Frequency of metamerism in natural scenes (original) (raw)
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The Frequency of Metamerism in Natural Scenes
Estimates of the frequency of metameric surfaces, which appear the same to the eye under one illuminant but different under another, were obtained from 50 hyperspectral images of natural scenes. The degree of metamerism was specified with respect to a color-difference measure after allowing for full chromatic adaptation. The relative frequency of metameric pairs of surfaces, expressed as a proportion of all pairs of surfaces in a scene, was very low. Depending on the criterion degree of metamerism, it ranged from about 10 −6 to 10 −4 for the largest illuminant change tested, which was from a daylight of correlated color temperature 25,000 K to one of 4000 K. But, given pairs of surfaces that were indistinguishable under one of these illuminants, the conditional relative frequency of metamerism was much higher, from about 10 −2 to 10 −1 , sufficiently large to affect visual inferences about material identity.
Incidence of metamerism in natural scenes
Estimates of the incidence of metameric surfaces, defined as having different spectral reflectances but appearing the same under a given light, were obtained from 40 hyperspectral images of natural scenes. The degree of metamerism was specified with respect to a color-difference metric after allowing for full chromatic adaptation to the scene. Although the proportion of pairs of surfaces in an image that were metameric was very low, between about 10 −4 and 10 −5 , the relative proportion, i.e. of pairs indistinguishable under one of the daylights that were metameric was high, of the order of 10 −1 , depending on the type of scene and criterion degree of metamerism. The proportion of metamers in scenes containing foliage was generally higher than in scenes containing man-made structures, and this difference increased as the degree of metamerism increased.
Predicting frequency of metamerism in natural scenes by entropy of colors
Estimating the frequency of metameric surfaces in natural scenes usually requires many comparisons of surface colors to determine which are visually indistinguishable under one light but distinguishable—by a certain criterion degree—under another. The aim here was to test the predictive power of a simpler approach to estimation based on the entropy of colors. In simulations with 50 hyperspectral images of natural scenes, the logarithm of the observed relative frequency of metamerism in each scene under two successive daylights was regressed on combinations of the estimated Shannon differential entropies of the colors of the scene under the same two daylights. The regression was strong, and it remained so when restricted to the estimated differential entropy under just the first daylight, providing that the criterion degree of metamerism was limited. When the criterion degree was made more extreme, however, the restricted regression failed. A possible explanation of the predictive power of differential entropy is briefly considered.
Proc.Roy. Photo. Soc. Confrence " Digital Futures", 2000
The accuracy of image-capture is examined, in terms of reproduced colour co-ordinates. Variation in colorimetric accuracy, caused by detailed spectral variation in sensor response is discussed. The characteristics, both of human observers modelled by CIE Colorimetry, and of digital cameras are analysed. The colour of images captured by a digital camera, is often visually incorrect. Colorimetric calibration, at output-channel level, and correct exposure under a suitable illuminant can reduce errors substantially, but colour-rendering of certain colours remain anomalous, even after colorimetric correction, due to instrumental metamerism. Specific colours, are incorrectly captured, exhibiting a marked hue or chroma shift relative to other colours in the imaged scene. They originate from metameric differences in response at the spectral level. The potential size of metameric effects are tabulated, their cause is discussed and demonstrated, and a proposed method for its quantification, based on images of Colour Charts is described.
Color Perception Estimations of Metameric Pairs Under Different Illuminance Levels
Fibres and Textiles, 2022
LEDs or light emitting diodes of the lighting class dominate both the indoor and outdoor lighting industries today due to their accuracy and consumer-friendly color temperature. In the context of color science, it is necessary to analyze both the spectral power distribution of lighting and the human characteristics of color perception under these lights. In this article, we provide estimates of the appearance of eleven metameric pairs under LEDs with four correlated color temperatures and six illuminance levels, using color difference formulas based on the CIELAB, CAM02-UCS, and CAM16-UCS models to verify our estimates. We followed ASTM D4086 standard visual methods for detecting metamerism and for estimating the magnitude of a metameric color difference. Our investigations found that color appearance models are more reliable than CIELAB in evaluating color difference under various LED conditions. CAM16-UCS more accurately predicted the color difference estimates between all three f...
If surfaces from a scene are visually indistinguishable under one light, they may become distinguishable under another. The aim here was to test whether the frequency of such metamerism can be predicted by a statistical property of the colours of a scene, namely their conditional entropy. Simulations were based on 50 hyperspectral images of natural scenes under sunlight and north skylight. The correlation between the logarithm of the conditional frequency of metamerism and the conditional entropy of colours was strong, with r = 0.80–0.87. Additionally, the more likely that indistinguishable surfaces were distinguishable under a different daylight, the more reliable the prediction by conditional entropy.
CHROMATIC ADAPTATION AND METAMERIC PAIR EVALUATION
Color perception is influenced by the light source, the reflectance or transmittance properties of the object, the eye, and the brain. Color is one aspect of appearance. Gloss and texture are other aspects. It is well known, that perceived color of object changes if the illuminated light changes. The human visual systems attempt to compensate for the change in light source and hold the color constant. In Laboratory Color and Appearance Measurement was measured color appearance of set of colored paper chips under different illumination in a Datacolor TRU-VUE 2, Gretag Macbeth Judge II and LCAM LIGHT controlled lighting cabinet with approximate 0/45 illuminating/viewing geometry. In this work are presented results of comparison visual and instrumental assessments of twelve metameric pairs. It will be demonstrate influence of differences in relative spectral power distribution real light sources against tabulate data. Attention will be also focused on influence of chromatic adaptation time on perceived difference between evaluated samples.
Information limits on identification of natural surfaces by apparent colour
Perception, 2005
By adaptational and other mechanisms, the visual system can compensate for moderate changes in the colour of the illumination on a scene. Although the colours of most surfaces are perceived to be constant ("colour constancy"), some are not. The effect of these residual colour changes on the ability of observers to identify surfaces by their apparent colour was determined theoretically from high-resolution hyperspectral images of natural scenes under different daylights with correlated colour temperatures 4300 K, 6500 K, and 25000 K. Perceived differences between colours were estimated with an approximately uniform colour-distance measure. The information preserved under illuminant changes increased with the number of surfaces in the sample, but was limited to a relatively low asymptotic value, indicating the importance of physical factors in constraining identification by apparent colour.
Metamerism Index of Led Light on Halftone Colour Images
Acta Graphica, 2021
Skin face detection in photo imaging is an important component of systems for detecting similarities in visual perception, tracing faces through illumination and metamerism. This paper presents an evaluation of the skin perception under standardized conditions of varied light sources: cool-white fluorescent "store light", 6500K fluorescent "daylight", and incandescent "home light", Led light 6500 K, 2700K, 4000K CCT (Correlated colour temperature). In cases where the discrepancy is large, the resulting index of metamerism can be misleading. A small index of metamerism and a large change of color under illuminant metamerism has a different interpretation than what is perceived. This has been demonstrated through small colour variations in print through CMYK colors. The implication is that the particular indices of metameric should only account for a limited range under different light conditions. The method used in this paper is based on visual perception, which aims to work with a wide variety of individuals, under varying lighting conditions under the influence of standard daylight, but in this case we also used the Led light 6500K correlated colour temperature, and variations of skin color tones, comparing the illuminant metamerism of visual perception based on different reflectance power distributions (SPDs).
Fluctuating environmental light limits number of surfaces visually recognizable by colour
Scientific Reports, 2021
Small changes in daylight in the environment can produce large changes in reflected light, even over short intervals of time. Do these changes limit the visual recognition of surfaces by their colour? To address this question, information-theoretic methods were used to estimate computationally the maximum number of surfaces in a sample that can be identified as the same after an interval. Scene data were taken from successive hyperspectral radiance images. With no illumination change, the average number of surfaces distinguishable by colour was of the order of 10,000. But with an illumination change, the average number still identifiable declined rapidly with change duration. In one condition, the number after two minutes was around 600, after 10 min around 200, and after an hour around 70. These limits on identification are much lower than with spectral changes in daylight. No recoding of the colour signal is likely to recover surface identity lost in this uncertain environment.