溝上 陽子

The recognition of spatial structures is important for color constancy because we cannot identify an object's color under different illuminations without knowing which space it is in and how that space is illuminated. To show the importance of the natural structure of environments on color constancy, we investigated the way in which color appearance was affected by unnatural viewing conditions in which a spatial structure was distorted. Observers judged the color of a test patch placed in the center of a small room illuminated by white or reddish lights, as well as two rooms illuminated by white and reddish light, respectively. In the natural viewing condition, an observer saw the room(s) through a viewing window, whereas in an unnatural viewing condition, the scene structure was scrambled by a kaleidoscope-type viewing box. Results of single room condition with one illuminant color showed little difference in color constancy between the two viewing conditions. However, it decreased in the two-rooms condition with a more complex arrangement of space and illumination. The patch's appearance under the unnatural viewing condition was more influenced by simultaneous contrast than its appearance under the natural viewing condition. It also appears that color appearance under white illumination is more stable compared to that under reddish illumination. These findings suggest that natural spatial structure plays an important role for color constancy in a complex environment. (c) 2014 Optical Society of America

色覚異常者は,色弁別が困難である色にもかかわらず,多様な色名を用いている.これは,色覚異常者が周囲の色を手がかりにして,色名を決定しているためと考えられる.本稿では,その色認識のメカニズムを明らかにするため,観察条件と色の手がかりの条件によって,また,色覚異常の強度によって,どのようにカテゴリカル色知覚が変化するのかを調べた.応答方法は,Free Sorting Task (FST)とCategorical Color Naming Method (CCNM)の2種類で行った.また,色票を1枚ずつ評価する方法と全色票を見比べて評価する方法を比較した.さらに,色見本を使用し,色の手がかりによってカテゴリカル色知覚が変化するのかを調べた.その結果,弱度の2型3色覚者は色覚正常者とほぼ似た応答をし,強度の2型3色覚者は異なる応答をした.これより,色覚異常者と色覚正常者とのカテゴリカル色知覚における色名応答の差は,色弁別で定義されている色覚異常の強度に依存することが示唆された.さらに,強度の2型3色覚者は,色の手がかりや複数の呈示によってカテゴリカル色知覚がより安定し,より色覚正常者に近くなることが分かった.

周囲環境の影響を受けて色知覚が変わる現象は,同時明度・色対比効果や色域拡大効果等が知られており,それらの研究の多くは平面の刺激について調べられている.空間においても,周囲環境の明度構成により空間の明るさ感が変化すると物体の明度知覚が影響を受けると報告されている.しかし,周囲の明度構成が彩度知覚に与える影響,また,平面と空間による違いについては明らかではない.本論文では,空間での周囲環境の明度が物体の明度と彩度の知覚に与える影響を明らかにするため,無彩色で構成されたミニチュアの室内模型内での色パッチの見えを,マンセルカラーチャートとのマッチングにより求めた.室内の明度構成が低・中・高の単一明度に加え,複数明度の混合条件,最高明度を変化させた条件,さらに平面を用いた条件を比較した.その結果,室内模型内を低明度で構成したときの色パッチの見えは,バリュー,クロマともに高くなった.同様に平面上での色パッチの見えを調べたところ,空間に比べて周囲明度の違いによる色パッチの彩度知覚変化は小さかった.これらの結果は,空間での周囲環境の明度構成の違いがその空間の明るさ感を変化させ,それに基づいてパッチの明度知覚が決定されたものと考えられる.さらにその際,明度知覚が変化しても見えのxy色度は保持されたため,結果として彩度知覚が変化したことを示唆している.

We carried out the color matching experiments to investigate whether a colorimetric match between light sources of different spectral power distributions gives the same color appearance. A high intensity discharge (HID) light or a white LED light with similar chromaticity coordinates was used for a reference stimulus. The matching stimulus was made by a mixture of red-, green- and blue-LED primary with narrow bandwidth. It was found that the CIE 1931 color matching functions could not predict a color match between the HID light source and the white LED. The HID light source was perceived more bluish than the white LED. We examined various color matching functions whether they predict color matches among light sources of different spectral power distribution. We tested existing color matching functions including the CIE 1931, the CIE 1964, the Stiles and Burch 2 degrees, the Stiles and Burch 10 degrees, and the Judd's revised color matching functions. Among these color matching functions, the Judd's revised color matching functions performed the best prediction for the experimental results.

This study provides some methods in order to enhance the six-primary color space. It contains three stages: (1) sRGB expansion, (2) specialized gamut mapping (3) through a psychophysical experiment to Inspect the result. According to the result, the proposed method is better than the non-corrected one.

Although the color measurement of facial skin becomes more common in dermatology and cosmetics, little is known about the relationship between subjective color perception and colorimetric values in facial skin. In this study, the possible relationships among perceived whiteness and the metric lightness, chroma and hue angle of Japanese females' facial skin color were investigated. First, the perceived brightness of the facial skin of Japanese females was evaluated visually and compared with metric lightness, chroma and hue angle, and the effect of hue and chroma on the perceived brightness was discussed. Second, a psychophysical experiment on the whiteness of the facial images and synthesized skin color plate images was conducted for examining the effect of hue and chroma on the perceived whiteness more precisely and independently. The results of two experiments showed that in regard to the facial skin color of the Japanese female, metric lightness disagrees with perceived whiteness or brightness in a narrow lightness range. The reddish facial skin color appeared brighter or whiter than that of a yellowish one in high lightness regions, and the low-chroma facial skin color appeared brighter or whiter than a high-chroma one. However, in the color plate images, a change in perceived whiteness by hue could not be confirmed, and the change in perceived whiteness by chroma was weaker than that from facial images. These results indicated that a higher-level process of face recognition affected whiteness perception, and the criterion of facial skin whiteness was determined by facial skin color distribution. (c) 2011 Wiley Periodicals, Inc. Col Res Appl, 2011;

Natural illuminant and reflectance spectra can be roughly approximated by a linear model with as few as three basis functions, and this has suggested that the visual system might construct a linear representation of the spectra by estimating the weights of these functions. However, such models do not accommodate nonlinearities in color appearance, such as the Abney effect. Previously, we found that these nonlinearities are qualitatively consistent with a perceptual inference that stimulus spectra are instead roughly Gaussian, with the hue tied to the inferred centroid of the spectrum [J. Vision 6(9), 12 (2006)]. Here, we examined to what extent a Gaussian inference provides a sufficient approximation of natural color signals. Reflectance and illuminant spectra from a wide set of databases were analyzed to test how well the curves could be fit by either a simple Gaussian with three parameters (amplitude, peak wavelength, and standard deviation) versus the first three principal component analysis components of standard linear models. The resulting Gaussian fits were comparable to linear models with the same degrees of freedom, suggesting that the Gaussian model could provide a plausible perceptual assumption about stimulus spectra for a trichromatic visual system. (c) 2011 Optical Society of America

We examined whether the perception of the colorfulness of an image is influenced by the adaptation of the visual system to natural and shuffled images with different degrees of saturation. In the experiment, observers first became adapted to several images with different levels of saturation and then their colorfulness perception of a test image was measured. The results show that their perception of colorfulness was influenced by their adaptation to the saturation of images. The effect was stronger following adaptation to natural images than to images consisting of a shuffled collage of randomized color blocks, which suggests that the naturalness of the spatial structure of an image affects the strength of the effect. (c) 2012 Optical Society of America

Results from psychophysics and single-unit recordings suggest that color vision comprises multiple stages of processing. Postreceptoral channels appear to consist of both a stage of broadly tuned opponent channels that compare cone signals and a subsequent stage, which includes cells tuned to many different directions in color space. The chromatic visual evoked potential (crVEP) has demonstrated chromatic processing selective for cardinal axes of color space. However, crVEP evidence for higher-order color mechanisms is lacking. The present study aimed to assess the contribution of lower- and higher-order color mechanisms to the crVEP by using chromatic contrast adaptation. The results reveal the presence of mechanisms tuned to intermediate directions in color space in addition to those tuned to the fundamental cardinal axes. (c) 2012 Optical Society of America

The Abney effect refers to changes in the hue of lights as they are desaturated. Normally the purity is varied by desaturating with a fixed spectrum. Mizokami et al. [J. Vis. 6, 996 (2006)] instead varied purity by using Gaussian spectra and increasing their bandwidth. Under these conditions the hues of lights at short and medium wavelengths tended to remain constant and thus were tied to a fixed property of the stimulus such as the spectral peak, possibly reflecting a compensation for the spectral filtering effects of the eye. Here we test this account more completely by comparing constant hue loci across a wide range of wavelengths and between the fovea and periphery. Purity was varied by adding either a fixed spectrum or by varying the spectral bandwidth, using an Agile Light Source capable of generating arbitrary spectra. For both types of spectra, hue loci were approximated by the Gaussian model at short and medium wavelengths, though the model failed to predict the precise form of the hue changes or the differences between the fovea and periphery. Our results suggest that a Gaussian model provides a useful heuristic for predicting constant hue loci and the form of the Abney effect at short and medium wavelengths and may approximate the inferences underlying the representation of hue in the visual system. (c) 2012 Optical Society of America

We are surrounded by a variety of color distributions, which change greatly according to the surrounding environment. It is not yet well understood hew much the appearance of objects is influenced by these color distributions in the surrounding environments. Brown and MacLeod (1997) showed that color appearance depends on the chromatic surround variance this is known as the "gamut expansion effect" However, Brown and MacLeod used relatively small patterns on a monitor. Whether the same effect would be obtained in an actual room environment has not been investigated. We examined whether the colorfulness perception of an object is influenced by the chromatic variance of its surroundings in a normal environment such as a room with furniture and objects inside. Two miniature rooms, one with gray and one with color-saturated objects inside, were placed side by side and used as a reference and a test room, respectively. Observers compared the colorfulness of a small square patch placed in the reference and the test rooms. The results showed that the apparent colorfulness colorfulness of a patch was generally lower when it was closely surrounded by color-saturated surfaces, suggesting that the odor appearance was changed slightly by the influence of other saturated objects in the room. However, the shift was very small, implying that chromatic surround variance has little influence on color appearance in an actual environment.

We examined how the distribution of colors in natural images varies as the seasons change. Images of natural outdoor scenes were acquired at locations in the Western Ghats, India, during monsoon and winter seasons and in the Sierra Nevada, USA, from spring to fall. The images were recorded with an RGB digital camera calibrated to yield estimates of the L, M, and S cone excitations and chromatic and luminance contrasts at each pixel. These were compared across time and location and were analyzed separately for regions of earth and sky. Seasonal climate changes alter both the average color in scenes and how the colors are distributed around the average. Arid periods are marked by a mean shift toward the +L pole of the L vs. M chromatic axis and a rotation in the color distributions away from the S vs. LM chromatic axis and toward an axis of bluish-yellowish variation, both primarily due to changes in vegetation. The form of the change was similar at the two locations suggesting that the color statistics of natural images undergo a characteristic pattern of temporal variation. We consider the implications of these changes for models of both visual sensitivity and color appearance.

Most wavelengths change hue when mixed with white light. These changes, known as the Abney effect, have been extensively studied to characterize nonlinearities in the neural coding of color, but their potential function remains obscure. We measured the Abney effect in a new way-by varying the bandwidth of the spectrum rather than mixing with white-and this leads to a new interpretation of the role of nonlinear responses in color appearance. Because of the eye's limited spectral sensitivity, increasing the bandwidth of a spectrum changes the relative responses in the three classes of cone receptor and thus would change hue if the percept were tied to a fixed cone ratio. However, we found that hue is largely independent of bandwidth and thus constant for a constant peak wavelength for stimuli with Gaussian spectra. This suggests that color appearance is compensated for the eye's spectral filtering, and that this compensation embodies specific perceptual inferences about how natural spectra vary. When a wavelength is instead diluted with white light-which does not bias the cone ratios-then the same compensation predicts changes in hue because the "right'' response is made to the "wrong'' stimulus. This model generates constant hue loci that are qualitatively consistent with measures of the Abney effect and provides a novel functional account of such effects in color appearance, in which postreceptoral responses are adjusted so that constant hue percepts are tied to consistent physical properties of the environment rather than consistent physiological properties such as the cone ratios.

The perception of blur in images can be strongly affected by prior adaptation to blurry images or by spatial induction from blurred surrounds. These contextual effects may play a role in calibrating visual responses for the spatial structure of luminance variations in images. We asked whether similar adjustments might also calibrate the visual system for spatial variations in color. Observers adjusted the amplitude spectra of luminance or chromatic images until they appeared correctly focused, and repeated these measurements either before or after adaptation to blurred or sharpened images or in the presence of blurred or sharpened surrounds. Prior adaptation induced large and distinct changes in perceived focus for both luminance and chromatic patterns, suggesting that luminance and chromatic mechanisms are both able to adjust to changes in the level of blur. However, judgments of focus were more variable for color, and unlike luminance there was little effect of surrounding spatial context on perceived blur. In additional measurements we explored the effects of adaptation on threshold contrast sensitivity for luminance and color. Adaptation to filtered noise with a 1/f spectrum characteristic of natural images strongly and selectively elevated thresholds at low spatial frequencies for both luminance and color, thus transforming the chromatic contrast sensitivity function from lowpass to nearly bandpass. These threshold changes were found to reflect interactions between different spatial scales that bias sensitivity against the lowest spatial grain in the image, and may reflect adaptation to different stimulus attributes than the attributes underlying judgments of image focus. Our results suggest that spatial sensitivity for variations in color can be strongly shaped by adaptation to the spatial structure of the stimulus, but point to dissociations in these visual adjustments both between luminance and color and different measures of spatial sensitivity.

After observers have adapted to an edge that is spatially blurred or sharpened, a focused edge appears too sharp or blurred, respectively. These adjustments to blur may play an important role in calibrating spatial sensitivity. We examined whether similar adjustments influence the perception of temporal edges, by measuring the appearance of a step change in the luminance of a uniform field after adapting to blurred or sharpened transitions. Stimuli were square-wave alternations (at 1 to 8 Hz) filtered by changing the slope of the amplitude spectrum. A two-alternative-forced-choice task was used to adjust the slope until it appeared as a step change, or until it matched the perceived transitions in a reference stimulus. Observers could accurately set the waveform to a square wave, but only at the slower alternation rates. However, these settings were strongly biased by prior adaptation to filtered stimuli, or when the stimuli were viewed within temporally filtered surrounds. Control experiments suggest that the latter induction effects result directly from the temporal blur and are not simply a consequence of brightness induction in the fields. These results suggest that adaptation and induction adjust visual coding so that images are focused not only in space but also in time. (c) 2005 Optical Society of America.

It is known that color constancy does not hold in a photograph. This could be because the photograph is recognized as a two-dimensional paper. Based on the concept of the recognized visual space of illumination (RVSI), it is predicted that color constancy holds in the photograph if it is perceived as a 3-D scene. We examined whether the color constancy held under a special viewing condition. A photograph of a room under incandescent illumination was shown under daylight illumination. We tested the neutral color perception of a stimulus on the photograph both with and without a dimension-up viewing box showing the photograph alone monocularly. The results showed good color constancy when a subject observed the photograph with the viewing box. It was also shown that the degree of color constancy decreased for a jumbled photograph without 3-D information. Our results suggest that the recognition of a space and illumination are important in color perception.

We used color contrast adaptation to examine the chromatic and contrast selectivity of central color mechanisms. Adaptation to a field whose color varies along a single axis of color space induces a selective loss in sensitivity to the adapting axis. The resulting changes in color appearance are consistent with mechanisms formed by different linear combinations of the cone signals. We asked whether the visual system could also adjust to higher-order variations in the adapting Stimulus, by adapting observers to interleaved variations along both the L versus M and the S versus LM cardinal axes. The perceived hue of test stimuli was then measured with an asymmetric matching task. Frequency analysis of the hue shifts revealed weak but systematic hue rotations away from each cardinal axis and toward the diagonal intermediate axes. Such shifts could arise if the adapted channels include mechanisms with narrow chromatic selectivity, as some physiological recordings suggest, but could also reflect how adaptation alters the contrast response function. In either case they imply the presence of more than two mechanisms within the chromatic plane. In a second set of measurements, we adapted to either the L versus M or the S versus LM axis alone and tested whether the changes in hue could be accounted for by changes in relative contrast along the two axes. For high contrasts the hue biases are larger than the contrast changes predict. This dissociation implies that the contrast and hue changes are not carried by a common underlying signal, and could arise if the contrast along a single color direction is encoded by more than one mechanism with different contrast sensitivities or if different subsets of channels encode contrast and hue. Such variations in contrast sensitivity are also consistent with physiological recordings of cortical neurons.

Face perception is fundamentally important for judging the characteristics of individuals, such as identification of their gender, age, ethnicity or expression. We asked how the perception of these characteristics is influenced by the set of faces that observers are exposed to. Previous studies have shown that the appearance of a face can be biased strongly after viewing an altered image of the face, and have suggested that these aftereffects reflect response changes in the neural mechanisms underlying object or face perception(1-5). Here we show that these adaptation effects are pronounced for natural variations in faces and for natural categorical judgements about faces. This suggests that adaptation may routinely influence face perception in normal viewing, and could have an important role in calibrating properties of face perception according to the subset of faces populating an individual's environment.

We recognize the outside world as a 3-D space in spite of its two-dimensional retinal image. We demonstrated a two-dimensional photograph could be perceived as a 3-D scene in a special 'dimension-up' viewing condition that a subject observed only the photograph. The color constancy was then realized in part even in the photograph and its degree increases depending on the degree of 3-D recognition. A jumbled photograph was made from an original photograph taken for a room under incandescent lamps. Either was on a wall of an experimental booth illuminated by white light. In the normal viewing condition, the subjects perceived neutral white for almost the same test stimulus whether in the original or the jumbled. In the dimension-up viewing condition, the shift of the neutral perception for the original photograph was larger than for the jumbled. This should indicate that the recognized visual space of illumination (RVSI) for the scene illuminated by incandescent lamps was constructed for the original photograph and the test stimulus was perceived as an object in the scene. The degree of the color constancy was larger in the photograph perceived as a 3-D scene than in that perceived as a mere two-dimensional scene.

Whenever we enter a space illuminated differently from a previous space whether in color or in illuminance, we can quickly adapt to the new atmosphere and can again perceive white for the originally white object this is known as color constancy. This phenomenon is explained by rotation of the recognition axis of the recognized visual space of illumination (RVSI) toward the illumination color. The explanation then predicts that the color appearance of a test patch changes radically toward the opposite direction from the color of illumination when the physical property of the test patch is kept unchanged at a neutral white. This prediction was confirmed by Experiment 1, where eight different colors of illumination were employed. The test patch appeared very vivid in color and shifted toward the opposite direction from the color of the illumination. In RVSI theory the light source color mode is explained by the release of the test patch from the restriction of RVSI. The release can be achieved by increasing the luminance of the test patch and the color appearance of the patch should then return to its own color as it is no longer controlled by RVSI. In Experiment 2 these predictions were investigated by increasing the luminance of the test patch to a much higher level than that of the objects in the lit room fixed at an illuminance of about 1001x. The color appearance of the test patch indeed became the light source color and returned to the original neutral white. Emphasis was given in the course of the experiments that the subjects were observing the test patch presented in a real 3D space where the subjects also stayed inside so that they could properly construct RVSI for the space.