Prediction of simultaneous contrast between map colors with Hunt's model of color appearance

The objective of this research was development of a quantitative model of simultaneous contrast (induction) to aid selection of sets of easily identified map colors. The model is an extension of R. W. G. Hunt's model of color appearance. Contrasts between central and proximal colors were used to adjust Hunt's lightness, relative redness-greenness, and relative yellowness-blueness measures. Human subject responses to CRT displays in an experiment were analyzed to produce a set of rules for selecting map colors. Rather than predict average perceptions for central/proximal color combinations, acknowledgment was made of the inherent variability in map readers' perceptions of color by developing generalized perception buffers that accounted for at least 90% of test subject responses. The task of selecting colors that will not be confused once they appear with numerous proximal colors on a map thus becomes a task of selecting colors that do not have buffers that overlap in color space. © 1996 John Wiley & Sons, Inc.     

Quantifying colour appearance. part III. Supplementary LUTCHI colour appearance data

The experimental data from this study supplements the LUTCHI Colour Appearance Data as described in Part I of this paper. Two further experiments were carried out: one was to check conflicting results found previously, and another was to extend the range of luminance conditions used earlier. In addition, a brightness attribute was added to the original lightness, colourfulness, and hue scales for colour assessment. Experiment I results verified the uncertainties found previously in the comparison between luminous and nonluminous colours, and between the grey background results with and without a white border. Experiment II results revealed the changes in four perceived attributes under six quite different adapting luminances. The results were then used to test five uniform colour spaces and colour-appearance models used in Part II of this paper. Hunt's 91 model gave more accurate predictions of the experimental visual results, in comparison with the other spaces and models. Its predictive error for all attributes studied is within the accuracy of the typical observer.     

Quantifying colour appearance. part IV. Transmissive media

The experimental data from this study extends the LUTCHI colour-appearance data to cover transmissive media. Two further experiments were carried out: one used a large cut-sheet transparency viewed using a back-lit illuminator, and another used a 35-mm slide projected onto a white screen. These new data were used to reveal the changes in colour appearance caused by different viewing parameters studied, and to evaluate the predictive accuracy of five uniform colour spaces and colour-appearance models. The results show that Hunt's 91 model (developed to fit earlier experimental results) did not perform as well as it did in the previous studies using nontransmissive media. This implies that there are large differences in perceived colour appearance between transmissive and nontransmissive media viewing conditions. Some modifications were subsequently made to Hunt's 91 model and the predictive accuracy was greatly improved.     

Quantifying colour appearance. Part I. Lutchi colour appearance data

The work described here forms part of a research project entitled Predictive Perceptual Colour Models. The aim of this project is to develop a colour appearance model capable of predicting changes of colour appearance under various different viewing conditions. This will provide industry with a quantitative measure for assessing the quality of colour reproduction and enable more rapid and accurate proofing simulations in the graphic art industry. A large-scale experiment has been carried out in which colour appearance was assessed under a wide range of viewing conditions. The parameters studied were (1) D65, D50, white fluorescent, and tungsten light sources, (2) luminance levels of about 40 and 240 cd/m², (3) five background conditions: white, grey, black, grey with white border, and grey with black border, and (4) two media: luminous colours (displayed on a high-resolution colour monitor) and nonluminous colours (presented in a viewing cabinet). Each colour was assessed by a panel of six or seven observers using a magnitude estimation method. In total, 43,332 estimations were made, and these form the LUTCHI Colour Appearance Data. Data analysis has been carried out to examine the reliability of the experimental results and to understand the effects of the various viewing parameters studied. (Part II of this article describes how the LUTCHI Colour Appearance Data has been used to test the performance of various colour spaces and models.     

Michel‐Eugène Chevreul: From laws and principles to the production of colour plates

Michel‐Eugène Chevreul (1786–1889) did major scientific work in the fields of chemistry and colour and pioneered the study of simultaneous contrast. His book De la loi du contraste simultané des couleurs (The Principles of Harmony and Contrast of Colours) was published in 1839. Here, his studies pertained to simultaneous contrast, when two or more colours seen contiguously are influenced in brightness and/or in hue, and on successive contrast, when afterimages modify colour perception. He also investigated the mixed contrast that appeared in tapestries in which a mixture of colours was obtained by the plying of yarn or by hatching. Later, he reported on the influence exerted on vision by coloured objects in circular motion around an axis perpendicular to their plane (1879). Many examples and numerous experimental checks documented in his books supported his demonstration of contrast. Of particular interest are the colour plates attached to the books. Another significant work by Chevreul was a three‐dimensional colour classification system (1864), after which he manufactured a colour atlas showing colour circles and monochrome lightness scales. Data are presented from recent measurements of Chevreul's atlas circles and plates, and there is a discussion of his choice of complementary colours. © 2002 John Wiley & Sons, Inc. Col Res Appl, 27, 4–14, 2002     

Evaluating colour models' performance between monitor and print images

The earlier experimental results (Color Res. Appl. 16, 166–180, 181–197; 18, 98–113, 191–209; 20, 18–28) have been further extended to include data obtained using complex images. Binocular memory and simultaneous matching techniques were used to assess the colour reproduction quality of displayed monitor images processed via eight colour models against a hardcopy (original) image illuminated in a viewing cabinet. The results from a panel of nine observers were used to compare different colour models' performance. It was found that the BFD chromatic adaptation transform outperformed the other models. The Hunt94 model, which gave a good fit to the earlier results, did not perform well. This indicates that there are differences in colour appearance between the complex and simple viewing fields. Other aspects were also investigated such as observer precision and repeatability, spatial uniformity of the monitor, image dependency, and the difference between the category judgment and paired comparison results. © 1996 John Wiley & Sons, Inc.     

Effective and efficient mapping of color appearance

The reproduction of color across different media and viewing condition requires color-appearance modeling. In order to obtain an effective and efficient mapping of color appearance, the authors define here a method to approximate the combination of the forward and reverse Hunt94 color-appearance models. The method consists in learning by examples the Hunt94 color mapping for each desired experimental setup. Learning is done by feed-forward neural networks trained with the back-propagation algorithm on training sets derived from the ANSI IT8 7.2 color target. Experimental results confirm the feasibility of the method. © 1997 John Wiley & Sons, Inc. Col Res Appl, 22, 308–317, 1997.     

Visual clarity and feeling of contrast

The visual clarity of a lighting environment is significantly affected by changing the general color rendering index (Ra) of its illumination. This effect has been studied by a number of researchers, but the cause of this effect has not been thoroughly studied. In order to clarify this, the mutual relations between visual clarity, lightness perception, and feeling of contrast are analyzed by using object colors under illuminations with various Ra values. the results obtained are as follows. (1) the visual clarity of a lighting environment is different from the lightness perception of the object colors in the environment. (2) the change in visual clarity of a lighting environment is highly correlated to a feeling of contrast between object colors under the illumination. (3) the effect of visual clarity is estimated effectively by assessing the feeling of contrast using a specially selected four-color combination. (4) the illuminance for equal visual clarity for any illumination is predicted by the equality of feeling of contrast under the same illumination specified by the gamut area made by the component colors of the four-color combination in a brightness and colorfulness space. (5) the effect of visual clarity under various illuminations cannot be predicted by using their Ra values.     

Observation and measurement of the appearance of metallic materials. Part I. Macro appearance

The use and characterization of metallic paints and plastics have been important, particularly in the automotive industry, throughout the last half of this century. The scientific concepts and terminology of this field are still evolving. The principal appearance characteristics of these materials, when viewed at a distance, are luster and goniochromism. Methods of characterizing and measuring metallic surfaces are being standardized by a committee of the American Society for Testing and Materials. New instrumentation has been developed to provide controlled viewing conditions for judging these materials. Modern portable multi-angle measuring instruments are easy to operate and take measurements very quickly. © 1996 John Wiley & Sons, Inc.     

Experimental object color unique hue data for the mean observer for color appearance modeling

Color appearance models, among other things, predict the hue of a stimulus when compared with defined stimuli that represent the four unique hues. Recent studies have indicated that the stimuli representing with high reliability unique hue (UH) percepts vary widely for different color‐normal observers. The average yellow and blue UH stimuli for 102 observers, as determined in a recent experiment at medium chroma, differ considerably from the CIECAM02 defined unique hues, based on the Swedish NCS. Wide inter‐observer variability precludes color appearance models from accurately predicting, for individual observers, all four unique hue stimuli. However, models should predict accurately those of a well‐defined average observer. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 505–506, 2008     

Determination of constant Hue Loci for a CRT gamut and their predictions using color appearance spaces

A colorimetrically characterized computer-controlled CRT display was used to determine 24 loci of constant perceived hue for pseudo-object related stimuli, sampling the display's interior color gamut at constant lightness and the edge of its gamut at variable lightness. Nine observers performed three replications generating matching data at 132 positions. the constant hue loci were used to evaluate the correlation between perceived hue and hue angle of CIELAB, CIELUV, Hunt, and Nayatani color appearance spaces. the CIELAB, CIELUV, and Hunt spaces exhibited large errors in the region of the blue CRT primary, while the Nayatani and CIELUV spaces produced large errors in the region of the red primary for constant lightness stimuli. Along the edge of the CRT's color gamut (variable lightness stimuli), all the spaces had a similar trend, large errors in the cyan region. the differences in performance between the four spaces were not statistically significant for the constant lightness stimuli. For the variable lightness stimuli, CIELAB and CIELUV had statistically superior performance in comparison with the Nayatani space and equal performance in comparison with the Hunt space. It was concluded that for imaging applications, a new color appearance space needs to be developed that will produce small hue error artifacts when used for gamut mapping along loci of constant hue angle. © 1995 John Wiley & Sons, Inc.     

The relationship between visual acuity and color contrast in the OSA uniform color space

OSA uniform color space was used to study the relationship between visual acuity and OSA color contrast. Visual acuity is characterized by 50% minimal separable visual angle using Landolt-C. The OSA color contrast is characterized by the distance between colors in OSA color space. Twenty subjects with normal color vision were tested on 342 test sheets printed with colored Landolt-Cs and background. These results demonstrated that MSVA is approximately inverse log-linearly related to OSA color contrast (R² = 80.4%). Although luminance contrast (R² = 54.2%) is more salient than chromatic contrast (R² = 16.4%), both contrasts can induce very high visual acuity provided that they are sufficiently high. There is also evidence of an additive interaction between chromatic contrast and luminance contrast. Based on these findings, the OSA uniform color space and its color difference formula can be used as a scale for quantifying color contrast to accurately predict the size of colored text or symbols. © 1996 John Wiley & Sons, Inc.