Background Lightness Research Articles

Appearance variations of textile materials due to different near gray backgrounds

AbstractThe preliminary experiments were carried out for investigating the effect of lightness of achromatic background (white, grays, and black) on color appearance attributes (lightness and colorfulness) of some colored fabrics. A series of achromatic backgrounds at eight levels of lightness was provided. Each test color was viewed against these backgrounds and the perceived lightness and colorfulness were evaluated by using the pair comparison method.The results indicated that the lightness of achromatic background affects perceived lightness and colorfulness. The lightness of tests colors increases when surrounded by dark backgrounds while a consistent trend was not noticed for perceived colorfulness. The results from visual assessment were compared with the predicted results by the CIECAM97s model. The predictions of the model were in agreement with the perceived lightness by visual assessment but there was not any correlation between the results of model and visual assessment for colorfulness.In the second part of the experiments, a colorimetric match of samples on different backgrounds was carried out by visual judgments as well as implementation of color appearance models in reverse mode. Results from visual trials were significantly different from those predicted by the models. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 133–141, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20190

Colour constancy in goldfish and man: influence of surround size and lightness.

Colour constancy was investigated by using a series of 10 simultaneously presented surface colours ranging in small steps from green through gray to red-purple. Goldfish were trained to select one medium test field when the entire setup was illuminated with white light. In the tests, either red or green illumination was used. Colour constancy, as inferred from the choice behaviour, was perfect under green illumination when the test fields were presented on a gray or a white background, but imperfect on a black background. Under red illumination and a white background, however, colour constancy was overcompensated. Here, a colour contrast effect was observed. The influence of background lightness was also found when the surround was restricted to a narrow annulus of 4-11 mm width (test field diameter: 14 mm). By applying colour metrics it could be shown that the von Kries coefficient law can describe the overall effect of colour constancy. For an explanation of the effect of surround size and lightness, lateral inhibitory interactions have to be assumed in addition, which are also responsible for simultaneous colour contrast. Very similar results were obtained in experiments with the same colours in human subjects. They had to name the test field appearing 'neutral' under the different illumination and surround conditions, as tested in the goldfish experiment.

Investigation of parametric effects using large colour differences

Sixty-five wool sample pairs around eight colour centers were used to investigate the change of colour differences caused by four viewing parameters: lightness of background, sample separation, luminance, and magnitude of colour difference. The average size of colour difference was 13 CIELAB ΔE units. Each pair was assessed 20 times by a panel of 13 normal colour-vision observers using the gray scale psychophysical method. The viewing parameters investigated did not greatly affect the perceived colour difference. The largest discrepancy was found between the gray and white background conditions, i.e., the same pair of samples shows a 30% larger colour difference against a white background than against a gray background. The present results were also used to compare with those of the authors' earlier study2 using small colour differences. It showed that there is a large difference in characteristics between the large and small colour differences. The visual data were also used to test five colour-difference formulae: CIELAB, CMC, BFD, CIE94, and GLAB. The results showed that the GLAB formula, developed by the authors, performed marginally better than the other formulae. © 1999 John Wiley & Sons, Inc. Col Res Appl, 24, 356–368, 1999

Ergonomic requirements for reflective liquid-crystal displays

We investigated the ergonomic requirements for lightness, contrast and character size of reflective liquid-crystal displays (LCDs) for young and aged users. The 30 young subjects (mean age: 21.3 yr) and 24 older subjects (mean age: 58.6 yr) subjectively rated 25 combinations of lightness and contrast for five character sizes displayed on hard copies that simulated reflective LCDs. The results indicate that the character size should be 15 point (pt) when the characters are viewed at a distance of 40 to 50 cm and at an inclination angle of about 40°. The required contrast depends on the background lightness. When the background lightness L* is 70, the required contrast ( L max/ L min) is about 4 for 15 pt characters, whereas a contrast of 6 or 7 is required when L* is 50. These requirements for the 15 pt characters are common to both the young and older subjects. When the character size is smaller than 15 pt, however, the older subjects required a very high lightness and contrast compared with the younger subjects.

反射型液晶ディスプレイに要求される文字表示条件 ユーザの年齢による違い

We investigate the ergonomic requirements for lightness, contrast and character size of reflective liquid crystal displays (LCDs) for young and old users. The 30 young subjects (mean age : 21.3) and 24 old subjects (mean age : 58.6) rated 25 lightness and contrast combinations for five character sizes displayed on hard copies that simulated reflective LCDs. The results indicate that the character size required is 15 point when the characters are viewing at a distance of 40 or 50 cm and an inclination angle of about 40 degrees. The required contrast ratio depends on the background lightness. When the background lightness L* is 70, the required contrast ratio is about 4 for the 15-point characters. When the background lightness is 50, however, the contrast required is 6 or 7. These requirements are almost the same for young and old subjects. When the character size is smaller than 15 point, however, old subjects require very high lightness and contrast compared to young subjects. This difference may be due to age-related differences in the visual acuity for close targets.

反射型液晶ディスプレイに要求される文字表示条件

Abstract We investigated the ergonomic requirements for lightness, contrast and character size of reflective liquid-crystal displays (LCDs) for young and aged users. The 30 young subjects (mean age: 21.3 yr) and 24 older subjects (mean age: 58.6 yr) subjectively rated 25 combinations of lightness and contrast for five character sizes displayed on hard copies that simulated reflective LCDs. The results indicate that the character size should be 15 point (pt) when the characters are viewed at a distance of 40 to 50 cm and at an inclination angle of about 40°. The required contrast depends on the background lightness. When the background lightness L* is 70, the required contrast (Lmax/Lmin) is about 4 for 15 pt characters, whereas a contrast of 6 or 7 is required when L* is 50. These requirements for the 15 pt characters are common to both the young and older subjects. When the character size is smaller than 15 pt, however, the older subjects required a very high lightness and contrast compared with the younger subjects.

Factors Affecting the Appearance of Coloured Images on a Video Display Monitor*

AbstractThis paper summarizes the findings of a three-year research project into the factors affecting the colour appearance of complex images on different media and under different viewing conditions. A series of experiments was conducted, with observers using the magnitude estimation technique to scale the lightness, colourfulness and hue of a sequence of coloured test patches in a complex field. The parameters studied included the type of illuminant, level of illumination, lightness of background, and medium (luminous colours were displayed on a high-resolution colour monitor and non-luminous colours were presented as patches on white, grey and black cards in a viewing cabinet). A mathematical model, based on that developed by Hunt, was shown to perform better in predicting colour appearance under a variety of viewing conditions than any other known model. Further experiments investigated the effect of chromatic induction on colour appearance, by varying the lightness, colourfulness and hue of an induc...

Achromatic color matching as a function of apparent target orientation, target and background luminance, and lightness or brightness instructions.

In two experiments, achromatic color matches for a fixed target, under constant illumination, were compared under conditions where the target appeared perpendicular to illumination direction and coplanar with the background (monocular viewing) and where the target appeared nonperpendicular to illumination direction and noncoplanar with the background (binocular viewing). Contrary to the coplanar ratio hypothesis, which predicts a “lightening” of the target seen coplanar with a darker background, a general “darkening” of the target occurred for both white (N9.5/) and black (N3/) backgrounds and for both dark (N5.5/) and light (N6.5/) targets. This darkening effect was greatest for the darker target and black background, and approximately equal for other combinations of target value and background. The direction of the darkening effect is consistent with the albedo hypothesis, which assumes an inferential correction for changes in conditions of illumination. However, variation in the magnitude of the darkening effect is problematical, and cannot be easily explained by any existing theory. In both experiments, instructions to judge “lightness” or “brightness” failed to produce any substantial differences in performance, although postexperimental questioning suggested that subjects had a verbal understanding of these concepts. Apparently, under reduction conditions, subjects lack cues to illumination and make only lightness matches, regardless of instructions.

Contrast and assimilation in lightness judgments

Experiments studied how assimilation and contrast varied as a function of the reflectance of figures above and below the reflectance of a gray background. The results showed that for the experimental conditions investigated: (a) contrast always occurs when the reflectance of lines is above the reflectance of the background, (b) assimilation occurs when the reflectance is below that of the background, (c) circles produce the same degree of assimilation and contrast as lines of equal width, and (d) repeated judgments do not affect contrast but reduce assimilation; as line darkness and line width increase assimilation gives way to contrastfollowing repeated judgments. The results are discussed in connection with the hypothesis that assimilation and contrast arisefrom opponent processes in the visual system. Helson (1964) investigated the changes produced in the lightness of a gray background by the presence of black and white lines. He found that lightness changes went from assimilation (the darkening of the gray back­ ground by the black lines or the lightening of it by white lines) to contrast (the darkening of the gray by white lines or the lightening of it by black lines) as a function of line width, line separation, and the reflectance of the background. This findingsuggestedthatassimila­ tion and contrast arise from opponent processes that depend on the differences in stimulation in contiguous areas. Helson hypothesized that small differences in stimulation in neighboring areas result in summation, producing assimilation, and that large differences result in inhibition, producing contrast. The purpose of the present study was to investigate the phenomena of assimilation and contrast as a function of 'le reflectance of figures above and below the reflectance of a gray background. Three experiments were performed to examine whether the size of the difference in stimulation alone does in fact determine if assimilation or contrast will occur. EXPERIMENTS I AND II Experiments I and II compare the lightness judgments of a gray background when the reflectance of lines and circles was varied'.