycle. The relation between observations and theory can be strengthened by obtaining observational data of a large sample of stars in a particular evolutionary phase. The search for Cephei stars, as conducted in this study, can contribute to the sample of known Cephei stars, where these interesting stars are massive non-supergiant early B-type stars, displaying pulsating behaviour which is not well understood. Stars tend to form in clusters where it can therefore be expected that young massive stars can be found in open clusters. For this reason two young southern open clusters were observed in order to search for B-type pulsating stars. The region of NGC 6204 and Hogg 22 was observed over a period of thirteen nights in Johnson B, V and I bands. NGC 6204 is believed to be the oldest cluster of the two at a distance of 0.8 kpc while the much younger Hogg 22 is more distant at 2.8 kpc. These two open clusters are located 6 arcminutes apart which made it possible to observe them simultaneously with a 12.8 12.8 arcminute eld of view. The observations were done with the newly installed 1600 telescope of the North-West University, South Africa. In order to do a variability search, periodic stars need to be identi ed from the cluster data, where a typical data set may contain thousands of scienti c images. In addition to the main motivation for this study, a pipeline was created in order to automate the photometry and data reduction processes. A Lomb-Scargle transform was applied to the stellar light curves in order to identify periodic sources. 354 signi cantly periodic stars were identi ed from the 3182 observed stars. Amongst them, two new possible Cephei stars were found together with a possible slowly pulsating B star (SPB), and numerous eclipsing binary systems. By using photometry of this region obtained by Forbes & Short (1996), instrumental magnitudes were transformed to a standard system in order to compare photometry results. From the constructed colour magnitude diagram of the two clusters, it could be seen that some stars, indicated by Forbes & Short (1996) to be cluster members, were in fact eld stars belonging to neither cluster. The reduction and photometry pipeline was implemented successfully on the data set, which also highlighted the importance of instrumentation and correct data analysis procedures. Possible improvements were identi ed in order to overcome di culties experienced during this study.
Thesis (MSc (Space Physics))--North-West University, Potchefstroom Campus, 2013

NASA's current plans for human spaceflight include an evolutionary series of missions based on a steady increase in capability to explore cis-lunar space, the Moon, near-Earth asteroids, and eventually Mars. Although the system architecture definition has the greatest impact on the eventual performance and cost of an exploration program, selecting an optimal architecture is a difficult task due to the lack of methods to adequately explore the architecture design space and the resource-intensive nature of architecture analysis. This research presents a modeling framework to mathematically represent and analyze the space system architecture design space using graph theory. The framework enables rapid exploration of the design space without the need to limit trade options or the need for user interaction during the exploration process. The architecture design space for three missions in a notional evolutionary exploration program, which includes staging locations, vehicle implementation, and system functionality, for each mission destination is explored. Using relative net present value of various system architecture options, the design space exploration reveals that the launch vehicle selection is the primary driver in reducing cost, and other options, such as propellant type, staging location, and aggregation strategy, provide less impact.