Achromatic Matching Research Articles

Chromatic adaptation for different viewing media through achromatic matches and neutrality ratings

Many corresponding color datasets have been collected under different illumination conditions over these years, providing adequate data for developing chromatic adaptation transforms (CAT). Nevertheless, these datasets exhibit notable, systematical discrepancies in visual data, probably stemming from their differences in the experiment setup and methodology. This necessitates a comprehensive examination of how the experiment-related factors influence the outcomes, accompanied by thorough discussions to establish theoretical references for the effective classification of datasets. Horizontal comparisons among these datasets indicate the influence of two crucial factors—viewing medium and experimental methods—on chromatic adaptation, albeit without systematic investigations. Additionally, the underlying mechanism contributing to the disparities observed among different media remains unclear. To address these limitations, this study selected three different media – surface colors, self-luminous colors, and independently illuminated surface colors, and two experimental methods – the achromatic matching and neutrality rating method. The results confirm the significant influence of the viewing medium on the adaptation state. Two crucial factors emerge as significant contributors: the color correlation with global illumination and the nature of the surface medium (reflective or self-luminous).

The Impact of Target Object Size and Dimensionality on the Degree of Adaptation to Global Illumination

ABSTRACT Chromatic adaptation is an important visual phenomenon that specifically influences color appearance under various illumination conditions. There were extensive studies investigating the impact of the illumination condition and the surrounding condition on chromatic adaptation. However, past studies hardly consider the properties of the stimulus object such as color, size, dimensions, etc. In this study, the impact of the size and dimensionality of the stimulus (target object) on the degree of adaptation was investigated. A series of achromatic matching experiments were conducted in a lighting booth, with the adapting field varying in chromaticity and the object varying in size and dimensionality, to collect corresponding color data. Results indicate that the properties of the stimulus, such as the dimensionality and size, can significantly influence the adaptation state, independent of illumination chromaticity. But to apply the results in the real application may be restricted to the specific setup (used in this study) with a separately illuminated stimulus, which needs further investigation.

Effect of surrounding objects in the adapting scene on chromatic adaptation.

Most of the existing chromatic adaptation transforms (CATs) were developed for flat uniform stimuli presented in a uniform background, which substantially simplifies the complexity of the real scene by excluding surrounding objects from the viewing field. The impact of the background complexity, in terms of the spatial properties of the objects surrounding the stimulus, on chromatic adaptation is ignored in most CATs. This study systematically investigated how the background complexity and color distribution affect the adaptation state. Achromatic matching experiments were conducted in an immersive lighting booth, with the illumination varying in chromaticity and the adapting scene varying in surrounding objects. Results show that compared to the uniform adapting field, increasing the scene complexity can significantly improve the degree of adaptation for the Planckian illuminations with low CCT levels. In addition, the achromatic matching points are substantially biased by the color of the surrounding object, implying the interactive effect of the illumination color and the dominant scene color on the adapting white point.

Transition type influences the adaptation state under dichromatic illuminations.

The CATs models proposed over these years (such as CMCCAT97, CAT02 and CAT16) were derived from simple stimuli surrounded by a uniform background with a single illuminant. However, the real scene always consists of more than one illumination, especially in many artificially lit environments. Some previous studies indicate an influence of the transition type between two illuminations on the adaptation state, but the visual data is insufficient to conclude a general trend applicable for any color pair. To systematically investigate how the transition type and illumination color pair interactively influence the adapted white point and degree of adaptation, a series of achromatic matching experiments were conducted under (simultaneously) spatially dichromatic illuminations. Transition type was found to have an impact on the adaptation state, but it is significant only for an illumination pair with a large color difference. In addition, for those sharp-transitioned dichromatic illuminations, the illumination that more easily gets adapted tends to have a higher contribution to the adapted white point than the other one. A more comprehensive CAT model for dichromatic illuminations was derived from the collected visual data.

Impact of matching field size on color matching (functions) accuracy

AbstractAccurate colorimetry starts with accurate color matching functions (CMFs). Due to changes in the macular pigment and cone pigment optical densities at different retinal locations, different CMFs are required for different stimulus field sizes. To characterize the accuracy of the CIE recommendation for the use of 2° and 10° standard CMFs and the field‐size dependent CIEPO06 model, in this study, a series of achromatic matching experiments were performed with 2°, 4°, 6°, 8°, and 10° bipartite fields using spectrally narrowband primaries. Using the CIEPO06 model, optimal field sizes were estimated that minimize the chromaticity differences between the spectrally narrowband observer matches and the spectrally broadband achromatic target. It was found that the optimal field size estimated using the CIEPO06 model is close to half the actual bipartite field size in most cases, except for the 2° field. The discrepancy between the 10° bipartite field in Stiles & Burch's experiments and our optimal field size (6.54°) was assumed to be due to different individual color comparison strategies. However, the results of experiments requiring specific observer gaze positions did not support this assumption and the reason for the discrepancy remains unclear. Confirming our earlier results, the primary set (636, 521, 447 nm) was again found to be largely insensitive to changes in CMFs and to provide the most accurate matches under various fields of view. The inter‐ and intra‐observer variability ellipses for 2° matches are larger than those for 10°, consistent with Brown's finding for color discrimination ellipses. The magnitude of the intraobserver variability was similar for all field sizes, except for 2° field size, where matching errors were larger for some primary sets.

Predictive performance of the standard and the modified von Kries chromatic adaptation transforms.

To investigate chromatic adaptation and develop chromatic adaptation transforms (CATs), many psychophysical experiments have been conducted to collect corresponding colors (CC) under various illumination conditions. Most modern CATs have been developed based on a database of CC sets collected in the 20th century. More recently, several additional CC sets have been collected by Smet et al., Wei et al., and Ma et al. using memory color matching or achromatic matching methods. The analysis of these CC data indicates that for yellowish (located on or close to the Planckian locus) and greenish illuminations, the short-wave (S) sensitive cones show a lower degree of adaptation compared to the long-wave (L) and medium-wave (M) sensitive cones. This can result in a large prediction error of the standard von Kries CAT, which adopts a single degree of adaptation value for all three cone types. A modified von Kries CAT is proposed that accounts for these differences between the L-, M- and S-cone signals by applying a compression to the rescaling factor for the S-cones. It outperforms the standard von Kries CAT for the Breneman-C, Smet, Wei, and Ma data, while for other data sources the two CATs have similar performance.

Egg Discrimination in an Open Nesting Passerine Under Dim Light Conditions

Many hosts of avian brood parasites such as the common cuckoo (Cuculus canorus) show refined egg discrimination behaviour. Egg recognition in most open-nesting hosts seems to be based entirely on differences in colour. However, hole- and dome-nesting hosts may rely largely on luminance contrasts. Here, we studied egg rejection behaviour in nightingales (Luscinia megarhynchos), an open-nesting species that nests in deeply shadowed positions and lays very specific dark olive-green eggs. Although being theoretically suitable as hosts of the cuckoo, nightingales are very rarely parasitized and no cuckoo egg morph mimicking nightingale eggs is known. Thus, we predicted high rejection rate of foreign eggs, but because of the dim nesting environments, luminance contrasts would be an important cue in egg rejection decisions, similar to cavity- or dome-nesting species. We experimentally parasitized nightingale nests with two groups of model egg types: ‘bright eggs’ and ‘dark eggs’. Within each group, one of the egg types was an effective match while the other type was a poor colour match (whitish vs. pale blue and olive-green vs. black).We used a discrimination visual model to quantify host-model egg similarity and compared egg rejection predicted by the model with the observed rejection pattern. Consistent with a scenario of largely luminance-based egg recognition, blue and white eggs, which had larger achromatic mismatching, were rejected at a higher relative rate than the better achromatic matching black and green eggs. Nightingales showed strong aggression to a cuckoo dummy, suggesting that they were involved in coevolutionary interactions with the cuckoo in the past. However, because of the highly distinct appearance of nightingale eggs relative to the other sympatrically breeding passerines, and the largely luminance-based egg recognition, this arms race was likely terminated at an early stage.

Egg colour mimicry in the common cuckooCuculus canorusas revealed by modelling host retinal function

Some parasite cuckoo species lay eggs that, to the human eye, appear to mimic the appearance of the eggs of their favourite hosts, which hinders discrimination and removal of their eggs by host species. Hitherto, perception of cuckoo-host egg mimicry has been estimated based on human vision or spectrophotometry, which does not account for what the receivers' eye (i.e. hosts) actually discriminates. Using a discrimination model approach that reproduces host retinal functioning, and museum egg collections collected in the south of Finland, where at least six different races of the European cuckoo (Cuculus canorus) coexist, I first assess whether the colour design of cuckoo eggs of different races maximizes matching for two favourite avian hosts, viz. the redstart (Phoenicurus phoenicurus) and the pied wagtail (Motacilla alba). Second, I assess the role of nest luminosity on host perception of mimicry by the same two hosts. Phoenicurus-cuckoo eggs showed a better chromatic matching with the redstart-host eggs than other cuckoo races, and in most cases can not be discriminated. Sylvia-cuckoo eggs, however, showed better achromatic matching with redstart-host eggs than Phoenicurus-cuckoo eggs. Also, Motacilla-cuckoo eggs showed poorer chromatic and achromatic matching with pied wagtail-host eggs than Sylvia-cuckoo eggs. Nest luminosity affected chromatic and achromatic differences between cuckoo and host eggs, although only minimally affected the proportion of cuckoo eggs discriminated by chromatic signals. These results reveal that cuckoo races as assessed by humans do not entirely match with host perception of matching and that achromatic mechanisms could play a main role in the discrimination of cuckoo eggs at low-light levels.

Time course of chromatic adaptation for color appearance and discrimination

Adaptation to a steady background has a profound effect on both color appearance and discrimination. We determined the temporal characteristics of chromatic adaptation for appearance and discrimination along different color directions. Subjects were adapted to a large uniform background made up of a CRT screen and a 45×64° wall, illuminated by computer controlled lamps. After an instant change in background color along a red–green or blue–yellow color axis, we measured thresholds for the detection of increments along the same axes at fixed times between 25 ms and 121 s. Analogously, color appearance was determined using achromatic matching. Three components of adaptation could be identified by their temporal characteristics. A slow exponential time course of adaptation with a half-life of about 20 s was common to appearance and discrimination. A faster component with a half-life of 40–70 ms — probably due to photoreceptor adaptation — was also common to both. Exclusive for color appearance, there was a third, extremely rapid mechanism with a half-life faster than 10 ms. This instantaneous process explained more than 50% of total adaptation for color appearance and could be shown to act in a multiplicative manner. We conclude that this instantaneous adaptation mechanism for color appearance is situated at a later processing stage, after mechanisms common to appearance and discrimination, and is based on multiplicative spatial interactions rather than on local, temporal adaptational processes. Color appearance, and thus color constancy, seems to be determined in large part by cortical computations.

The color constancy of the red-green color blind

The color constancy of 5 normal and 10 red-green color deficient (4 protanopes, 3 deuteranopes, 3 deuteranomalous trichromats) observers was investigated by an achromatic matching task, in which they were required to adjust the color of a central patch within a scene until it appeared as a neutral gray. The patch was presented in the middle of a CRT Mondrian display, which was initially set to CIE Illuminant C or D65 and then shifted along either the red-green cardinal axis, blue-yellow cardinal axis, or Planckian locus. Despite their significantly higher red-green discrimination thresholds, color deficient observers display color constancy similar to that of normal observers along all three axes. However, their variability is greater for settings along the red-green cardinal axis. © 2000 John Wiley & Sons, Inc. Col Res Appl, 26, S209–S213, 2001