Hue Shift Research Articles

Perceived shifts in saturation and hue of chromatic stimuli in the near peripheral retina

Using an asymmetric color matching technique, we measured the perceived changes that occur in the saturation and hue of colored stimuli at different eccentricities within the central 25 degrees of the human retina in nine color-normal subjects. A cone-opponent-based vector model was used to compute the activity of the L-M and S-(L+M) channels. The results show that a large proportion of the shifts in saturation and hue that occur with increasing retinal eccentricity are mirrored by decreased activity of the L-M channel. In comparison, the contribution of the S cone-opponent system undergoes relatively little change within the central 20 degrees . In addition, we also found that changes in saturation and hue are different from each other in terms of their variation across color space and their variation with stimulus size. Our findings suggest that perceived shifts in saturation and hue are mediated largely via the reduction in activation of the L-M cone-opponent channel but that saturation and hue might be subject to different retinal and/or cortical influences that contribute to their differing size dependencies in the peripheral retina.

Colour evaluation of freeze-dried roselle extract as a natural food colorant in a model system of a drink

The roselle extract, using acidified water–95% ethanol (1:1) as a solvent, was subjected to freeze-drying. Maltodextrin and trehalose, 2 and 3 g/100 ml extract, were used as stabilisers. Addition of the stabiliser retarded anthocyanin degradation. Colour changes of the freeze-dried roselle powder during storage were monitored using the CIELAB system. It was found that pigment concentration markedly changed with a minor change in lightness and hue. However, the changes in chroma mainly came from anthocyanin degradation. The freeze-dried roselle powder with maltodextrin (3 g/100 ml) proved to have superior colour stability. A model system of a drink adding this powder was carried out and the colour evaluation was compared to drinks containing commercial colorants: SAN RED RC ® and carmoesin. During a 12-week storage period at 30 °C, the change in hue of all three groups was within the same shade suggesting any change in pigment concentration had insignificant effect on hue shift. By contrast, the degradation of pigments highly correlated to changes in lightness and chroma. Even though a drink with roselle anthocyanin powder was the least stable in colour, the overall appearance of the drink was rated close to ‘like slightly’ throughout 56 days.

Color memory match under disparate viewing conditions

A color memory experiment with 5 colors (red, green, blue, yellow, and Caucasian skin color) was carried out. The color patches, shown on an LCD monitor, was memorized under a given viewing condition. The mixing of the memory color was then done first under the same viewing condition, and subsequently under other two altered viewing conditions. The conditions were different in the background and surround parameters. The color appearance model CIECAM02 was then used to predict color attributes under the altered viewing conditions. The lowest color memory shift in hue attribute was found for the red color. CIECAM02 seemed to have some limitation in colorfulness and chroma attribute prediction, for colors viewed on a black background. The result show, that the color attributes prediction in color memory experiment was not successful.

Effect of purity on hue (Abney effect) in various conditions

AbstractThe effect of purity on hue has been reported severally (including Munsell and NCS data on constant hue loci) over 100 years but without general agreement. For example, the number of hue shift nulls in the data vary from 2 to 6. Hence, despite this effect's commonality it lacks reliable data for modeling underlying mechanisms or color appearance. The purity of a stimulus may be decreased by adding white (as in Abney's experiment), by adding black, or by adding gray such that luminance, or alternatively lightness, remains constant. This article gives new data for CRT stimuli for illuminant D65 for all four conditions but mainly for equal luminance, for 31 observers and 13 test dominant wavelengths. Further, samples were observed in two temporal conditions: either simultaneously as pairs (the contrast mode) or singly (the no‐contrast mode). Three types of samples were tested: (1) equal luminance 30 cd/m2 for all dominant wavelengths, (2) equal lightness for all dominant wavelengths, and (3) zero‐gray colors, requiring different luminances for different dominant wavelengths. In all the above conditions, the resultant hue shifts graphed a robust bimodal curve (two peaks in cyan and red, two troughs in blue and green) across the hue cycle, similar to Munsell and NCS data except the definite peak in cyan.© 2006 Wiley Periodicals, Inc. Col Res Appl, 32, 25–39, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20286

Variant and invariant color perception in the near peripheral retina

Perceived shifts in hue that occur with increasing retinal eccentricity were measured by using an asymmetric color matching paradigm for a range of chromatic stimuli. Across nine observers a consistent pattern of hue shift was found; certain hues underwent large perceived shifts in appearance with increasing eccentricity, while for others little or no perceived shift was measured. In separate color naming experiments, red, blue, and yellow unique hues were found to be correlated with those hues that exhibited little or no perceptual shift with retinal eccentricity. Unique green, however, did not exhibit such a strong correlation. Hues that exhibited the largest perceptual shifts in the peripheral retina were found to correlate with intermediate hues that were equally likely to be identified by adjacent color naming mechanisms. However, once again the correlation was found to be weakest for the green mechanism. These data raise the possibility that perceptually unique hues are linked to color signals that represent the most reliable (minimally variant) chromatic information coming from the retina.

Spatial Dependence of Color Assimilation by the Watercolor Effect

Color assimilation with bichromatic contours was quantified for spatial extents ranging from von Bezold-type color assimilation to the watercolor effect. The magnitude and direction of assimilative hue change was measured as a function of the width of a rectangular stimulus. Assimilation was quantified by hue cancellation. Large hue shifts were required to null the color of stimuli < or = 9.3 min of arc in width, with an exponential decrease for stimuli increasing up to 7.4 deg. When stimuli were viewed through an achromatizing lens, the magnitude of the assimilation effect was reduced for narrow stimuli, but not for wide ones. These results demonstrate that chromatic aberration may account, in part, for color assimilation over small, but not large, surface areas.

Pigment Selection for an Inkjet Ink Set with Balanced Lightfade Performance

Careful pigment selection for an inkjet printer can achieve balanced lightfade performance. When a print fades from light exposure, commonly each colorant fades at a different rate. This results in an unwanted hue shift in addition to the overall loss in density. In a balanced system, each colorant fades at approximately the same rate. As a result, the amount of hue shift is reduced. The faded print is perceived as less objectionable to the user when the original hues are maintained. In order to create a balanced system, samples are printed with pigment and pigment blend candidates on a variety of media types. Those samples are exposed in a lightfade chamber, and density changes are measured over time. This data is used to select candidates with similar lightfade performance for each colorant of the system. Instead of attempting to maximize the lightfade performance of each colorant, other desirable performance attributes can be considered, such as chroma and cost. The achievement of a balanced lightfade system results in a more complete solution to the customer.

Bezold-Brucke hue shifts derived from hue-naming functions

Bezold-Brucke hue shifts derived from hue-naming functions

Bezold–Brücke effect in normal trichromats and protanopes

Luminance-dependent change in color appearance--the Bezold-Brücke effect--was investigated in protanopes and related to that in normal trichromats. Spectral lights were presented at six luminance levels covering mesopic, low, and high photopic vision-across three log steps from 0.76 to 760 Td. To judge color appearance, a variant of the color-naming method was used with four primary basic color terms and a "White" response. This modification enabled us to examine apparent saturation changes along with the Bezold-Brücke hue shift. Color-naming frequency functions were acquired across ten presentations of each stimulus. Since protanopes name colors idiosyncratically, changes in color appearance cannot be quantified directly from the color-naming functions. To circumvent the difficulty, these functions were transformed into color similarity measures for analysis with multidimensional scaling purported to reconstruct individual color spaces. In these, luminance-dependent shifts in color appearance were represented by means of geometric displacements. We found that for normal trichromats, shifts measured in this way agreed with those derived in our study directly, and with the hue shifts reported in earlier studies. For protanopes, contrary to some models of dichromatic vision, changes in color appearance are significant and indicate superimposed shifts in hue and saturation. The results obtained for normal trichromats, especially for protanopes, imply that nonlinearity in the yellow-blue opponent system is insufficient to explain the Bezold-Brücke effect, given the nature of the saturation shift and the demonstrated divergence between unique hues and invariant hues.

An evaluation of thermochromic prints based on microencapsulated liquid crystals using variable temperature colour measurement

A variable temperature colour measurement technique has been developed to characterise the temperature-dependent colour change, known as ‘colour play’, observed with thermochromic prints based on microencapsulated liquid crystals. The effect is most pronounced over a black background. The liquid crystals exhibiting the thermochromic effect adopt a chiral nematic phase with an underlying smectic A phase. A variety of methods for presenting and interpreting the data obtained, as the colour of the print passes through the spectrum, is explored. The effect of temperature on the wavelength of reflected light, a*b<ast; values, lightness, chroma and hue angle have been studied. The ‘blue phase’, exhibited transiently as the liquid crystal passes out of the chiral nematic phase to form an isotropic liquid, has been detected as an increase in lightness and a hue shift. Prints on nylon/lycra are found to have acceptable wash fastness, but show some sensitivity to light.

Revised Kubelka–Munk theory II Unified framework for homogeneous and inhomogeneous optical media

We extend the applicability of the recently revised Kubelka-Munk (K-M) theory to inhomogeneous optical media by treating inhomogeneous ink penetration of the substrate. We propose a method for describing light propagation in either homogeneous or inhomogeneous layers using series representations for the K-M scattering and absorption coefficients as well as for intensities of the upward and downward light streams. The conventional and matrix expressions for spectral reflectance and transmittance values of optically homogeneous media in the K-M theory are shown to be special cases of the present framework. Three types of ink distribution-homogeneous, linear, and exponential-have been studied. Simulations of spectral reflectance predict a depression of reflectance peaks and reduction of absorption bands characteristic of hue shifts and significant reduction of saturation and, in turn, color gamut.

A Color Appearance Model Applicable in Mesopic Vision

We propose a color vision model that can be used to predict color appearance in mesopic vision as well as photopic and scotopic vision. It is based on a two-stage model which consists of the cone and opponent stages and it assumes rod intrusion at the opponent stage. The model has the following features to describe the color appearance in mesopic vision. First, it includes a gradual and nonlinear shift in spectral luminous efficiency from V (λLD) to V′ (λLD) to cope with the spectral sensitivity difference between photopic and scotopic vision and the nonlinearity of rod influence on the luminance channel. Second, the model assumes decrease of the chromatic component with decreasing illuminance to explain the reduction of saturation at low illuminance levels. Third, it assumes that red/green and yellow/blue components change with illuminance levels independently, thus explaining hue shifts with decreasing illuminance. We applied the model for color appearance simulation of natural scenes in a mesopic visual environment.

Luminance-dependent hue shift in protanopes

For normal trichromats, the hue of a light can change as its luminance varies. This Bezold-Brücke (B-B) hue shift is commonly attributed to nonlinearity in the blue-yellow opponent system. In the present study, we questioned whether protanopes experience analogous changes. Two protanopes (Ps) viewed spectral lights at six luminance levels across three log steps. Two normal trichromats (NTs) were tested for comparison. A variant of the color-naming method was used, with an additional "white" term. To overcome the difficulty of Ps' idiosyncratic color naming, we converted color-naming functions into individual color spaces, by way of interstimulus similarities and multidimensional scaling (MDS). The color spaces describe each stimulus in terms of spatial coordinates, so that hue shifts are measured geometrically, as displacements along specific dimensions. For the NTs, a B-B shift derived through MDS agreed well with values obtained directly by matching color-naming functions. A change in color appearance was also observed for the Ps, distinct from that in perceived brightness. This change was about twice as large as the B-B shift for NTs and combined what the latter would distinguish as hue and saturation shifts. The protanopic analogue of the B-B shift indicates that the blue-yellow nonlinearity persists in the absence of a red-green signal. In addition, at mesopic levels (< or = 38 td), the Ps' MDS solution was two dimensional at longer wavelengths, suggesting rod input. Conversely, at higher luminance levels (76 td-760 td) the MDS solution was essentially one dimensional, placing a lower limit on S-cone input at longer wavelengths.

Chromatic and contrast selectivity in color contrast adaptation

We used color contrast adaptation to examine the chromatic and contrast selectivity of central color mechanisms. Adaptation to a field whose color varies along a single axis of color space induces a selective loss in sensitivity to the adapting axis. The resulting changes in color appearance are consistent with mechanisms formed by different linear combinations of the cone signals. We asked whether the visual system could also adjust to higher-order variations in the adapting stimulus, by adapting observers to interleaved variations along both the L versus M and the S versus LM cardinal axes. The perceived hue of test stimuli was then measured with an asymmetric matching task. Frequency analysis of the hue shifts revealed weak but systematic hue rotations away from each cardinal axis and toward the diagonal intermediate axes. Such shifts could arise if the adapted channels include mechanisms with narrow chromatic selectivity, as some physiological recordings suggest, but could also reflect how adaptation alters the contrast response function. In either case they imply the presence of more than two mechanisms within the chromatic plane. In a second set of measurements, we adapted to either the L versus M or the S versus LM axis alone and tested whether the changes in hue could be accounted for by changes in relative contrast along the two axes. For high contrasts the hue biases are larger than the contrast changes predict. This dissociation implies that the contrast and hue changes are not carried by a common underlying signal, and could arise if the contrast along a single color direction is encoded by more than one mechanism with different contrast sensitivities or if different subsets of channels encode contrast and hue. Such variations in contrast sensitivity are also consistent with physiological recordings of cortical neurons.

A new look at the Bezold–Brücke hue shift in the peripheral retina

Experiments were conducted with a bipartite field to better understand the Bezold–Brücke hue shift in the peripheral retina. The first experiment measured hue shift in the fovea and at 1° and 8° along the horizontal meridian of the nasal retina for nominal test wavelengths of 430, 450, 490, 520 and 610 nm. Peripheral measurements were obtained under two adaptation conditions: after 30 min dark adaptation and following a rod-bleach. Results indicated that foveal hue shifts differed from those obtained after a rod-bleach. Data from the rod-bleach and no-bleach conditions in the periphery were similar, indicating that rods could not account for the differences between the foveal data and the rod-bleach peripheral data. Hue shifts obtained for the 520 nm test stimulus, and to a smaller extent other test wavelengths, at 8° nasal retinal eccentricity revealed that the wavelength of the matching stimulus depended upon the lateral position of the matching and test fields, and this effect was greater in the no-bleach condition than the rod-bleach condition. Several factors were investigated in experiments 2 and 3 to explain the results with the 520 nm test field. It appears that differential rod density under the two half fields and the compression of photoreceptors by the optic disk may partially, but not fully, account for the 520 nm effect.

Evidence for Thermally Induced Fade and Yellow Stain Formation in Inkjet Photographic Prints

In our previous papers, we have shown how light, ozone, and humidity can affect the image stability of inkjet photographic prints. Previous attempts to measure the thermal dark fade of inkjet prints by the Arrhenius method have been confounded by dye migration. When tests are carried out at a constant, absolute humidity equivalent to 50% RH at 24&#xB0;C (constant 13&#xB0;C dew point), temperatures as high as 75&#xB0;C can be utilized for many ink-media combinations without encountering significant dye migration. In this paper, we provide evidence for thermally induced changes to inkjet photographic prints, including fade, hue shift, and/or yellowing. Results will be discussed in the context of the Arrhenius relationship.

Hypotheses for chromatic opponency functions and their performance on classical psychophysical data

General hypothesis for the definition of chromatic-opponency functions are given in a black-box approach to the problem. It is supposed that the color signals in the visual color processing can be factorized into the product of the lightness times a pair of chromatic opponency functions and the whole chromatic processing consists of three independent processes: a linear transformation, a logarithmic compression, and a chromatic opponency actuation. The main chromatic opponency functions, obtainable by very general hypothesis on the symmetry and on the homogeneity degree, are supposed equal to the logarithms of tristimulus-value ratios in a proper reference frame of the tristimulus space. The perceptual chromatic functions, individually with uniform scales, are a linear mixing of the main chromatic opponency functions. The Bezold–Brücke hue shift is not considered. A performance of these hypothesis is successfully realized on the OSA-UCS system, for extra macula vision, and on the chromatic discrimination ellipses, for macular vision. Unique hues are derived from the main chromatic opponency functions of spectral lights. © 2004 Wiley Periodicals, Inc. Col Res Appl, 30, 31–41, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20072

Color appearance in the entire visual field: color zone map based on the unique hue component.

To provide the fundamental data for a color zone map, the color appearances of nearly unique hue stimuli presented over the entire visual field were qualitatively and quantitatively evaluated by hue and saturation judgments, blackness evaluation, and categorical color naming. The hue of red and green stimuli shifts toward a unique yellow, while that of yellow and blue does not change with an increase in eccentricity. The saturation of all the stimuli falls with an increase in the eccentricity in all directions. On the basis of the unique hue component, color zone maps for red, dark yellow, yellow, green, and blue stimuli are drawn. All the color zone maps extend over a wider region in the temporal and lower directions than in the nasal and upper directions of the visual field. The results are compared with the color zones of previous studies. The relationship between the color zones and the color categorization, as well as the underlying mechanisms of reduced saturation and hue shift, is discussed.

Moving objects appear to slow down at low contrasts

Moving cars give the illusion of slowing down in foggy conditions, because low contrast reduces perceived speed. A grey square that drifts horizontally across a surround of black and white vertical stripes appears to stop and start as it crosses each stripe, because its contrast keeps changing. A moving square whose vertical and horizontal edges have different contrasts will show illusory distortions in perceived direction. Contrast also affects the apparent amplitude and salience of back-and-forth apparent motion. Finally, a line of black and white dots on a grey surround moves in illusory directions, because of a mismatch in the contrasts along and across the dotted line. Thus, motion signals in the early parts of the visual system are profoundly altered by stimulus luminance and contrast. This suggests that motion is coded by the relative firing rates of neural channels tuned to fast and slow motion, with contrast-dependence being a motion analog of the Bezold–Brucke hue shift.

Remote adaptation effect on perceived subjective color: A model approach

AbstractAn elaborated subjective color model is presented that includes the predictions of emulated Benham disk results and additional predictions that refer to local and remote achromatic illuminations on perceived subjective color shifts. A computer emulated Benham disk pattern was used as a stimulus to test the effects of remote illumination on its color sensation. An analytical model and its predictions are proposed in order to account for the results of the perceived hue shift, when changing either the remote illumination area or the stimulus illumination. This model is based on previous retinal color‐coded cells responses which yield the subjective color, and on local and remote adaptation mechanisms. The similarity between the role and mechanism of remote illumination (achromatic or chromatic) in subjective and perceived color is also discussed. © 2003 Wiley Periodicals, Inc. Col Res Appl, 28, 197–208, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10145