Color contrast and contextual influences on color appearance

Mizokami

Network: Computation in Neural Systems

2007

Self Cite

We examined how the distribution of colors in natural images varies as the seasons change. Images of natural outdoor scenes were acquired at locations in the Western Ghats, India, during monsoon and winter seasons and in the Sierra Nevada, USA, from spring to fall. The images were recorded with an RGB digital camera calibrated to yield estimates of the L, M, and S cone excitations and chromatic and luminance contrasts at each pixel. These were compared across time and location and were analyzed separately for regions of earth and sky. Seasonal climate changes alter both the average color in scenes and how the colors are distributed around the average. Arid periods are marked by a mean shift toward the +L pole of the L vs. M chromatic axis and a rotation in the color distributions away from the S vs. LM chromatic axis and toward an axis of bluish-yellowish variation, both primarily due to changes in vegetation. The form of the change was similar at the two locations suggesting that the color statistics of natural images undergo a characteristic pattern of temporal variation. We consider the implications of these changes for models of both visual sensitivity and color appearance.

Section: Methodsmentioning

confidence: 99%

Seasonal variations in the color statistics of natural images

Mizokami

Network: Computation in Neural Systems

2007

Self Cite

“…Thus both adaptation and induction adjust color appearance according to both the mean and variance of the surround (Brown & MacLeod, 1997, Singer & D'Zmura, 1994, Webster, Malkoc, Bilson & Webster, 2002). Both can also adjust to high-level perceptual attributes (Shevell, 2012, Shevell & Kingdom, 2008, Webster, 2011).…”

Section: From Temporal To Spatial Contextmentioning

confidence: 99%

Probing the functions of contextual modulation by adapting images rather than observers

2014

Vision Research

Self Cite

Countless visual aftereffects have illustrated how visual sensitivity and perception can be biased by adaptation to the recent temporal context. This contextual modulation has been proposed to serve a variety of functions, but the actual benefits of adaptation remain uncertain. We describe an approach we have recently developed for exploring these benefits by adapting images instead of observers, to simulate how images should appear under theoretically optimal states of adaptation. This allows the long-term consequences of adaptation to be evaluated in ways that are difficult to probe by adapting observers, and provides a common framework for understanding how visual coding changes when the environment or the observer changes, or for evaluating how the effects of temporal context depend on different models of visual coding or the adaptation processes. The approach is illustrated for the specific case of adaptation to color, for which the initial neural coding and adaptation processes are relatively well understood, but can in principle be applied to examine the consequences of adaptation for any stimulus dimension. A simple calibration that adjusts each neuron’s sensitivity according to the stimulus level it is exposed to is sufficient to normalize visual coding and generate a host of benefits, from increased efficiency to perceptual constancy to enhanced discrimination. This temporal normalization may also provide an important precursor for the effective operation of contextual mechanisms operating across space or feature dimensions. To the extent that the effects of adaptation can be predicted, images from new environments could be “pre-adapted” to match them to the observer, eliminating the need for observers to adapt.

“…A test light surrounded by a mosaic with a broad range of chromaticities compresses the perceived saturation of a chromatic light [16]. A mosaic with all of its various chromaticities restricted to any specific single direction in color space causes hue changes consistent with chromatically-selective sensitivity loss along the adapted direction, which suggests the color changes from a complex surround are mediated by a cortical neural process [17]. A central neural locus is corroborated by presenting a test field in one eye and then introducing chromatic variation within a nearby retinotopic area, in either the same eye or opposite eye; the chromatic variation in either eye causes the same shifts in the color appearance of the test [18].…”

Section: Mechanisms Mediating Color Appearancementioning

confidence: 99%

The Verriest Lecture: Color lessons from space, time and motion

Shevell¹

2012

J. Opt. Soc. Am. A

The appearance of a chromatic stimulus depends on more than the wavelengths composing it. The scientific literature has countless examples showing that spatial and temporal features of light influence the colors we see. Studying chromatic stimuli that vary over space, time or direction of motion has a further benefit beyond predicting color appearance: the unveiling of otherwise concealed neural processes of color vision. Spatial or temporal stimulus variation uncovers multiple mechanisms of brightness and color perception at distinct levels of the visual pathway. Spatial variation in chromaticity and luminance can change perceived three-dimensional shape, an example of chromatic signals that affect a percept other than color. Chromatic objects in motion expose the surprisingly weak link between the chromaticity of objects and their physical direction of motion, and the role of color in inducing an illusory motion direction. Space, time and motion – color’s colleagues – reveal the richness of chromatic neural processing.