Crispening Effect Research Articles

Geometry of color perception. Part 1: structures and metrics of a homogeneous color space

This is the first half of a two-part paper dealing with the geometry of color perception. Here we analyze in detail the seminal 1974 work by H.L. Resnikoff, who showed that there are only two possible geometric structures and Riemannian metrics on the perceived color space mathcal{P} compatible with the set of Schrödinger’s axioms completed with the hypothesis of homogeneity. We recast Resnikoff’s model into a more modern colorimetric setting, provide a much simpler proof of the main result of the original paper, and motivate the need of psychophysical experiments to confute or confirm the linearity of background transformations, which act transitively on mathcal{P} . Finally, we show that the Riemannian metrics singled out by Resnikoff through an axiom on invariance under background transformations are not compatible with the crispening effect, thus motivating the need of further research about perceptual color metrics.

Color Perception of the Observer with the Manifestation of the Chromatic Effect of Crispening

This research presents the results of the appearance of chromatic effect of crispening on a designer solution in which the primary stimuli are made in the purple color with the values of 55% RTV and 65% RTV and backgrounds are made in the green-blue color, and their variations are designed in the values of 25% RTV, 50% RTV, 75% RTV and 100% RTV that are placed around the primary stimuli. The test subjects (n=10) that took part in the research had the task to equalize the test primary stimuli with the referential stimuli on a computer screen with the help of the technique of simultaneous binocular harmonization. The strength of the crispening effect was defined and shown in the CIEDE00 system. The conclusion of the conducted tests indicates that the intensity of crispening was stronger on the test primary stimuli 65% RTV, where the differences in the perception of color were more significant.

Perceptual dimensions underlying lightness perception in homogeneous center-surround displays.

Lightness judgments of targets embedded in a homogeneous surround exhibit abrupt steps in perceived lightness at points at which the targets transition from being increments to decrements. This "crispening effect" and the general difficulty of matching low-contrast targets embedded in homogeneous surrounds suggest that a second perceptual dimension in addition to lightness may contribute to the appearance of test patches in these displays. The present study explicitly tested whether two dimensions (lightness and transmittance) could lead to more satisfactory matches than lightness alone in an asymmetric matching task. We also examined whether transmittance matches were more strongly associated with task instructions that had observers match perceived transparency or the perceived edge contrast of the target relative to the surround. We found that matching target lightness in a homogeneous display to that in a textured or rocky display required varying both lightness and transmittance of the test patch on the textured display to obtain the most satisfactory matches. However, observers primarily varied transmittance when instructed to match the perceived contrast of targets against homogeneous surrounds, but not when instructed to match the amount of transparency perceived in the displays. The results suggest that perceived target-surround edge contrast differs between homogeneous and textured displays. Varying the midlevel property of transparency in textured displays provides a natural means for equating both target lightness and the unique appearance of the edge contrast in homogeneous displays.

Performance of advanced color difference and CAM02‐based formulas in prediction of the Crispening effect for reflective samples

AbstractThe Crispening effect is defined as an increase in the perceived color difference of the two stimuli, when their color (chromaticity or luminance) is close to the background on which the two stimuli are compared. In this study, the amount of the Crispening effect for three achromatic backgrounds and also the performance of six different color difference formulas (CDFs) for prediction of this effect have been investigated, by preparing 85 sample pairs in 9 CIE's recommended color centers. Regarding the results, the maximum (50%) and the minimum (4%) amount of the Crispening effect belong to the gray and the purple centers, respectively. According to the results of a comparative test, the Crispening intensifies when two stimuli have just lightness difference instead of just chromaticity difference. The highest variation was for the gray samples, in which the amount of the Crispening effect increased from 35% to 65%. By using PF/3 and STRESS index, it is also concluded that CMC and CIEDE2000 perform better than CAM02‐SCD and CAM02‐UCS in prediction of the Crispening effect on the dark gray and gray backgrounds. According to the results, the significant differences between the performances of the CDFs disappear when the luminance of the background increases. Huang's power functions also do not improve these results significantly. Furthermore, the results indicate that the traditional L* equation used in CIELAB performs similar to the Whittle's formula in prediction of the Crispening effect for reflective samples, and no significant difference was obtained.

The influence of lightness, and the crispening effect on the perceived contrast of textured images

We investigate the role of lightness perception in determining the perceived contrast of images. In particular, it is known that the background luminance of a display affects the relationship between onscreen luminance and perceived lightness. Stevens & Stevens (1963) modeled this effect using a simple power law. However, Whittle (1992) observed a more local effect, whereby subjects are more sensitive to lightness variations around the background luminance (the crispening effect). We probe lightness perception by asking subjects to manipulate the contrast of small patches on a uniform background until they appear to vary, from black to white, in a perceptually linear manner. In a second experiment, we estimate the contrast required to match the contrast of a light patch to that of a dark patch. Both experiments are conducted using five background luminance conditions, from 0 to 100% luminance. We find that subjects contrast judgments can only be modeled by first estimating the perceived lightness in a scene, using the empirically estimated lightness functions, before computing contrast. We conclude that models of contrast perception must include sophisticated models of lightness perception.

Evaluation of small suprathreshold color differences under different background colors

A psychophysical experiment under constant stimuli is conducted on a CRT display to measure the visual suprathreshold color differences for five color centers recommended by CIE under the same five background colors. The performances of four CIELAB-based, three CIECAM02-based, and two OSA-UCS-based formulas are tested. Detailed analysis results indicate the existence of chromatic crispening effect. CIEDE2000 performs best for the gray center and gray background, whereas CAM02-LCD and CAM02-UCS have the best performance for non-neutral backgrounds. CAM02-LCD significantly outperforms all other formulas for all color centers under all background colors.

Modeling lightness perception—another point of view

In a recent note, Brill and Carter propose to revisit the centuries‐old disagreement over the relationship between stimuli and perceived lightness or brightness and the mathematical model that best represents it. Here, the answer is offered that the only way to resolve this matter is empirically, with controlled experiments of different kinds that establish statistically meaningful and replicated data for a given set of test conditions and methodology. Given the fact that surround lightness has a very significant effect on the results, including the crispening effect, a model can only be valid for a limited set of conditions, and the likely outcome is multiple models or models with multiple variables. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 102–104, 2014

Basic Characteristics of Simultaneous Color Contrast Revisited

In this article, we present evidence supporting the hypothesis that the local mechanism of simultaneous color contrast is the same as the mechanism responsible for the crispening effect and the gamut expansion effect. A theoretically important corollary of this hypothesis is that the basic characteristics of simultaneous contrast are at odds with traditional laws. First, this hypothesis implies that the direction of the simultaneous contrast effect in color space is given by the vector from surround to target and not—as traditionally assumed—by the hue complementary to that of the surround. Second, it implies that the size of the simultaneous contrast effect depends on the difference between the target and surround colors in a way that challenges Kirschmann’s fourth law. The widespread belief in the traditional laws, we argue, is due to the confounding influence of temporal adaptation.

A simple model describes large individual differences in simultaneous colour contrast

We report experimental evidence for substantial individual differences in the susceptibility to simultaneous colour contrast. Interestingly, we found that not only the general amount of colour induction varies across observers, but also the general shape of the curves describing asymmetric matching data. A simple model based on von Kries adaptation and crispening describes the data rather well when we regard its free parameters as observer specific. We argue that the von Kries component reflects the action of a temporal adaptation mechanism, while the crispening component describes the action of the instantaneous, purely spatial mechanism most appropriately labeled simultaneous colour contrast. An interesting consequence of this view is that traditional ideas about the general characteristics of simultaneous contrast must be considered as misleading. According to Kirschmann’s 4th law, for instance, the simultaneous contrast effect should increase with increasing saturation of the surround, but crispening predicts the converse. Based on this reasoning, we offer a plausible explanation for the mixed evidence on the validity of Kirschmann’s 4th law. We also argue that simultaneous contrast, the crispening effect, Meyer’s effect and the gamut expansion effect are just different names for the same basic phenomenon.

Investigations of suprathreshold color-difference tolerances with different visual scales and different perceptual correlates using CRT colors

In order to investigate the performance of suprathreshold color-difference tolerances with different visual scales and different perceptual correlates, a psychophysical experiment was carried out by the method of constant stimuli using CRT colors. Five hue circles at three lightness (L*=30, 50, and 70) and chroma (C*ab=10, 20, and 30) levels were selected to ensure that the color-difference tolerances did not exceed the color gamut of the CRT display. Twelve color centers distributed evenly every 30 degrees along each hue circle were assessed by a panel of eight observers, and the corresponding color-difference tolerances were obtained. The hue circle with L*=50 and C*ab=20 was assessed with three different visual scales (DeltaV=3.06, 5.92, and 8.87 CIELAB units), which ranged from small to large visual scales, while the remaining hue circles were observed only with the small visual scale. The lightness tolerances had no significant correlation with the hue angles, while chroma and hue tolerances showed considerable hue angle dependences. The color-difference tolerances were linearly proportional to the visual scales but with different slopes. The lightness tolerances with different lightness levels but the same chroma showed the crispening effect to some extent, while the chroma and hue tolerances decreased with the increment of the lightness. For the color-difference tolerances with different chroma levels but the same lightness, there was no correlation between the lightness tolerances and the chroma levels, while the chroma and hue tolerances were nearly linearly proportional to the chroma levels.

Distinct Mechanisms Mediate Visual Detection and Identification

A core organizing principle for studies of the brain is that distinct neural pathways mediate distinct behavioral tasks [1, 2]. When two related tasks are mediated by a common pathway, studies of one are likely to generalize to the other. Here, we test whether performance on two laboratory tasks that model object detection and identification are mediated by common mechanisms of visual adaptation. Although both tasks rely on the luminance pattern in images, their demands on visual processing are quite different. Object detection requires discriminating image luminance differences associated with the light reflected from adjacent objects. To encode these differences reliably, neurons adapt their limited dynamic range to prevailing viewing conditions [3-6]. Object identification, on the other hand, demands a fixed response to light reflected from an object independent of illumination [7]. We compared performance in discrimination and identification tasks for simulated surfaces. In striking contrast to studies with less structured contexts, we found clear evidence that distinct processes mediate judgments in the two tasks. These results challenge models that account for perceived lightness entirely through the action of image-encoding mechanisms.

Background-Adjusted Weber-Fechner Fraction Considering Crispening Effect

The recognition limit of luminance difference in the human visual system (HVS) has not been studied systematically. In this paper, surround adapted Weber-Fechner fraction is calculated based on the crispening effect. It is found that surround adapted fractions have reduced to 1/3 of the traditional Weber-Fechner fractions. As compared with Breitmeyer's experiments, the presented result is a reasonable one. It can be used as some guide to design the digital display system when a designer needs to decide bit count of digital signal in considering of the limit of brightness level, and as the inspection tool of display manufacturing of brightness smear, defect, and so on.

Evaluation of the crispening effect using CRT‐displayed colour samples

AbstractIn this study, the crispening effect was clearly observed when 38 neutral‐coloured sample pairs with only lightness differences were assessed under 5 neutral backgrounds of different lightness values. The sample pairs are CRT‐based colours, and they are selected along the CIELAB L* axis from 0 to 100. The magnitude of colour difference of each pair is 5.0 CIELAB units. The visual assessment results showed that there is a very large crispening effect. The colour differences of the same pair assessed under different backgrounds could differ by a factor of up to 8 for a sample pair with low lightness. The perceived colour difference was enlarged when the lightness of a sample pair was similar to that of the background. The extent of crispening effect and its quantification are discussed in this investigation. The performances of five colour‐difference equations were also tested, including the newly developed CIEDE2000. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 374–380, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20045

Investigation of parametric effects using medium colour‐difference pairs

AbstractThe article investigates five types of parametric effects in assessing colour difference. The visual assessment experiments were conducted in six phases. The viewing parameters studied include the sample separation, sample size, and the background colours. The dataset prepared in this study includes a total of 107 cotton‐dyed pairs belonging to five colour centers. The average colour difference of the sample pairs was about 5.0 CIELAB units. Gray‐scale method was used for colour‐difference assessment with a panel of 10 observers (2 assessments each). The CIELAB colour‐difference formula was found to have the best performance over other formulae using the current dataset. In general, the parametric effects vary from 8–15%. When further analyzing the colour centers, it was found that much larger parametric effects of 42% and 26% were associated, respectively, with green sample pairs assessed on the green background and blue samples pairs assessed on the blue background. The green and blue background colours in these two cases are very close to the green and blue colour centers selected, which clearly indicates the crispening effect. © 2001 John Wiley & Sons, Inc. Col Res Appl, 26, 376–383, 2001

From color‐matching error to large color differences

AbstractClassical color‐matching error data have been compared in L, M, S cone response space to small and large color‐difference data to reveal their agreements and divergences. The color‐matching error data analyzed (with exception of the Brown data) and, implicitly, the Boynton–Kambe data were found to be similar, with a large ratio of S increment to L increment. Another group is formed by the Richter threshold data, small color‐difference data and the CIE94 formula fitted to the latter. This group has an S/L increment ratio of approximately one third that of the first. The Optical Society of America Uniform Color Scales and the Munsell set are on average comparable and intermediate in S/L increment ratio. Color‐matching error data, threshold and small color‐difference data as well as the formula fitted to it reveal a characteristic V shape of the cone response increment functions. It is explained as the overlay of a crispening effect onto the basic global increment function revealed in Munsell or OSA‐UCS data. © 2001 John Wiley & Sons, Inc. Col Res Appl, 26, 384–393, 2001

Grey scale, the “crispening effect”, and perceptual linearization

One way of optimizing a display is to maximize the number of distinguishable grey levels, which in turn is equivalent to perceptually linearizing the display. Perceptual linearization implies that equal steps in grey value evoke equal steps in brightness sensation. The key to perceptual linearization is hence to understand the relationship between screen luminance (differences) and perceived brightness (differences). We start with an overview of psychophysical laws on the brightness-luminance relationship. We present alternative models from the literature for describing this relationship. Existing models are compared with our human-performance data that were discussed in an earlier paper. We show that Whittle’s model provides a good fit to our experimental data, provided that some of the model parameters are allowed to depend on the surround luminance. An alternative model by Kingdom and Moulden, however, needs to be modified in order to accomplish agreement with experimental data.

Improved Discrimination near the Background Field: Transfer of the ‘Crispening Effect’ to Colour

Experiments are described which look for a ‘crispening effect’ in the hue domain. This effect—an enhanced discrimination around the adaptation level—has been shown for achromatic stimuli by both brightness scaling and contrast discrimination techniques (Whittle, 1992 Vision Research32 1493 – 1507). In the present experiments these techniques are applied to chromatic variations along L(-M)L-cone and S-cone axes (MacLeod — Boynton isoluminant chromaticity space). Results so far support a crispening effect for the L(-M)-cone axis but not the S-cone axis. This enhanced discriminatory power in the vicinity of the background luminance and hue accords with the importance of relative, rather than absolute, values for coding by the visual system.

Contrast-matching analysis of grating induction and suprathreshold contrast perception

The effect that induced gratings [Vision Res. 22, 119 (1982)] exert on the perceived contrast of standard gratings situated within a 0.5 degrees test field was assessed for two observers by a contrast-matching procedure. Five levels of inducing-grating contrast, CI, ranged from 0.0 to 0.75. Functions relating matching contrast, CM, to standard-grating contrast, CS, were obtained at four levels of inducing-grating contrast across a range of standard contrasts, -0.90 < or = CS < or = +0.90, where the sign denotes the spatial phase of the standard relative to the inducing grating. The matching functions possessed three distinct limbs separated by two inflection points; the limb between the inflection points represents a region of high contrast gain. Another measure, canceling contrast, was obtained at the four levels of inducing contrast by variation of CS until the test field appeared spatially homogeneous. Induction magnitude measured in terms of canceling contrast, CC, grew approximately linearly with CI, such that CC = 0.819 (CI). Induction magnitude determined from matching-contrast data obtained for homogeneous test fields (i.e., CM for CS = 0.0) grew as a decelerating function of inducing-grating contrast, such that CM = 0.308(CI]1.8 + 0.096), effectively asymptoting at a contrast of approximately 0.275 for CI > or = 0.50. When the difference between the absolute values of matching and standard contrast, magnitude of CM-magnitude of CS, is plotted against the ratio of standard to inducing-grating contrast, CS/CI, the resulting functions are generally biphasic, revealing regions of both contrast overmatching (i.e., magnitude of CM > magnitude of CS) and contrast undermatching, magnitude of CM < magnitude of CS. A four parameter model is presented that accounts for many features of the raw matching functions and that is mathematically similar to Semmelroth's account of the crispening effect in brightness matching [J. Opt. Soc. Am. 60, 1685 (1970)]. The model describes matching contrast, CM, as the weighted sum of two nonlinear contrast-response functions whose inputs are CS and CS-CI. The results are discussed relative to the crispening effect (the effect of contrast adaptation on perceived contrast) and to similarities and differences in luminance and contrast-domain visual processing.

Brightness, discriminability and the “Crispening Effect”

Subjects adjusted the luminances, L, of 16 or 25 circles, all visible at the same time on a computer monitor, to make equal-interval brightness series. The background was black, white or grey. The luminance steps between adjacent circles behaved like the luminance discrimination thresholds of Whittle, P. [(1986) Vision Research, 26, 1677–1691)]. They showed a sharp minimum at the background luminance, L b: the “Crispening Effect”. They followed Weber's Law with respect to L when L was small, but with respect to ΔL( = ¦ L − L b¦) near L b. The Crispening Effect was abolished by a thin outline or a hue difference between circles and background.

Filter model for lightness and brightness on different backgrounds.

A filter model is proposed to account for the effects of background luminance on perceived brightness or lightness of a target area. Special attention is focused on a crispening effect describable as a local increase of the rate of change of brightness with target luminance, as target luminance passes through the level of background luminance. The model is based on the assumption of competition, in the form of mutual-shunting-feedback inhibition, between target and surround.