Color-normal 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.

Poster Session: Observations and Implications of Temporary Erythropsia in a Color-Normal Observer.

Erythropsia (red vision) is characterized by the reddish or pinkish appearance of surfaces that normally appear achromatic. Erythropsia has been observed historically by people whose retinas were exposed to ultraviolet (UV) light (e.g., aphakes or pseudophakes implanted with unfiltered intraocular lenses). Erythropsia is not fully understood, but has been thought to be related to photochemical damage to short-wavelength (S) cones. Erythropsia can also occur in normal phakic eyes during intense white light adaptation. When I stare at the sunlit white siding on the southern wall of my house, after several seconds, the color changes from white to a brilliant magenta, with the central 1-2º of visual angle spared. All details in the siding fade except for the spared center. In another 10-20 seconds, the magenta turns to bluish cyan, and the previously invisible details reappear with exaggerated contrast. These observations are reminiscent of the color of S-cone increments on white adapting fields (Drum & Sternheim (2005) JOSA A: 22, 2107-19). S cones are insensitive relative to M and L cones on dim backgrounds, but they do not light-adapt like M and L cones and become relatively more sensitive at moderate adapting levels. At still higher adapting levels, S cones saturate (become unresponsive) leaving the increment a tritanopic cyan. The present observations imply that S cones initially fail to adapt to a bright white field, but then saturate, leaving the observer tritanopic.

Typical and Atypical Errors made by Color Normal and Defective Observers on Printed Pseudoisochromatic Color Vision Tests

Background: Pseudoisochromatic color vision tests are commonly used to screen for color vision deficiency (CVD). Although most color vision normal (CVN) individuals read all plates correctly, a remarkable proportion have errors. Objective: This study aimed to determine the typical and atypical error responses to the Ishihara and Waggoner PIP24 (W-PIP24) tests of CVN and CVD individuals. Methods: This study recruited 59 CVN and 63 congenital red-green CVD individuals. Participants were tested with the Ishihara and W-PIP24 tests. The participants’ responses were recorded, and typical and atypical errors were determined. Results: The rate of atypical errors in the CVN group was 21% in the Ishihara test and 9% in the W-PIP24 test, while those in the CVD group were 100% and 60%, respectively. The CVN and CVD groups tended to have more atypical errors on the Ishihara test than on the W-PIP24 test. Moreover, CVD individuals tended to have more atypical errors in the transformation plates in both tests. Conclusion: CVN individuals may misread the plates in the Ishihara and W-PIP24 tests for reasons other than the normality of color vision; therefore, counting only typical errors may eliminate the chance of CVN individuals misreading the number on the plates. The most significant finding of this study was that clinicians should perhaps only consider typical errors as “errors” on both tests.

Effect of laser eye protection devices on color perception.

Laser eye protection (LEP) devices may alter how colors are perceived in visual displays. This study investigates changes in color perception experienced by color-normal observers while wearing LEPs. Color perception with and without LEPs was measured using clinical color tests: City University Color Assessment and Diagnosis, Konan Medical ColorDx CCT-HD, and Farnsworth-Munsell 100-Hue. All LEPs induced a shift in color perception. The level of change in color perception significantly varied across LEPs. Consideration should be made when designing color displays where LEP devices are worn.

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.

Adapting to an enhanced color gamut - implications for color vision and color deficiencies.

One strategy for aiding color deficiencies is to use three narrow passbands to filter the light spectrum to increase the saturation of colors. This filtering is analogous to the narrow emission bands used in wide gamut lighting or displays. We examined how perception adapts to the greater color gamut area produced by such devices, testing color-normal observers and simulated environments. Narrowband spectra increased chromatic contrasts but also increased contrast adaptation, partially offsetting the perceived contrast enhancements. Such adaptation adjustments are important for understanding the perceptual consequences of exposure to naturally or artificially enhanced color gamut areas for both color-deficient and color-normal observers.

Potential value of color vision aids for varying degrees of color vision deficiency.

Red-green color vision deficiency (CVD) is the most common single locus genetic disorder in humans, affecting approximately 8% of males and 0.4% of females [G. H. M. Waaler, Acta Ophthalmol.5, 309 (2009)10.1111/j.1755-3768.1927.tb01016.x]; however, only about 1/4 of CVD individuals are dichromats who rely on only two cone types for color vision. The remaining 3/4 are anomalous trichromats whose CVD is milder, being based on three cone types, and who still perform remarkably well on many color-based tasks. To illustrate this, we have developed an algorithm that computes the relative loss of color discrimination in red-green CVD individuals with varying degrees of deficiency and accurately simulates their color experience for color normal observers. The resulting simulation illustrates the large gap in color discrimination between dichromats and even the most severe anomalous trichromats, showing that, relative to dichromats, the majority of anomalous trichromats can function without aids for color vision deficiency.

Physiologically Personalized Color Management for Motion Picture Workflows

<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">One of the essential mechanisms employed by the human visual system when interpreting the natural world is that of trichromatic integration of physical scene spectra by cone photoreceptors. By extension of this, different scene spectra can result in the same color sensation to an observer, a phenomenon known as metamerism. This allows imaging systems to produce realistic reproductions of scene content by the same three-channel mechanism. To predict these matches, color matching functions (CMFs) are used, which aim to describe the average spectral integration behavior of observers. However, the use of a single average observer CMF has been shown to result in impactful color rendering errors, as there exists significant variation in the spectral absorption characteristics of the eye within populations of color-normal observers. When this is crossed with the growing disparity between the spectral characteristics of emerging display technology, it becomes evident that this interobserver variability needs to be taken into account</i> .

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.

Color appearance model incorporating contrast adaptation - implications for individual differences in color vision.

Color appearance models use standard color matching functions to derive colorimetric information from spectral radiometric measurements of a visual environment, and they process that information to predict color perceptual attributes such as hue, chroma and lightness. That processing is usually done by equations with fixed numerical coefficients that were predetermined to yield optimal agreement for a given standard observer. Here we address the well-known fact that, among color-normal observers, there are significant differences of color matching functions. These cause disagreements between individuals as to whether certain colors match, an important effect that is often called observer metamerism. Yet how these individual sensitivity differences translate into differences in perceptual metrics is not fully addressed by many appearance models. It might seem that appearance could be predicted by substituting an individual's color matching functions into an otherwise-unchanged color appearance model, but this is problematic because the model's coefficients were not optimized for the new observer. Here we explore a solution guided by the idea that processes of adaptation in the visual system tend to compensate color perception for differences in cone responses and consequent color matching functions. For this purpose, we developed a simple color appearance model that uses only a few numerical coefficients, yet accurately predicts the perceptual attributes of Munsell samples under a selected standard lighting condition. We then added a feedback loop to automatically adjust the model coefficients, in response to switching between cone fundamentals simulating different observers and color matching functions. This adjustment is intended to model long term contrast adaptation in the vision system by maintaining average overall color contrast levels. Incorporating this adaptation principle into color appearance models could allow better assessments of displays and illumination systems, to help improve color appearances for most observers.

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.

Spatio-chromatic contrast sensitivity across the lifespan: interactions between age and light level in high dynamic range

We investigated spatio-chromatic contrast sensitivity in both younger and older color-normal observers. We tested how the adapting light level affected the contrast sensitivity and whether there was a differential age-related change in sensitivity. Contrast sensitivity was measured along three directions in colour space (achromatic, red-green, yellowish-violet), at background luminance levels from 0.02 to 2000 cd/m2, and different stimuli sizes using 4AFC method on a high dynamic range display. 20 observers with a mean age of 33 y. o. a. and 20 older observers with mean age of 65 participated in the study. Within each session, observers were fully adapted to the fixed background luminance. Our main findings are: (1) Contrast sensitivity increases with background luminance up to around 200 cd/m2, then either declines in case of achromatic contrast sensitivity, or remains constant in case of chromatic contrast sensitivity; (2) The sensitivity of the younger age group is higher than that for the older age group by 0.3 log units on average. Only for the achromatic contrast sensitivity, the old age group shows a relatively larger decline in sensitivity for medium to high spatial frequencies at high photopic light levels; (3) Peak frequency, peak sensitivity and cut-off frequency of contrast sensitivity functions show decreasing trends with age and the rate of this decrease is dependent on mean luminance. The data is being modeled to predict contrast sensitivity as a function of age, luminance level, spatial frequency, and stimulus size.

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.

Photoreceptor-Specific Loss of Perifoveal Temporal Contrast Sensitivity in Retinitis Pigmentosa.

PurposeInherited retinal diseases affect the L-, M-, S-cones and rods in distinct ways, which calls for new methods that enable quantification of photoreceptor-specific functions. We tested the feasibility of using the silent substitution paradigm to estimate photoreceptor-driven temporal contrast sensitivity (tCS) functions in patients with retinitis pigmentosa.MethodsThe silent substitution paradigm is based on substitution of lights of different spectral composition; this offers considerable advantage over other stimulation techniques. We used a four-primary LED stimulator to create perifoveal annular stimuli (2° inner, 12° outer diameters) and used a triple silent substitution to probe photoreceptor-selective tCS. Measurements were performed in a heterogeneous cohort of 15 patients with retinitis pigmentosa and related to those in a control group of nine color-normal healthy observers. Age differences between groups were addressed with a model of age-related normal contrast sensitivity derived from measurements in 20 healthy observers aged between 23 and 83 years.ResultsThe age-related loss of tCS amounted to 0.1 dB/year in healthy subjects across all photoreceptor subtypes. In patients, tCS was decreased for every photoreceptor subtype; however, S-cone- and rod-driven sensitivities were most strongly affected. Postreceptoral mechanisms were not affected.ConclusionsThis feasibility study provides evidence that the silent substitution technique enables the estimation of photoreceptor-selective tCS functions and can serve as an accurate biomarker of photoreceptor-specific contrast sensitivity loss in patients with retinitis pigmentosa.Translational RelevanceWe aim to develop tests of visual function for clinical trials of novel therapies for inherited retinal diseases from methods that can currently be used only in vision research labs.

Cambridge Colour Test: reproducibility in normal trichromats.

This study evaluated reproducibility of the Trivector subtest of the Cambridge Colour Test. Data for normal trichromats were obtained in Brazil ($ N = 111 $N=111) at T0, six months (T1), and 12 months later (T2), and in the United Kingdom (${ N}={79}$N=79), with the test directly followed by a retest. Coefficients of repeatability-Bland-Altman indices-for Protan, Deutan, and Tritan vectors were similar for both datasets. Intraclass correlation coefficients (ICCs)-measures of reliability-were low or moderate for these relatively homogeneous datasets; for a heterogeneous dataset, comprising color-normal and abnormal observers, ICCs were 0.80-0.98, indicating the high discriminative accuracy of the Trivector subtest.

Unique hue stimulus selection using Munsell color chips under different chroma levels and illumination conditions.

To determine the role of chroma and illumination conditions on assessments of unique hue stimuli (UHs: Y, B, R, and G) 25 color normal observers selected Munsell color chips under controlled but different light sources that included simulated D65 daylight, incandescent (A), CWF and TL84, from two rotatable trays-one containing low and the other high chroma samples. Three independent evaluations were obtained from each observer with a gap of at least 24h between assessments. A total of 2400 UH assessments were thus obtained. The mean, as well as the range and variability, in UH selections was calculated according to gender, illumination condition, and chroma. Results show statistically significant differences for uB and uR stimuli selections from the low to the high chroma sets under all lighting conditions, and for uY under light source A and CWF while differences in uG selections in different lighting conditions were statistically insignificant. No significant difference was found between male and female UH selections. Hue shift predictions based on CAT02 transform were found to agree well with observer responses under different illumination conditions. It was also found that observers' UH choices varied more for low chroma samples under different lighting conditions compared to high chroma samples. The highest variability was obtained under light source CWF, while the simulated D65 source resulted in the lowest variability in selections.

Hue rotation (HR) and hue blending (HB): Real‐time image enhancement methods for digital component video signals to support red‐green color‐defective observers

AbstractThe mutual understanding of color‐normal observers (CNOs) and color‐defective observers (CDOs) is now essential because personal color information display environments have been widely adopted. However, existing tools for CDOs offer only color discrimination; they fail to support color impression (ie, saturation and contrast). Therefore, we need a novel tool that offers help in distinguishing opponent colors, while preserving color saturation. We introduce two key techniques for realizing this difficult goal. The former is the repeated sequential display of the original and processed images to support the formation of unified correct percepts that provide discrimination of both red‐green and yellow‐blue opponent colors. One image, ie, original, exhibits correct yellow‐blue but distorted red‐green information for CDOs while the other, ie, processed, provides synthesized distinguishable red‐green but confusable yellow‐blue information for CDOs; here, hue rotation (HR) is useful for advanced users whereas hue blending (HB) is suitable for general. The latter is realized by the real‐time video processing available on smartphones; our algorithms support direct processing of the digital component video signal formats (eg, Y, CR, and CB). Subjective tests suggest that the two above‐mentioned algorithms will, along with embedding a lightweight real‐time dichromatic simulation facility for CNOs, greatly help the mutual understanding of CNOs and CDOs.

Perifoveal L- and M-cone-driven temporal contrast sensitivities at different retinal illuminances.

We established a protocol using a well-established LED stimulator to measure temporal contrast sensitivities driven by sine-wave modulation of L- and M-cones in the perifovea using triple silent substitution. The stimulus was presented in an annular field (2° inner diameter, 13° outer diameter). We validated this technique by studying the contrast sensitivity of three color normal observers at 10 different temporal frequencies (between 1 and 28 Hz) over a large range of retinal illuminances (between 0.07 and 587 phot Td), spanning the complete mesopic range. In one subject, sensitivities to counterphase modulation of L- and M-cones and in-phase modulation of L, M, and S-cones were additionally measured, which putatively reflected the parvo- and magnocellular retinogeniculate pathways, respectively. Furthermore, we performed measurements of temporal contrast sensitivities as a function of frequency at 294 phot Td in two protanopes, in two deuteranopes, and in one subject with S-cone monochromacy. Quality of isolation was satisfactory and we were able to reproduce known physiological patterns of temporal vision, such as the typical temporal contrast sensitivity functions of the L- and M-cone, the parvo- and magnocellular retinogeniculate pathways, as well as the light adaptation curves. These results will help determine optimal stimulus conditions in future studies. Results from the dichromats and the S-cone monochromat also support the quality of isolation of our protocol and underpin its potential clinical value.

Modeling, Measuring, and Compensating Color Weak Vision.

We use methods from Riemann geometry to investigate transformations between the color spaces of color-normal and color-weak observers. The two main applications are the simulation of the perception of a color weak observer for a color-normal observer, and the compensation of color images in a way that a color-weak observer has approximately the same perception as a color-normal observer. The metrics in the color spaces of interest are characterized with the help of ellipsoids defined by the just-noticeable-differences between the colors which are measured with the help of color-matching experiments. The constructed mappings are the isometries of Riemann spaces that preserve the perceived color differences for both observers. Among the two approaches to build such an isometry, we introduce normal coordinates in Riemann spaces as a tool to construct a global color-weak compensation map. Compared with the previously used methods, this method is free from approximation errors due to local linearizations, and it avoids the problem of shifting locations of the origin of the local coordinate system. We analyze the variations of the Riemann metrics for different observers obtained from new color-matching experiments and describe three variations of the basic method. The performance of the methods is evaluated with the help of semantic differential tests.