Color Appearance Explained,Predicted and Confirmed by the Concept of Recognized Visual Space of Illumination

Ten years have passed since we proposed a new concept called recognized visual space of illumination (RVSI). The central idea of the concept assumes that our brain first recognizes how a space is illuminated and then judges colors of anything seen in the space in relation to the RVSI constructed for the space. In another expression we say that the space is recognized first and the color perception next. In this paper some of our experiments that proved the appropriateness of the concept will be introduced. When a white paper was seen through a colored filter we could perceive the paper as white at the same instant we recognized a space through and beyond the filter. When an achromatic patch independent from the room illumination was observed under colored illumination its appearance immediately changed to that roughly opponent to the illumination color. When two gray patches of the same lightness were drawn in a picture of a white grating on a black background on a way that one appeared to locate on this side of the grating and the other in the other side, the former appeared brighter. These all confirmed the predictions based on the RVSI concept.     

Phenomena of Apparent Lightness Interpreted by the Recognized Visual Space of Illumination

Many experimental results have been reported which demonstrated deviation of the apparent lightness from the calculated lightness based on spectral reflectance, and these have caused debate among researchers as to the models to explain them. The judgement of lightness of objects that we see in the outside world is one of the most important tasks in our daily life. We proposed the recognized visual space of illumination, RVSI, as a three dimensional recognition constructed in the brain for the outside world, and showed that the apparent lightness was determined in relation to the size of the RVSI. In the present paper the concept was applied to various results of lightness experiments such as the White effect and simultaneous contrast, and based on the proposition that an observer first builds a three dimensional RVSI from a two dimensional pattern and the lightness of a test patch was judged in relation to the size of this RVSI, the results were then globally and nicely explained. A new demonstration of a pattern was proposed to give different apparent lightness for patches with the same physical lightness to strengthen the proposition. The importance of distinguishing between a test patch and a surrounding field was emphasized when one does a lightness experiment and interprets the results.     

Lightness Change as Perceived in Relation to the Size of Recognized Visual Space of Illumination

According to the concept of the recognized visual space of illumination (RVSI) the lightness of an object surface is perceived in relation to its conceptualized size. To prove this proposition the lightness of gray test patches was judged when they were located at various positions inside an illuminated space composed of two rooms in the depth direction from a subject. No retinal image arrangement was changed in the test patch and its immediate surroundings, but the front room had walls, floors and furniture lower in lightness by the amount of N1.5 than the back room to make the RVSI of the former smaller despite the illuminance in the entire space being the same. The results showed that the apparent lightness of the patches was perceived higher by amount of about 13 in L units for the N4 test patch and about 20 for N6 when the patches were located in the front room, in accordance with the prediction. It was stressed that the experiment of lightness judgment should be conducted in a three dimensional space rather than two dimensional plane as done by several investigators.     

Three Dimensionality of the Recognized Visual Space of Illumination Proved by Hidden Illumination

We hypothesized that the recognized visual space of illumination (RVSI) was constructed in our brain when we grasped the state of illumination of a space. The importance about the RVSI is that it is three dimensional and is valid not only at the surfaces of the existing objects in the space, but also for the entire portion in the space where no objects exist. With this property of RVSI we are able to predict the appearance of an object surface in terms of lightness as well as of color when the object shifts from one place to the other in the space. The three dimensionality of the RVSI is proved by giving a hidden illumination within a space and by asking a subject to judge the lightness or color of a test patch placed in the area of the hidden illumination. In spite of the additional light on the test patch the subject did not recognize that the light was added but simply felt that the surface was made of a higher lightness or colored by transferring the light into an increase of the reflectance factor of the test patch. The results can be interpreted if we assume that a same RVSI exists throughout the entire space including the area of the hidden illumination.     

Color Property of the Recognized Visual Space of Illumination Controlled by Interior Color as the Initial Visual Information

It was shown that the color property of the recognized visual space of illumination, RVSI was controlled by changing the initial visual information by arranging objects in the room all shifting toward orange direction. We constructed two miniature rooms, D and I, both illuminated by the same daylight type fluorescent lamps but arranged with furniture of different color, those in room I shifting toward color as if they were illuminated by an incandescent lamp. Subjects felt as if room I were illuminated by an incandescent lamp. A test patch was placed midair in each room and its color was judged. When the test patches were placed in room I their colors were all perceived to be shifted toward greenish blue compared to those of test patches placed in room D, in spite of having the same illumination. The results imply that the apparent color of an object is determined not by its chromaticity, but in relation to the color property of the RVSI of the room where the object is observed.     

The Brain Adaptation to the Color of Illumination and not the Retinal Adaptation to the Color of Objects that Determines the Color Appearance of an Object in the Space

Color appearance was measured for a test patch which was placed in a test room illuminated by the daylight type of illumination and was looked at from the subject room illuminated by one of the four colored illuminations, red, yellow, green, and blue, through a window of three different sizes. When the window was the smallest so that only the test patch was seen within the window the color of the test patch appeared almost opponent to the illumination color, but as soon as something is seen within the window of larger size the color returned to the original color of the test patch to indicate the color constancy. To recognize the test room as a space was essential to perceive the real color of the test patch. This returning to the original colors was not influenced by green color of objects densely placed in the test room or by red color of objects again densely placed in the test room. The results imply that the color appearance of the test patch is not determined by the retinal chromatic adaptation, but by the brain adaptation to color of the illumination in the space.     

Color Appearance Determined by Recognition of Space

The color appearance was measured for a test patch which was placed in a test room illuminated by daylight lamps and was looked at from a subject room illuminated by one of four colored illuminations, red, yellow, green and blue, through windows of various sizes. When the window was small so that only the test patch was seen within the window the color of the test patch appeared almost opponent to the illumination color, but as soon as something was seen within the window of a larger size the color returned to the original color of the test patch. To recognize the test room as a space was essential to perceive the real color of the test patch. The results were explained by the concept of the recognized visual space of illumination.     

Color Constancy in a Photograph Perceived as a Three-Dimensional Space

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.     

Failure of color constancy for high luminance of a test patch that appears unnatural as an object in a space

The theory of the recognized visual space of illumination (RVSI) is that the color appearance of objects in a space is determined in relation to its recognition axis RX whose direction is determined by the brain action to adapt to the illumination in the space. Thus the color constancy holds. RX is applicable to objects in the space but not to an object or a portion that does not belong in the space in terms of illumination, that is to say, the luminance of which is too high based on the illumination for that space. In that case the color appearance would be determined in relation to the fundamental axis FX and the color constancy would not hold. In the present paper the chromaticity points were measured for a test patch that appeared achromatic for various luminance of the patch. The points were close to the color of illumination to indicate the color constancy when the luminance was low enough to assure its appearance as the object color, but they departed from the color of illumination and approached the colorimetrically achromatic color. The color constancy gradually failed for the test patch with the high luminance when the color mode became an unnatural object color and then a light color.     

Effect of Space Recognition on the Apparent Lightness of Gray Patches Demonstrated on Printed Patterns

The retinal image of the outside world is two dimensional and the brain automatically transfers the 2D image to 3D space in order that a human can recognize the world correctly. A printed black and white picture of a grating or a cube was presented to subjects through a viewing box to exclude other objects than the pattern so that the brain was provided with only the information about the pattern and recognized a 3D space for the pattern efficiently. Once a space recognition was achieved there was constructed a recognized visual space of illumination (RVSI) which controlled the apparent lightness of gray patches drawn in the picture. In the grating experiment the apparent lightness of a gray stimulus drawn as if it were located on this side of the white stripes, was shown to become lower than that of a gray reference stimulus drawn behind the white stripes with black background when both stimuli had the same lightness. Similarly, in the cube experiment the apparent lightness of a gray stimulus drawn way behind the white cube was shown to become lower than that of a gray reference stimulus drawn over black stripes that lay on the cube. The amount of these space recognition effects on apparent lightness was about 0.5 in Munsell Value when measured by brightness matching between the test and the reference stimulus.     

Color Appearance of a Patch Explained by RVSI for the Conditions of Various Colors of Room Illumination and of Various Luminance Levels of the Patch

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.     

Color Modification of Pictures Requiring Same Color Impression as Real Scene

Color constancy is an important feature of the human visual system. Our visual system adapts almost instantly to new illumination and we can perceive the color of objects in a new space correctly whatever color the illumination may be. This feature is not solely that of a commercially available camera. The difference between the human visual system and a camera raises a problem in our observation of pictures. We cannot see the exact color that a photographer intended to show us through a picture. Some color modification must be made to the picture to resolve this. In the present paper, the degree of modification was determined for various color combinations of illumination for taking a picture, FL_L and observing the picture, FL_o. An entire experiment was carried out in an actual room based on the belief that color appearance of objects is determined in relation to the recognized visual space of illumination (RVSI). A subject observed the color of a room lit by FL_L and pictures of the room lit by various colors of FL_L were taken. The pictures were displayed in another room lit by FL_o and the subject chose the picture that gave him/her the same color impression as the room of FL_L. In the case of picture slide, the color of the picture must be modified as if it were taken with the illumination inbetween the color of FL_L and FL_o. In the case of picture print, a similar modification was needed for reddish FL_L and white FL_O, but it was not needed for white FL_L and reddish FL_o.     

Color appearance seen through a colored filter of various sizes

It will provide us an effective method to study the color perception of the elderly if we can employ for young subjects a pair of glasses with color property chosen to simulate that of the elderly. One problem has to be solved before using such glasses based on the concept of the recognized visual space of illumination, that is, the size of the glasses. When a piece of a white paper is seen through a yellow filter in a room, it naturally appears yellowish. But if the observer uses the filter to cover his/her eyes entirely the white paper returns to its original white; this is known as color constancy. Between these two extreme cases, the color is expected to change from yellow to white. Chromaticness and hue of an achromatic test chart of a small or large size were determined by the elementary color naming method when the chart was seen monocularly through a red, yellow, green or blue filter, respectively, placed at various distances from the eyes. Chromaticness was large at around 40% when the visual field through the filter was equal to or smaller than the test chart, but it rapidly decreased when the visual field extended over the test chart so that objects other than the test chart were included in the visual field. It decreased to almost zero when the filter was about 5 cm or less away from the eye. It was concluded that we do not necessarily have to use goggles to cover the entire visual field but can use a normal pair of glasses made of colored filters for young subjects to study the color perception of the elderly with understanding that the study is only for the color perception experienced while wearing the glasses.     

Room Illuminance rather than Immediate Surrounding Luminance Determines Natural to Unnatural Color of an Object Border

The color of an object placed in a room goes through various modes of color appearance if its luminance is increased independently from the room illumination; from the natural object color to an unnatural object color, and to the light source color having two borders. We were interested in investigating the determining factor for the first border as it is useful in lighting design. It has been thought without a specific theory that it is the surrounding luminance that determines the border. According to a new concept of the recognized visual space of illumination (RVSI), the border is solely determined by the room illumination, and not by the luminance of the immediate surroundings of the object. In the first experiment of the present paper the border of a test stimulus was determined for various room illuminance while keeping the luminance of the immediate surroundings constant. It was shown that the border luminance was roughly proportional to the room illuminance, confirming the prediction based on the RVSI theory. In the second experiment the border was determined for varying luminance of the immediate surroundings while maintaining constant room illuminance. The border did not change, again confirming the prediction based on this theory.     

Size Effect of the Immediate Surround for the Border between the Natural and Unnatural Object Color Appearance

The border luminance of the test stimulus between the natural and unnatural object color, y_ynB_u was obtained for different spatial sizes of the immediate surround to prove that _nB_u can be determined based on a new recognized visual space of illumination (RVSI) that is assumed to be constructed for the immediate surround separately from the RVSI for the subjects room itself. The _nB_u of five test stimuli were determined for six different sizes covering from zero to 1866 cm² with four different lightnesses, N4, N6 and N8, while keeping the room illuminance constant at 100 or 600 lx. The results showed that luminance of the border _nB_u gradually decreased as the size of the immediate surround was increased and that the decrease was larger for immediate surround with lower lightness. The results were interpreted as showing a new RVSI constructed for the spatial extent of the immediate surround of the test stimulus, and the RVSI was more completely constructed for larger spatial size of the immediate surround. © 2005 The Optical Society of Japan