Individualized Models of Colour Differentiation through Situation-Specific Modelling

In digital environments, colour is used for many purposes: for example, to encode information in charts, signify missing field information on websites, and identify active windows and menus. However, many people have inherited, acquired, or situationally-induced Colour Vision Deficiency (CVD), and therefore have difficulties differentiating many colours. Recolouring tools have been developed that modify interface colours to make them more differentiable for people with CVD, but these tools rely on models of colour differentiation that do not represent the majority of people with CVD. As a result, existing recolouring tools do not help most people with CVD. To solve this problem, I developed Situation-Specific Modelling (SSM), and applied it to colour differentiation to develop the Individualized model of Colour Differentiation (ICD). SSM utilizes an in-situ calibration procedure to measure a particular user’s abilities within a particular situation, and a modelling component to extend the calibration measurements into a full representation of the user’s abilities. ICD applies in-situ calibration to measuring a user’s unique colour differentiation abilities, and contains a modelling component that is capable of representing the colour differentiation abilities of almost any individual with CVD. This dissertation presents four versions of the ICD and one application of the ICD to recolouring. First, I describe the development and evaluation of a feasibility implementation of the ICD that tests the viability of the SSM approach. Second, I present revised calibration and modelling components of the ICD that reduce the calibration time from 32 minutes to two minutes. Next, I describe the third and fourth ICD versions that improve the applicability of the ICD to recolouring tools by reducing the colour differentiation prediction time and increasing the power of each prediction. Finally, I present a new recolouring tool (ICDRecolour) that uses the ICD model to steer the recolouring process. In a comparative evaluation, ICDRecolour achieved 90% colour matching accuracy for participants – 20% better than existing recolouring tools – for a wide range of CVDs. By modelling the colour differentiation abilities of a particular user in a particular environment, the ICD enables the extension of recolouring tools to helping most people with CVD, thereby reducing the difficulties that people with CVD experience when using colour in digital environments

Anomalous trichromacy : external enhancement of colour signals, individual differences and diagnosis

Anomalous trichromacy is known to conceal a substantial range in perceptual ability, but this is not typically considered in assessments of corrective aids and diagnostic tests. In addition to the diversity caused by genetic polymorphisms, perceptual ability is thought to be influenced by little understood postreceptoral mechanisms, adding to the need for research focusing on this population. A modelling and behavioural investigation establishes the effectiveness of EnChroma filters in enhancing anomalous colour vision. Paper 1 (not yet published) employs a physiologically accurate model of colour vision to estimate the enhancements in cone-opponent signals conferred by the filters. Paper 2 (not yet published) presents behavioural validation of the model’s predictions, showing that notch filters can result in enhanced perceived saturation for deuteranomalous observers, with effects for suprathreshold perception and partial effects at absolute threshold. Paper 3 (submitted for publication) uses the physiologically accurate model of colour vision to investigate the impact of variation in edition and lighting conditions on the effectiveness of the Ishihara plates test in identifying those with mild anomalous trichromacy. The model predicts a significant impact of plate and illuminant, but no influence of edition, which is supported by the findings of a behavioural investigation. This thesis provides the first direct evidence that altering the input to the visual system using filter-based aids can impact the cone-opponent signals available to anomalous trichromats, and that this change in signal is useable by the visual system, resulting in changes to perceived saturatio

Smartdevices development for visual impairment and colour vision deficiency

The research concerns with the development of an app-based system to assist those with vision impairment to better interact with mobile phones and computers achieving maximum advantages. In particular, the system helps to detect colour deficiency and can automatically adjust view screens to increase contrast and arrive at optimal view result. Preliminary results when asking observers to evaluate the system demonstrate the advantages of the developed software system

Variability of chromatic sensitivity: fundamental studies and clinical applications

This investigation involved a number of related studies with the principal aim of assessing the variability in chromatic sensitivity in "normal" trichromats and colour deficient observers. An important outcome was the development of a new method for accurate and efficient measurement of chromatic sensitivity and the establishment of reliable statistical limits that describe the distribution of redgreen(RG) and yellow-blue (YB) chromatic sensitivity in normal trichromats. Chromatic sensitivity was assessed using a computer-based psychophysical procedure that employs spatiotemporal luminance contrast (LC) masking techniques to isolate the use of colour signals. The colour-defined stimuli were buried in dynamic LC noise and moved diagonally across a square. The subject's task is to indicate one of the four possible directions of stimulus motion by pressing the corresponding response button. The Colour Assessment and Diagnosis (CAD) test was optimised for stimulus size and background luminance level to provide an efficient measure RG and YB chromatic sensitivity. Colour detection thresholds are assessed along 16 directions in chromaticity space, selected to yield maximum information on RG and YB chromatic sensitivity loss and to distinguish between deutan and protan deficiencies. The CAD test was used to measure chromatic discrimination thresholds in 472 observers. The results made it possible to evaluate the screening and diagnostic efficiency of the CAD test in comparison with a number of established clinical colour vision tests, e.g., Nagel anomaloscope and Ishihara pseudoisochromatic plates. The specificity and sensitivity of the CAD test versus the Nagel anomaloscope (223 subjects) was found to be 100% and 97.5%, respectively. The diagnostic agreement with respect to the Nagel anomaloscope was 0.99; only two subjects showed inconsistent classification deficiency. Chromatic thresholds measured in normal trichromats were also examined and the variability amongst normal colour vision was investigated. The data obtained were used to establish the statistical limits for the standard normal observer on the CAD test. A template based on these limits was generated and provides an efficient way of separating accurately colour deficient from normal trichromats. The high specificity found is consistent with the correct detection of minimal colour deficiencies that sometimes go undetected in other colour vision tests.Molecular genetic analysis was also carried out in a small group of subjects with unusual colour deficiencies in an attempt to understand the genotype-phenotype relationship between predicted and observed colour vision losses. A comparison of genetic results from DNA sequencing and chromatic detection thresholds measured on the CAD test suggests that the separation of 30 nm between peak sensitivity of L and M normal photoreceptor pigments is not an absolute requirement for an observer to exhibit normal colour vision as assessed with conventional colour vision tests.The macular pigment (MP) optical density was also measured in 23 subjects selected for their higher than normal levels of pigment as a result of their participation in a carotenoid supplementation trial. This pre-receptoral filter absorbs light preferentially in the short wavelength region of the visible spectrum and has been shown to affect colour matches. Contrary to expectations, the findings of this investigation showed no correlation between YB thresholds and MP optical density levels. A model that explains this finding was produced confirming the observed experimental findings. In addition, the model also predicts a small improvement in RG chromatic discrimination sensitivity with increased MP optical density in the eye

Computer-Based Solutions to Support Those With Colour Vision Deficiency to Access Day-to-Day Information

In modern-day society, we are bombarded with vast amounts of electronic information which we may be expected to make decisions from. Many people have difficulties in interpreting such information due to either physical or cognitive difficulties in using electronic devices, or an inability to identify information as intended by the author. Colour Vision Deficiency (CVD) is one such problem that can cause considerable difficulty in the interpretation of diagrammatical information. This is because a Colour Vision Deficient (CVDt) person has difficulty in seeing: colour boundaries, different shades of colour and different hues. There has been some research to aid the CVDt, where the majority of the research in image processing changes or transforms colours in any given image. Such transformations use a number of different algorithms to create a CVDt friendly post-processed image from the pre-processed image. A major problem of current transformation algorithms is that they are aimed for specific contexts and cannot be used in generic contexts. For example, the transformation algorithm may be aimed at aiding the CVDt to view postprocessed images of weather maps only. The aim of this dissertation is to provide an improved post-processed image algorithm. The algorithm is intended to provide the CVDt with greater benefit by being able to interpret the information in the post-processed image correctly. The algorithm used in this dissertation is not a colour transformation algorithm instead it is a colour separation algorithm. This concept of colour separation is novel. The colour separation algorithm, which is called the Halo-Effect Algorithm (HEA), parses a given image row-by-row and pixel-by-pixel until the end of file-marker is reached and a CVDt friendly post-processed image is furnished. When there is a colour change between two identified pixels then a colour boundary has been identified within the pre-processed image and a differently coloured pixel is inserted between two, furnishing the post-processed image. As the pre-processed image is parsed row-by-row then the colour the boundary builds up to form a colour boundary interface where the different coloured pixel are inserted in the post-processed image. In this dissertation the separation pixel is always white. The build-up of inserted white pixels at the colour boundary interface of the pre-processed image produces a halo like effect in the post-processed image which is CVDt friendly. To demonstrate the efficacy of the colour separation concept, the HEA has been developed and implemented. A number of surveys have been conducted using participant responses to questions within each survey. The responses that each participant gave were then collated and analysed statistically. Two statistical techniques were used to test a number of hypotheses around the mean of a sample drawn from a normally distributed population. In this dissertation the normally distributed populations were the survey participants. From the analyses of the responses, the survey population was divided into two groups. One group was identified to have no problem with identification of pre-processed colour boundaries and were called the non-CVDt. A second group was identified to be those who had some problems with the identification of pre-processed colour boundaries and were called the indicative- CVDt. Responses from the two groups were collated and statistical analyses were then conducted to test the significance of any results obtained and also to test the validity of the algorithms under investigation. In this dissertation two currently available, but different, colour transformation algorithms were compared with the colour separation algorithm of the HEA. Each of the two transformation algorithms were originally intended for specific use. One was aimed for spectra maps and the other was aimed for background text. Statistical analyses showed that each of the transformation algorithms provided benefit to the indicative-CVDt for their specific context only. However, statistical analyses also showed that HEA fared well in each of the two specific contexts. Thus, hinting that colour separation of HEA could be used in more general contexts. To confirm that colour separation can provide greater benefit to the indicative-CVDt in more generic contexts than colour transformations further surveys were undertaken. In each survey participants were asked a number of questions about a given image where colour boundaries are expected to occur frequently. One was a map of the provinces of Australia and the other a number of differently coloured geometric shapes. Statistical analyses showed that the colour separation algorithm of HEA provided greater benefit to the indicative-CVDt than the two colour transformation algorithms in both cases. Hence, confirming that colour separation of HEA is beneficial to the indicative-CVDt in generic contexts. Colour separation of the HEA is still in its infancy and a great deal more research is required to determine how great its efficacy is. For example, clinical studies could be undertaken using two sets from one population. One set of participants who would have been diagnosed as non-CVDt, which would be identified as a control group, and a second set who would have been diagnosed as CVDt, which would be identified as a test set

Analysis of European colour vision certification requirements for air traffic control officers

The advantages of using colour in large-field, visual displays have been investigated with emphasis on ATC applications. This study examined and quantified the relationship between severity of colour vision loss in congenital deficiency and the corresponding changes in visual performance. Analysis of current colour assessment protocols and the current findings provide the basis for a new system of colour categories that can be enforced. The report also describes how a colour category can be selected for a given occupational task by examining the colour-related requirements and the applicant’s class of colour deficiency

Visual performance in the mesopic range

The aims of this work were to assess the effects of different stimulus parameters on chromatic sensitivity, with particular emphasis on the effect of retinal illumination, and to investigate aspects of suprathreshold visual performance under mesopic conditions. All investigations were performed using visual psychophysical techniques. Chromatic thresholds were obtained using dynamic luminance contrast noise to isolate responses to colour signals. The effects of stimulus size and spatial distribution were examined in normal trichromats, dichromats and subjects with acquired colour vision deficiency. The chromatic sensitivity of normal trichromats was investigated with reduction in light level. Measurements were also performed to assess the possible involvement of rods in chromatic processing at threshold. Suprathreshold performance in the mesopic range was assessed in terms of the relative contributions of colour and luminance contrast to a measure of stimulus conspicuity and to visual search time. The conspicuity of a stimulus defined by colour and luminance contrast was defined as the value of achromatic contrast of a similar stimulus with an equal perceived conspicuity. An empirical model was developed from an extensive data set of conspicuity matches, to enable prediction of conspicuity for a wide range of coloured stimuli. Visual search performance for both achromatic and coloured stimuli was investigated under mesopic conditions, and results for the coloured stimuli were compared to the measure of stimulus conspiculty combined with an achromatic search time calibration. The results revealed that chromatic sensitivity is dependent on stimulus size, spatial distribution, eccentricity of presentation and level of illumination. These factors are suggested to reflect changes in cone performance and the relative cone contributions to the postreceptoral chromatic channels. Chromatic sensitivity was found to be independent of rod activity in the mesopic range, suggesting separate processing of rod signals and threshold colour signals under mesopic conditions. Measurements of stimulus conspicuity under mesopic conditions revealed individual variations in response to both luminance contrast and chromatic signals indicative of individual differences in gain control of postreceptoral mechanisms. Conspicuity was successfully modelled as a function of photopic contrast, scotopic contrast, chromatic difference to the background and the level of illumination. The nonlinear relationship between search time and luminance contrast was found to change with reduction in light level, reflecting increased contrast thresholds and diminishing effectiveness of unit physical contrast. Mesopic visual search was also found to depend on the photopic contrast, scotopic contrast and chromatic content of the stimulus, but with an apparent greater emphasis on scotopic contrast and reduced emphasis on colour compared to the measure of stimulus conspicuity. Conspicuity was successfully used to predict visual search times, and was found to be an improved indicator of search performance than either photopic or scotopic contrast