Hue Shift Research Articles

Neurophysiological correlates of color vision: A model.

tree-receptor theory of human color vision accounts for color matching. A bottom-up, non-linear model combining cone signals in six types of cone-opponent cells in the lateral geniculate nucleus (LGN) of primates describes the phenomenological dimensions hue, color strength, and lightness/brightness. Hue shifts with light intensity (the Bezold-Brucke phenomenon), and saturation (the Abney effect) are also accounted for by the opponent model. At the threshold level, sensitivities of the more sensitive primate cells correspond well with human psychophysical thresholds. Conventional Fourier analysis serves well in dealing with the discrimination data, but here we want to take a look at non-linearity, i.e., the neural correlates to perception of color phenomena for small and large fields that span several decades of relative light intensity. We are particularly interested in the mathematical description of spectral opponency, receptive fields, the balance of excitation and inhibition when stimulus size changes, and retina-to-LGN thresholds. Keywords: human color vision, opponent theory, three-color theory, three-receptor theory, perception, neuroscience.

A Robust Hue Descriptor

A hue descriptor based on Logvinenko's illuminantinvariant object colour atlas [1] is tested in terms of how well it maps hues to the hue names found in Moroney's Colour Thesaurus [2] [3] and how well it maps hues of Munsell papers to their corresponding Munsell hue designator. Called the KSM hue descriptor, it correlates hue with the central wavelength of a Gaussian-shaped reflectance function. An important feature of this representation is that the set of hue descriptors inherits the illuminate invariant property of Logvinenko's object colour atlas. Despite the illuminant invariance of the atlas and the hue descriptors, metamer mismatching means that colour stimulus shift [4] can occur, which will inevitably lead to some hue shifts. However, tests show that KSM hue is robust in the sense that it is much more stable under a change of illuminant than CIELAB hue.

Species-Specific Relationships between Water Transparency and Male Coloration within and between Two Closely Related Lake Victoria Cichlid Species.

Environmental variation in signalling conditions affects animal communication traits, with possible consequences for sexual selection and reproductive isolation. Using spectrophotometry, we studied how male coloration within and between populations of two closely related Lake Victoria cichlid species (Pundamilia pundamilia and P. nyererei) covaries with water transparency. Focusing on coloration patches implicated in sexual selection, we predicted that in clear waters, with broad-spectrum light, (1) colours should become more saturated and (2) shift in hue away from the dominant ambient wavelengths, compared to more turbid waters. We found support for these predictions for the red and yellow coloration of P. nyererei but not the blue coloration of P. pundamilia. This may be explained by the species difference in depth distribution, which generates a steeper gradient in visual conditions for P. nyererei compared to P. pundamilia. Alternatively, the importance of male coloration in intraspecific sexual selection may differ between the species. We also found that anal fin spots, that is, the orange spots on male haplochromine anal fins that presumably mimic eggs, covaried with water transparency in a similar way for both species. This is in contrast to the other body regions studied and suggests that, while indeed functioning as signals, these spots may not play a role in species differentiation.

The relationship between peripherally matched invariant hues and unique hues: a cone-contrast approach

A characteristic shift in hue and saturation occurs when colored targets are viewed peripherally compared with centrally. Four hues, one in each of the red, blue, green, and yellow regions of color space, remain unchanged when presented in the peripheral field. Apart from green, these peripherally invariant hues correspond almost exactly in color space with the unique hues. We explore this puzzling observation using asymmetric color-matching and color-naming experiments and computing cone contrasts for peripheral and central stimuli. We find that the difference between cone contrasts for the peripheral and central stimuli reaches a maximum at the chromatic axis corresponding to peripherally invariant green. We speculate that the effect is linked to a weakened signal from M-cones and probably associated with a reduced number of M-cones in peripheral retina.

Real-world stimuli show perceived hue shifts in the peripheral visual field

Certain hues undergo shifts in their appearance when they are viewed by the peripheral retina. This has often been shown on a 3-primary color CRT monitor. To investigate the possible role of metamerism, we replicated our peripheral color matching experiments using Munsell paper stimuli viewed under real and simulated daylight (using a 3-primary projection system). Using stimuli of constant value and chroma (7/4), observers adjusted the hue of a 3 deg target presented 18 deg nasally, until it matched a 1 deg target presented 1 deg nasally. The magnitude and pattern of measured hue shifts were similar to those measured using CRT stimuli. We conclude that the perceived hue shifts that have previously been reported in the peripheral retina are independent of the nature of the stimulus and of the illuminant.

A Simple Algorithm for Managing Color in Global Tone Reproduction

Abstract Simple tone reproduction methods, such as the Reinhard global photographic tone-mapping operator, are popular methods for mapping high-dynamic range images to a low-dynamic range display. However, these methods deal mainly with how luminance is mapped; much less attention has been paid to how a full RGB color is produced. We introduce a simple method, inspired by traditional photography's use of polarizers to manage color, to map RGB colors when using global photographic operators for luminance. This method allows the user to trade off luminance for colorfulness, avoids unpredictable hue shifts and desaturation of the image, and guarantees that results lie in the RGB color cube without clamping.

Unique hue data for colour appearance models. Part II: Chromatic adaptation transform

AbstractUnique hue settings of 185 observers under three room‐lighting conditions were used to evaluate the accuracy of full and mixed chromatic adaptation transform models of CIECAM02 in terms of unique hue reproduction. Perceptual hue shifts in CIECAM02 were evaluated for both models with no clear difference using the current Commission Internationale de l'Éclairage (CIE) recommendation for mixed chromatic adaptation ratio. Using our large dataset of unique hue data as a benchmark, an optimised parameter is proposed for chromatic adaptation under mixed illumination conditions that produces more accurate results in unique hue reproduction. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2013

Color-accurate underwater imaging using perceptual adaptive illumination

Capturing color in water is challenging due to the heavy non-uniform attenuation of light in water across the visible spectrum, which results in dramatic hue shifts toward blue. Yet observing color in water is important for monitoring and surveillance as well as marine biology studies related to species identification, individual and group behavior, and ecosystem health and activity monitoring. Underwater robots are equipped with motor control for large scale transects but they lack sensors that enable capturing color-accurate underwater images. We present a method for color-accurate imaging in water called perceptual adaptive illumination. This method dynamically mixes the illumination of an object in a distance-dependent way using a controllable, multi-color light source. The color mix compensates correctly for color loss and results in an image whose color composition is equivalent to rendering the object in air. Experiments were conducted with a color palette in the pool and at three different coral reefs sites, and with an underwater robot collecting image data with the new sensor.

18.4: Color Perception in LED Projectors

AbstractAn evaluation model for the perceived brightness and the perceived hue shift both in LED projectors has been established. Two series of visual observation experiments are performed for studying the color perception. Finally, the predictability of the evaluation model is also verified in human visual comparison.

Paramer Mismatch-Based Spectral Gamut Mapping

A spectral agreement between the original scene and a printed reproduction is required to achieve an illuminant-invariant visual match. This is usually impossible since the spectral gamut of typical printing systems is only a small subset of all natural reflectances. Out-of gamut reflectances need to be mapped into the spectral gamut of the printer minimizing the perceived error between original and reproduction for more than one illuminant. In this paper, we propose an algorithmic framework for spectral gamut mapping to achieve a reproduction that is as visually correct as a colorimetric reproduction for one illuminant and is superior for a set of other illuminants. A sequence of hierarchical mappings in 3-D color spaces are performed utilizing the observer's color quantization to increase the spectral variability of subsequent transformations: For the most important illuminant a traditional colorimetric gamut mapping is performed. For any additional illuminants colors are mapped onto pixel-dependent paramer mismatch gamuts preserving the visual equivalence of previous transformations. We present a separation method for investigating the spectral gamut mapping framework and show that hue shifts and chroma gains cannot be always avoided for the second and subsequent illuminants and that the order of illuminants has a large impact on the final reproduction.

A behavioural investigation of human visual short term memory for colour

We examined visual short term memory (VSTM) for colour using a delayed-match-to-sample paradigm. In these experiments we measured the effects of increasing inter-stimulus interval (ISI), varying between 0 and 10 s, on the ability of five colour normal human observers to make colour matches between a reference and subsequently presented test stimuli. The coloured stimuli used were defined by different chromatic axes on the isoluminant plane of DKL colour space. In preliminary experiments we used a hue scaling procedure to identify a total of 12 colour stimuli which served as reference hues in the colour memory experiments: four stimuli were exemplars of red, green, blue and yellow colour appearance categories, four were located between these categories and a further four were located on the cardinal axes that isolated the activity of the cone-opponent mechanisms. Our results demonstrate that there is a reduction in the ability of observers to make accurate colour matches with increasing ISIs and that this reduced performance was similar for all colour stimuli. However, the shifts in hue that were measured between the reference and matched test stimuli were significantly greater for the cardinal stimuli compared to those measured for the stimuli defined by the hue scaling procedure. This deterioration in the retention of hue in VSTM for stimuli that isolate cone-opponent mechanisms may be a reflection of the reorganisation of colour processing that occurs in the cortex where colour appearance mechanisms become more prominent.

Colour appearance shifts in two different‐sized viewing conditions

AbstractThis study assessed the effect of size on colour appearance, using a colour matching paradigm where two sizes were presented in a setting similar to a normal colour selection interface. Twelve colours sampling the entire range of the colour spectrum were chosen as target stimuli. The target stimuli consisted of either a large (30° by 50°) or a small (0.5° by 0.5°) test field displayed on a cathode ray tube (CRT). In the experiment, a set of small colour samples consisting of the target and its neighboring colours was presented on the screen. Fifty‐seven participants were asked to pick a colour from the sample set that appeared to exactly match the target. Results in CIECAM02 showed a consistent increase in the apparent brightness (Q) but some decrease in saturation (s) for the larger field. Hue shifts were observed to form a systematic pattern. We noticed a discernable trend showing that, for targets of bluish or purplish colour hues, the accuracy of colour matching is lower and colour difference is greater in the condition of the large viewing field. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010

Isolation and antisense suppression of flavonoid 3', 5'-hydroxylase modifies flower pigments and colour in cyclamen.

BackgroundCyclamen is a popular and economically significant pot plant crop in several countries. Molecular breeding technologies provide opportunities to metabolically engineer the well-characterized flavonoid biosynthetic pathway for altered anthocyanin profile and hence the colour of the flower. Previously we reported on a genetic transformation system for cyclamen. Our aim in this study was to change pigment profiles and flower colours in cyclamen through the suppression of flavonoid 3', 5'-hydroxylase, an enzyme in the flavonoid pathway that plays a determining role in the colour of anthocyanin pigments.ResultsA full-length cDNA putatively identified as a F3'5'H (CpF3'5'H) was isolated from cyclamen flower tissue. Amino acid and phylogeny analyses indicated the CpF3'5'H encodes a F3'5'H enzyme. Two cultivars of minicyclamen were transformed via Agrobacterium tumefaciens with an antisense CpF3'5'H construct. Flowers of the transgenic lines showed modified colour and this correlated positively with the loss of endogenous F3'5'H transcript. Changes in observed colour were confirmed by colorimeter measurements, with an overall loss in intensity of colour (C) in the transgenic lines and a shift in hue from purple to red/pink in one cultivar. HPLC analysis showed that delphinidin-derived pigment levels were reduced in transgenic lines relative to control lines while the percentage of cyanidin-derived pigments increased. Total anthocyanin concentration was reduced up to 80% in some transgenic lines and a smaller increase in flavonol concentration was recorded. Differences were also seen in the ratio of flavonol types that accumulated.ConclusionTo our knowledge this is the first report of genetic modification of the anthocyanin pathway in the commercially important species cyclamen. The effects of suppressing a key enzyme, F3'5'H, were wide ranging, extending from anthocyanins to other branches of the flavonoid pathway. The results illustrate the complexity involved in modifying a biosynthetic pathway with multiple branch points to different end products and provides important information for future flower colour modification experiments in cyclamen.

On the spectral relation between the first and second Stiles–Crawford effect

The first Stiles–Crawford effect describes the psychophysical visibility dependence on pupil point for a narrow beam of light incident on the eye. Its distribution function commonly attributed to photoreceptor waveguiding is characterized by a point of maximum visibility typically near the pupil centre and a wavelength-dependent directionality parameter. The second Stiles–Crawford effect describes a minor hue shift of obliquely incident light commonly attributed to pigment screening that accompanies observations of the first Stiles–Crawford effect. Here the first Stiles–Crawford effect and the wavelength dependence of its directionality parameter are examined in terms of photoreceptor waveguiding. Its distribution function is analyzed to derive characteristic features of the second Stiles–Crawford effect directly from the spectrum of the directionality parameter. The results obtained are independent of the exact physical mechanisms underlying both effects but do support a major role played by waveguiding. Finally, the influence of bleaching is discussed in relation to the model and to pigment screening.

The watercolor effect: Spacing constraints

The watercolor effect (WCE) is a long-range color assimilation effect occurring within an area enclosed by a light chromatic contour, which in turn is surrounded by a dark chromatic contour. Here, we studied the effects of chromatic modulation of the WCE for different kinds of spacing between and within the inducing contours, using a hue-cancellation method. When an empty zone or interspace was inserted between the inducing contours (radial spacing), the hue shift required to null the induced coloration rapidly decreased with increasing spacing between the two contours. Similarly, when the continuous contours were replaced by dotted contours (lateral spacing), the shift in chromaticity quickly decreased with increasing distance between the dots. In this case, the decrease was similar for chains of paired dots (“in-phase”) and chains of unpaired dots (“out-of-phase”). Results demonstrate that the WCE is strongest when the two inducing contours are spatially contiguous and continuous. The neural implications of these findings are discussed.

Structural colours create a flashing cue for sexual recognition and male quality in a Neotropical giant damselfly

Summary1. Structural coloration is common among animals that produce sexual displays involving motion or ultraviolet reflection. Different sources of colour may provide multicomponent signals that indicate the location, sex, and fitness of a potential mate or rival. We investigated the proximate basis and ultimate function of the wing coloration of the territorial damselflyMegaloprepus caerulatus,which produces a dynamic, high contrast display during flight. The wings of both sexes have blue and white bands, but the location of the white patches are sex specific.2. Wax filaments produce diffuse, white areas through broadband scattering of wavelengths between 300 and 700 nm. Blue bands reflect wavelengths between 300 and 500 nm (λmax = 398 nm) and shift in hue with viewing angle, the result of thin layer interference produced by layers of cuticle and pigment within the wing membrane. Both wing bands strongly reflect UV wavelengths.3. Both the iridescent UV‐blue and white wing patches provide high contrast against the vegetation in forest light gaps where mating occurs. Moreover, the iridescent signal oscillates during flight. Angle‐dependent UV‐blue iridescence is periodically extinguished during each wing beat cycle, in contrast to the white areas, which remain bright.4. Males distinguish potential mates from rivals by the presence of a female’s white wing tip. Blackening the white wing bands of males and adding white wing tips to resemble a female elicits a sexual rather than aggressive response from males. Conversely, blackening the white wing tips of females reduces sexual responses.5. The proportional area of the white wing bands of males is indicative of wing symmetry, correlated with body size, and in turn, territory residency suggesting that it may serve as a signal of male condition during intra‐ and intersexual interactions.6. We propose that the flashing iridescent UV‐blue wing bands provide a beacon to potential mates across forest light gaps, whereas the white patches serve in mate recognition and may indicate male quality or territorial status. Our study identifies a unique combination of interference and broadband reflectors that provide a dynamic multicomponent signal.

Hue and saturation shifts from spatially induced blackness

We studied changes in the color appearance of a chromatic stimulus as it underwent simultaneous contrast with a more luminous surround. Three normal trichromats provided color-naming descriptions for a 10 cd/m2 monochromatic field while a broadband white annulus surround ranged in luminance from 0.2 cd/m2 to 200 cd/m2. Descriptions of the chromatic field included Red, Green, Blue, Yellow, White, and Black or their combinations. The naming frequencies for each color/surround were used to calculate measures of similarity among the stimuli. Multidimensional scaling analysis of these subjective similarities resulted in a four-dimensional color space with two chromatic axes, red-green and blue-yellow, and two achromatic axes, revealing separate qualities of blackness/lightness and saturation. Contrast-induced darkening of the chromatic field was found to be accompanied by shifts in both hue and saturation. Hue shifts were similar to the Bezold-Brücke shift; shifts in saturation were also quantified. A stage model is proposed to account for the relationships among blackness induction and the inherent nonlinearities in chromatic and achromatic processing.

Hue-Shift Modeling and Correction Method for High Luminance Display

The human eye usually experiences a loss of color sensitivity when it is subjected to high levels of luminance, and perceives a discrepancy in color between high and normal-luminance displays, generally known as a hue shift. Accordingly, this paper models the hue-shift phenomenon and proposes a hue correction method to provide perceptual matching between high and normal-luminance displays. The modeling of the hue-shift phenomenon is determined by perceived hue matching experiments. To quantify the hue-shift phenomenon for the whole hue angle, 24 color patches with the same lightness are first created and equally spaced inside the hue angle for three lightness levels. These patches are then displayed one-by-one on both displays with the ratio of luminance between the two displays. Next, the hue value for each patch appearing on the high luminance display is adjusted by observers until the perceived hue for the patches on both displays appears the same visually. After obtaining the hue-shift values from the perceived hue matching experiment, these values are fit piecewise into seven sinusoidal functions to allow the shifted-hue amounts to be approximately determined for arbitrary hue values of pixels in a high luminance display and then used for correction. Essentially, the input red green blue (RGB) values of an image are converted to CIELAB values by a forward characterization model, and then, LCh (lightness, chroma, and hue) values are calculated to obtain the hue values for all the pixels. These hue values are shifted according to the amount calculated by the functions of the hue-shift model. Finally, the corrected CIELAB values are calculated from lightness, chroma, and corrected hue values, and after that, the output RGB values for all pixels are estimated by an inverse characterization model. For evaluation, an observer's preference test was performed using several test images with other hue shift results and the comparison results are shown with a z score.

Characterisation and calibration of three physical forms of thermochromic liquid crystals

Liquid crystal thermography (LCT) provides a colour response proportional to the temperature of a heated surface in contact with the crystals. Thermochromic liquid crystals (TLC) are offered in the form of an emulsion, polymer sheet or latex support. Wider adoption of this technology has been limited due to response time, pressure sensitivity and imaging equipment. It is important to characterise TLC based on their chemical composition, colour play interval, spatial density and repeatability. This paper presents results for three forms of TLC material in terms of the effects of incident lighting, pressure sensitivity and hysteresis. Data are presented in the form of hue versus temperature calibration curves. Hue versus temperature curve shifts towards higher hue values for the identical temperature producing a maximum change of 15–20% in hue when the lighting intensity is changed from minimum to maximum. Hysteresis in the calibration curve occurred when the liquid crystals were heated above the colour play range producing a maximum temperature change of 1°C for R25C5W TLC sheet. This hysteresis was not permanent. The authors recommend using liquid crystals within their colour bandwidth to overcome hysteresis effects. The results may be helpful in developing LCT for various biomedical applications.

A Multiscale Framework for Spatial Gamut Mapping

Image reproduction devices, such as displays or printers, can reproduce only a limited set of colors, denoted the color gamut. The gamut depends on both theoretical and technical limitations. Reproduction device gamuts are significantly different from acquisition device gamuts. These facts raise the problem of reproducing similar color images across different devices. This is well known as the gamut mapping problem. Gamut mapping algorithms have been developed mainly using colorimetric pixel-wise principles, without considering the spatial properties of the image. The recently proposed multilevel gamut mapping approach takes spatial properties into account and has been demonstrated to outperform spatially invariant approaches. However, they have some important drawbacks. To analyze these drawbacks, we build a common framework that encompasses at least two important previous multilevel gamut mapping algorithms. Then, when the causes of the drawbacks are understood, we solve the typical problem of possible hue shifts. Next, we design appropriate operators and functions to strongly reduce both haloing and possible undesired over compression. We use challenging synthetic images, as well as real photographs, to practically show that the improvements give the expected results.