Color-deficient Observers Research Articles

A dual-parameter evaluation method for color-enhancement technologies and its application to lighting-spectrum optimization for color-deficient observers

Over 200 million people worldwide suffer from color vision deficiency (CVD), leading to a compromised perception of the color world. Despite the availability of various color enhancement technologies (CETs), assessing their actual performance has remained challenging due to the lack of a comprehensive evaluation method. In this paper, we propose a dual-parameter metric system that quantitatively evaluates CETs' capacity to improve CDOs' color discrimination ability and color fidelity relative to color-normal observers (CNOs). We validated this method by comparing its evaluation results with those of prior studies that relied on psychophysical experiments. Our proposed dual-parameter evaluation system can also be employed to optimize CET-based solutions. As a preliminary exploration, we optimized lighting spectra using LED color mixing for CVD-friendly illumination applications, which demonstrated a clear improvement in color vision for color-deficient observers while maintaining good color fidelity for CNOs’ color vision.

Poster Session II: XR-based personalized active aid for color deficient observers.

In a previous study, Xu et al. (Optics Express, 2022) investigated the efficacy of active aid in the form of personalized image enhancement to increase color discrimination ability in color-deficient observers (CDO). The study parameterized severity of color deficiency, the wavelength shift of cone spectral fundamentals, and the spectral distribution of display primaries. The first parameter was derived by computing the confusion index of the CDO, employing a modified version of the FM-100 test (ZJU50Hue). The second parameter was determined via evaluation of a wavelength-shifted ZJU50Hue test on color-normal observers (CNO). The three parameters were used to model the gamut mapping between CNO and CDO. In this study, extended reality (XR) based modules were developed to acquire these parameters and consequently tailor the headset display to assist CDOs. We chose to implement the Cambridge color test over the ZJU50Hue test as threshold results along the protan, deutan, and tritan lines are more informative than a single confusion index. Preliminary results on a calibrated Varjo XR-3 headset suggest a high correlation between the standard CCT and our XR-based trivector test. As the calibration, simulation and modeling processes all take place in the same HMD, we intend to model the CNO-CDO gamut mapping into a post-process graphics shader to enhance the camera input of the XR-3 and perform a paper-based Ishihara test for evaluation of real-world color discrimination efficacy.

Daltonization or colour enhancement: potential uses and limitations [Invited

The main perceptual-cognitive limitations of CDOs (Colour Deficient Observers) are analysed, along with the uses and limitations of tools that either transform images so that CNOs (Colour Normal Observers) see them as CDOs (simulation) or transform images so that CDOs can use them as CNOs (daltonization). The four main uses of colour (comparative, denotative, connotative, and aesthetic) are analysed, along with their relation to, alternatively, the ability to discriminate colour stimuli or to categorize colours. These uses of colour are applied to analyse the possible effects of daltonization tools.

Personalized image enhancement method for color deficient observers.

A personalized image enhancement method is proposed to improve color vision in hereditary color vision deficiency (CVD). It is divided into two stages: evaluation of CVD and gamut mapping for image enhancement. These two separate stages are connected via a psychophysical experiment, through which the deficiency test result expressed using the C-index can be further transformed into a physical parameter, namely the wavelength shift of the cone fundamental. Experiments conducted by the color-deficient observers (CDOs) validated this proposed method, and it is emphasized that the proposed method is just serving as a template for image enhancement. A more advanced simulation model, a more accurate assessment method, or a more sophisticated gamut mapping algorithm can yield a better result.

Initial findings on changing the background in pseudo-isochromatic charts

Color vision deficiency is a common affliction for males, impacting about 8% of the population. The effects of this – colloquial – color blindness is the inability or limited ability to distinguish colors. A typical problem might be that a color changing LED, changing between red and green to indicate two states, will not be differentiated. There are multiple ways to detect and distinguish color deficient people, ranging from genetic testing, to simple pseudo-isochromatic charts, as exemplified by the likely most known Ishihara charts, to elaborate color matching and color sorting tests, as exemplified by the Farnsworth-Munsell 100 Hue test. In this talk describe initial experimental data on changing the background color – or the color “in between the dots” - for a pseudo-isochromatic chart color deficiency test. For the experiment, we replaced the white background with 4 different neutral gray-level values and measured the performance of known color deficient observers on these charts as a function of the new background. Though preliminary, the data show a significant difference in the performance of color deficient observers, despite the main pseudo-isochromatic colors staying the same.

Gamut mapping based image enhancement algorithm for color deficiencies.

This study presents an approach for enhancing color images for color vision deficiencies. The proposed approach is separated into three stages. First, the type and severity of a color deficient observer (CDO) were evaluated. Following that, the perceived color gamut was assessed using a physiologically-based color deficiency simulation model. Finally, images prepared for color normal observers (CNOs) were re-colored using a gamut mapping method to map colors from the gamut of a CNO to that of a CDO. Two psychophysical experiments were carried out to validate this method, and the results suggest that it is a promising solution for the CDOs. The unique feature of the present method is to include a gamut mapping method to enhance the color discrimination by preserving the perceived hue.

Examining Spatial Attributes for Color Deficient Observers

Color deficiency is a common affliction for males, with about 8% of the male population suffering from some form of – colloquial – color blindness. In common description, this is interpreted as the inability to perceive certain colors from a sensory standpoint. If that description is sufficiently complete, spatial attributes of the color signal should not influence the visual experience of a Color Deficient Observer (CDO).In this paper we describe the set-up and results of an experiment that is intended to vary the spatial attributes of a color deficiency test when shown to an observer. For this, we modified color vision charts to maintain their colorimetric attributes while varying spatial attributes and we measured color deficient observers with respect to their response accuracy and their response speed. We show results that indicate that there is a clear influence of color proximity in the responses.

Analysis of Hue Circle Perception of Congenital Red-green Congenital Color Deficiencies Based on Color Vision Model

To investigate individual property of internal color representation of congenital red-green color-deficient observers (CDOs) and color-normal observers (CNOs) precisely, difference scaling experiment using pairs of primary colors was carried out for protans, deutans, and normal trichromats, and the results were analyzed using multi-dimensional Scaling (MDS). MDS configuration of CNOs showed circular shape similar to hue circle, whereas that of CNO showed large individual differences from circular to U- shape. Distortion index, DI, is proposed to express the shape variation of MDS configuration. All color chips were plotted in the color vision space, (L, r/g, y/b), and the MDS using a non-linear conversion from the distance in the color vision space to perceptual difference scaling was successful to obtain U-shape configuration that reflects internal color representation of CDOs.

Color image evaluation of congenital red-green color deficient and normal color vision observers

How and to what extent the increase of Cab * affects on various subjective evaluations for congenital red-green color deficiency (CVD) and normal color vision (NCV) observers was investigated using scenery, food, and graph images. Results of "Pale vs Deep" evaluation indicate similar tendency for all color vision types in all test images, indicating that CVDs recognize the saturation change of images similar to NCVs using some kind of strategy. Individual differences of the CVDs in the results of other adjective pairs such as "Unnatural vs Natural" are generally larger than those of NCVs. Some color combinations in the graph images are indiscriminable for either protan or deutan, and thus are not recommended to be used.

Adaptive Changes in Color Vision from Long-Term Filter Usage in Anomalous but Not Normal Trichromacy

For over 150 years, spectrally selective filters have been proposed to improve the vision of observers with color vision deficiencies [1]. About 6% of males and <1% of females have anomalies in their gene arrays coded on the X chromosome that result in significantly decreased spectral separation between their middle- (M-) and long- (L-) wave sensitive cone photoreceptors [2]. These shifts alter individuals' color-matching and chromatic discrimination such that they are classified as anomalous trichromats [3, 4]. Broad-band spectrally selective filters proposed to improve the vision of color-deficient observers principally modify the illuminant and are largely ineffective in enhancing discrimination or perception because they do not sufficiently change the relative activity of M- and L-photoreceptors [5, 6]. Properly tailored notch filters, by contrast, might increase the difference of anomalous M- and L-cone signals. Here, we evaluated the effects of long-term usage of a commercial filter designed for this purpose on luminance and chromatic contrast response, estimated with a signal detection-based scaling method. We found that sustained use over two weeks was accompanied by increased chromatic contrast response in anomalous trichromats. Importantly, these improvements were observed when tested without the filters, thereby demonstrating an adaptive visual response. Normal observers and a placebo control showed no such changes in contrast response. These findings demonstrate a boosted chromatic response from exposure to enhanced chromatic contrasts in observers with reduced spectral discrimination. They invite the suggestion that modifications of photoreceptor signals activate a plastic post-receptoral substrate that could potentially be exploited for visual rehabilitation.

Computerized simulation of color appearance for anomalous trichromats using the multispectral image

Most color simulators for color deficiencies are based on the tristimulus values and are intended to simulate the appearance of an image for dichromats. Statistics show that there are more anomalous trichromats than dichromats. Furthermore, the spectral sensitivities of anomalous cones are different from those of normal cones. Clinically, the types of color defects are characterized through Rayleigh color matching, where the observer matches a spectral yellow to a mixture of spectral red and green. The midpoints of the red/green ratios deviate from a normal trichromat. This means that any simulation based on the tristimulus values defined by a normal trichromat cannot predict the color appearance of anomalous Rayleigh matches. We propose a computerized simulation of the color appearance for anomalous trichromats using multispectral images. First, we assume that anomalous trichromats possess a protanomalous (green shifted) or deuteranomalous (red shifted) pigment instead of a normal (L or M) one. Second, we assume that the luminance will be given by L+M, and red/green and yellow/blue opponent color stimulus values are defined through L-M and (L+M)-S, respectively. Third, equal-energy white will look white for all observers. The spectral sensitivities of the luminance and the two opponent color channels are multiplied by the spectral radiance of each pixel of a multispectral image to give the luminance and opponent color stimulus values of the entire image. In the next stage of color reproduction for normal observers, the luminance and two opponent color channels are transformed into XYZ tristimulus values and then transformed into sRGB to reproduce a final image for anomalous trichromats. The proposed simulation can be used to predict the Rayleigh color matches for anomalous trichromats. We also conducted experiments to evaluate the appearance of simulated images by color deficient observers and verified the reliability of the simulation.

Multiscale Daltonization in the Gradient Domain

Abstract We propose a daltonization method that enhances chromatic edges and contrast for color-deficient people by optimizing the gradient of an image. We rotate and scale the error gradient between the original and its simulation in the color space into the direction of optimal visibility that is orthogonal to both the main direction of information loss and the direction of lightness. Then, we reintegrate the daltonized image version from the modified gradient through an iterative diffusion process. Moreover, we include multiscaling to guarantee optimal daltonization on different scales of the image. Also, we provide an interface for data attachment modules designed to maintain naturalness of memory colors like neutral colors. We evaluate and compare our proposed method to other top-performing daltonization methods in behavioral and psychometric experiments. A visual-search experiment assessing performance of the attentional mechanism of the human visual system before and after daltonization measures the greatest improvement in accuracy for our proposed method compared to the original and all investigated daltonization methods. It also reveals optimal results for both natural and Ishihara images among both protan and deutan color-deficient observers. Furthermore, we can deduce from the results of a pairwise preference evaluation that our proposed method is preferred highest amongst all color-deficient people in total. Our proposed method is also ranked among the most preferred daltonization methods for both protan and deutan color-deficient observers individually.

Contributions of luminance and S-cone signals to color discrimination and supra-threshold color difference in color-deficient observers

Contributions of luminance and S-cone signals to color discrimination and supra-threshold color difference in color-deficient observers

On the edge: A scalable daltonization method focusing chromatic edges and contrast

Color Vision Deficiency (CVD) leads to a reduced capability to identify chromatic edges and contrast and may cause significant problems in various color tasks like, for example, comparative color tasks. Many daltonization methods to improve color perception of color-deficient people, however, change naturalness of confusion colors, which might complicate other color tasks like, for example, connotative and denotative color tasks. Thus, we present a daltonization method focusing on the enhancement of chromatic edges and contrast while preserving the naturalness of object colors as good as possible. Our proposed method, Yoshi-II-edge, is based on a previously presented method, Yoshi-II, which projects and rotates the lost information by color-deficient observers along the direction of optimal visibility. Yoshi-II-edge limits this enhancement to chromatic edges and contrast by computing an edge map obtained from the gradient of the error image between the original and its simulation. Furthermore, we propose a threshold and dilation to influence the width of the daltonized edge. We show that the performance of this method depends on the juxtaposition of confusion colors in the image. More precisely, Yoshi-II-edge performs well in images with adjacent areas of confusion colors but performs poorly in images with non-adjacent areas of confusion colors.

Color constancy of color-deficient observers under illuminations defined by individual color discrimination ellipsoids.

We explored the color constancy mechanisms of color-deficient observers under red, green, blue, and yellow illuminations. The red and green illuminations were defined individually by the longer axis of the color discrimination ellipsoid measured by the Cambridge Colour Test. Four dichromats (3 protanopes and 1 deuteranope), two anomalous trichromats (2 deuteranomalous observers), and five color-normal observers were asked to complete the color constancy task by making a simultaneous paper match under asymmetrical illuminations in haploscopic view on a monitor. The von Kries adaptation model was applied to estimate the cone responses. The model fits showed that for all color-deficient observers under all illuminations, the adjustment of the S-cone response or blue-yellow chromatically opponent responses modeled with the simple assumption of cone deletion in a certain type (S-M, S-L or S-(L+M)) was consistent with the principle of the von Kries model. The degree of adaptation was similar to that of color-normal observers. The results indicate that the color constancy of color-deficient observers is mediated by the simplified blue-yellow color system with a von Kries-type adaptation effect, even in the case of brightness match, as well as by a possible cone-level adaptation to the S-cone when the illumination produces a strong S-cone stimulation, such as blue illumination.

Quality of color coding in maps for color deficient observers

For a color deficient observer, the quality of a map or other information design may be defined as the ability to extract features. As color is such important conveyor of information, the colors need to appear correct and be perceived in the desired and intended way. As color appearance is affected by the size of the stimuli, the task of discriminate colors may be even more difficult for a color vision deficient observer. In order to investigate the discriminability of the color coding in an official Norwegian map product, we conducted an experiment involving both color deficient and color normal observers. Also, we investigate to what extent the ability to discriminate colors is influenced by size of the visual field. The experiment revealed that the color vision deficient observers made significant more errors than the normal observers, especially when the visual angle was reduced.

Saliency-based color accessibility.

Perception of color varies markedly between individuals because of differential expression of photopigments in retinal cones. However, it has been difficult to quantify the individual cognitive variation in colored scene and to predict its complex impacts on the behaviors. We developed a method for quantifying and visualizing information loss and gain resulting from individual differences in spectral sensitivity based on visual salience. We first modeled the visual salience for color-deficient observers, and found that the predicted losses and gains in local image salience derived from normal and color-blind models were correlated with the subjective judgment of image saliency in psychophysical experiments, i.e., saliency loss predicted reduced image preference in color-deficient observers. Moreover,saliency-guided image manipulations sufficiently compensated for individual differences in saliency. This visual saliency approach allows for quantification of information extracted from complex visual scenes and can be used as an image compensation to enhance visual accessibility by color-deficient individuals.

A Content-Dependent Naturalness-Preserving Daltonization Method for Dichromatic and Anomalous Trichromatic Color Vision Deficiencies

Color vision deficiency represents an inability to perceive differences between certain colors that can be distinguished in the case of regular color vision. This article proposes a new daltonization method for re-coloring image segments perceived as confusingly colored by color deficient observers and, thus, to improve their perceived image quality. The idea behind this approach is that only one image color center should be located on one confusion line. If colors of two or more segments lie on the same confusion line, then they should be remapped in a direction perpendicular to the confusion line taking into account the image content&#x2014;the color distribution of other segments. The method conserves the image naturalness by restricting, for each segment center, an area of admissible remapping. This achieves re-coloring balance where colors are made sufficiently distinguishable from each other, but they do not deviate too much from the original image colors. The proposed re-coloring concept is applicable to all types of dichromacy and anomalous trichromacy with adjustment for their set of confusion lines. The simulation results show that the re-coloring converts an original image to a version with improved color distinction, confirmed by evaluations of eight color deficient users. An intentionally chosen example demonstrates when and why the proposed method performs better against content-independent methods. Furthermore, results and subjective evaluations indicate that the method provides more natural re-coloring results for anomalous trichromats than in the case of content-dependent methods optimized for dichromats.

Categorical color perception of color normal and deficient observers

Color changes as a continuous variable. We can discriminate millions of colors, but at the same time we categorize colors into discrete color names. Dichromat (color deficient) observers also categorize colors in manners very similar to that of color normal (trichromat) observers despite the fact that color deficient observers confuse many colors. In this study, we investigated characteristics of categorical color perception of trichromat and dichromat under various chromatic illuminations. Observers named 424 OSA uniform color samples using only the Berlin and Kay’s eleven basic color terms. Categorical color perception of normal trichromat was found to be robuster under strong chromatic illuminants than dichromats. Dichromats could utilize a lightness cue to name indistinguishable colors. It is unlikely that dichromats have the same categorical color mechanism as normal trichromat has. The present results support that there is the physiological substrate for categorical color perception specific to trichromat or dichromats.

Correction: Recognition Memory for Colored and Black-and-White Scenes in Normal and Color Deficient Observers (Dichromats)

Correction: Recognition Memory for Colored and Black-and-White Scenes in Normal and Color Deficient Observers (Dichromats)