Walls Surrounding a Space Work More Efficiently Construct a Recognized Visual Space of Illumination than Do Scattered Objects

The apparent color of an object depends on how we recognize the space where it is placed in terms of illumination. We call this the recognized visual space of illumination (RVSI). What we see in the space first, namely, the initial visual information (IVI) determines properties of the RVSI, and we will show in this paper that the walls surrounding this space are the most important IVI for the construction of the RVSI. A normal room was illuminated by a ceiling light at 60 lx and its central area was also lit by a hidden illumination of 400 lx. Two halves of a miniature room with walls on three sides and a floor were inserted from left and right sides into the hidden illumination to gradually create one miniature room, and the apparent lightness of a test patch was judged as a function of the amount of the inserted portions to measure construction of RVSI for the hidden illumination. The apparent lightness was around 55 in L∗ when no IVI was in the hidden illumination, it gradually went down with more IVI to around 40 L∗ to return toward its nominal lightness of 24 L∗ in the case of test patch N2. The drop was large with the present condition of IVI where, in the end, the space of the hidden illumination was surrounded by walls, compared to the previous results where the space was filled only by objects; this indicated the importance and efficiency of walls for constructing RVSI.     

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.     

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.     

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 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.     

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.     

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.     

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.     

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.     

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 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 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.     

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     

CIELAB与CIECAM02色空间均匀性比较研究

采用均匀色空间Munsell系统检验和验证了CIELAB和色貌模型CIECAM02色空间的均匀性。利用Mun- sell色卡所对应的三刺激值X,Y,Z作为模型的输入值,预测色空间模型的明度、彩度和色调,并通过预测结果比较和检验了CIELAB色空间和CIECAM02模型色空间的均匀性。研究表明:在预测明度方面,两个色空间的结果相似;在预测彩度时,CIECAM02模型较好于CIELAB色空间;在预测色调时,当色调逐渐从BG变化到B时,CIELAB所预测的色调角与由Munsell色空间计算出来的色调角之差逐渐增大,最大时超过6%,而CIECAM02所预测的色调角与Munsell色空间的色调角之差在2.5%以内,CIECAM02优于CIELAB色空间。     

光照光谱功率分布的估计和颜色分割

提出了应用有限维线性模型和双色反射模型和双色反射模型抽表示而物体颜色的本征特性的方法，首先估计出光照的光谱功率分布，再获取物体的表面光谱反射率，从而得到和光照与几何条件无关的归一化偏差光谱反射率，它仅反映物体的表面反射特性，可作为颜色分割和识别的可靠特征。     

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.     

颜色视觉匹配中明度阈值的评价

为了对颜色视觉匹配中的明度阈值特性进行评价,采用在阴极射线管显示器上获得的颜色刺激,在5个不同明度的中性色背景下,标准刺激的明度L*从5到95以5个CIELAB单位为变化步长,共对19个不同明度的中性标准颜色进行视觉匹配实验。通过对实验结果的处理和分析,验证了关于颜色刺激视觉辨别明度阈值与背景明度之间相关性的韦伯法则和crispening效应,同时利用颜色视觉匹配数据对基于CIELAB的相关色差公式进行了评价和比较,CIEDE2000具有最好的明度差预测性能,CMC次之,CIELAB和CIE94最差。     

Lightness and chroma enhancement for food images considering Helmholtz–Kohlrausch effect

The color appearance of a food image is very important for making it look delicious. Many food images acquired in low illumination environments do not give delicious impressions because of the deterioration of their color appearance. We propose an image enhancement method to improve the color appearance of a food image acquired in a low illumination environment. In the proposed method, the lightness of each pixel is first enhanced within a color gamut on an equal hue plane in the CIELAB color space. The boundary of the color gamut is given by a lookup table calculated in advance. Then, when the hue of the pixel is attributed to foods, the chroma is enhanced within the color gamut. In this case, we consider Helmholtz–Kohlrausch (H-K) effect, which indicates the relation of the hue, chroma, and lightness in human visual perception. According to H-K effect, the perceived lightness increases as the chroma is enhanced. Therefore, the perceived lightness is preserved after the chroma enhancement, so that the food image is not too enhanced. To verify the effectiveness of the proposed method, experiments are conducted using several food images.     

基于数码相机的闪光灯投射系统照度分布测试

数码相机通过将景物取样成一系列像素来记录景物,而且每个像素的亮度取决于景物接收的光通量———照度。基于这一原理进行了闪光灯投影系统照度分布测试实验。首先通过数码相机采集被照物面的灰度图,然后用Photoshop图像处理软件和Matlab软件对图片进行量化分析处理,最终得到了闪光灯投射系统的照度分布情况。该测试方法简单、新颖,测试精度可满足工程应用需要。