The von Kries hypothesis and a basis for color constancy

Color constancy is almost exclusively modeled with diagonal transforms. However, the choice of basis under which diagonal transforms are taken is traditionally ad hoc. Attempts to remedy the situation have been hindered by the fact that no joint characterization of the conditions for {sensors, illuminants, reflectances} to support diagonal color constancy has previously been achieved. In this work, we observe that the von Kries compatibility conditions are impositions only on the sensor measurements, not the physical spectra. This allows us to formulate the von Kries compatibility conditions succinctly as rank constraints on an order 3 measurement tensor. Given this, we propose an algorithm that computes a (locally) optimal choice of color basis for diagonal color constancy and compare the results against other proposed choices.Engineering and Applied Science

Kirschmann's Fourth Law

Kirschmann's Fourth Law states that the magnitude of simultaneous color contrast increases with the saturation of the inducing surround, but that the rate of increase reduces as saturation increases. Others since Kirschmann have agreed and disagreed. Here we show that the form of the relationship between simultaneous color contrast and inducer saturation depends on the method of measurement. Functions were measured by four methods: (i) asymmetric matching with a black surround, (ii) asymmetric matching with a surround metameric to equal energy white, (iii) dichoptic matching, and (iv) nulling an induced sinusoidal modulation. Results from the asymmetric matching conditions agreed with Kirschmann, whereas results from nulling and from dichoptic matching showed a more linear increase in simultaneous contrast with the saturation of the inducer. We conclude that the method certainly affects the conclusions reached, and that there may not be any "fair" way of measuring simultaneous contrast

Early infant feeding and adiposity risk: from infancy to adulthood

Introduction: Systematic reviews suggest that a longer duration of breast-feeding is associated with a reduction in the risk of later overweight and obesity. Most studies examining breast-feeding in relation to adiposity have not used longitudinal analysis. In our study, we aimed to examine early infant feeding and adiposity risk in a longitudinal cohort from birth to young adulthood using new as well as published data. Methods: Data from the Western Australian Pregnancy Cohort (Raine) Study in Perth, W.A., Australia, were used to examine associations between breast-feeding and measures of adiposity at 1, 2, 3, 6, 8, 10, 14, 17, and 20 years. Results: Breast-feeding was measured in a number of ways. Longer breast-feeding (in months) was associated with reductions in weight z-scores between birth and 1 year (β = -0.027; p \u3c 0.001) in the adjusted analysis. At 3 years, breast-feeding for \u3c4 months increased the odds of infants experiencing early rapid growth (OR 2.05; 95% CI 1.43-2.94; p \u3c 0.001). From 1 to 8 years, children breast-fed for ≤4 months compared to ≥12 months had a significantly greater probability of exceeding the 95th percentile of weight. The age at which breast-feeding was stopped and a milk other than breast milk was introduced (introduction of formula milk) played a significant role in the trajectory of the BMI from birth to 14 years; the 4-month cutoff point was consistently associated with a higher BMI trajectory. Introduction of a milk other than breast milk before 6 months compared to at 6 months or later was a risk factor for being overweight or obese at 20 years of age (OR 1.47; 95% CI 1.12-1.93; p = 0.005). Discussion: Breast-feeding until 6 months of age and beyond should be encouraged and is recommended for protection against increased adiposity in childhood, adolescence, and young adulthood. Adverse long-term effects of early growth acceleration are fundamental in later overweight and obesity. Formula feeding stimulates a higher postnatal growth velocity, whereas breast-feeding promotes slower growth and a reduced likelihood of overweight and obesity. Biological mechanisms underlying the protective effect of breast-feeding against obesity are based on the unique composition and metabolic and physiological responses to human milk

Limits to the salience of ultraviolet: Lessons from colour vision in bees and birds

Publisher version: http://jeb.biologists.org/content/204/14/2571/F1.expansio

Information Flow in Color Appearance Neural Networks

Color Appearance Models are biological networks that consist of a cascade of linear+nonlinear layers that modify the linear measurements at the retinal photo-receptors leading to an internal (nonlinear) representation of color that correlates with psychophysical experience. The basic layers of these networks include: (1) chromatic adaptation (normalization of the mean and covariance of the color manifold), (2) change to opponent color channels (PCA-like rotation in the color space), and (3) saturating nonlinearities to get perceptually Euclidean color representations (similar to dimensionwise equalization). The Efficient Coding Hypothesis argues that these transforms should emerge from information-theoretic goals. In case this hypothesis holds in color vision, the question is, what is the coding gain due to the different layers of the color appearance networks? In this work, a representative family of Color Appearance Models is analyzed in terms of how the redundancy among the chromatic components is modified along the network and how much information is transferred from the input data to the noisy response. The proposed analysis is done using data and methods that were not available before: (1) new colorimetrically calibrated scenes in different CIE illuminations for proper evaluation of chromatic adaptation, and (2) new statistical tools to estimate (multivariate) information-theoretic quantities between multidimensional sets based on Gaussianization. Results confirm that the Efficient Coding Hypothesis holds for current color vision models, and identify the psychophysical mechanisms critically responsible for gains in information transference: opponent channels and their nonlinear nature are more important than chromatic adaptation at the retina

Modelling colour constancy in fish: implications for vision and signalling in water

Colour vision and colour signals are important to aquatic animals, but light scattering and absorption by water distorts spectral stimuli. To investigate the performance of colour vision in water, and to suggest how photoreceptor spectral sensitivities and body colours might evolve for visual communication, we model the effects of changes in viewing distance and depth on the appearance of fish colours for three teleosts: a barracuda, Syphraena helleri, which is dichromatic, and two damselfishes, Chromis verater and C. hanui, which are trichromatic. We assume that photoreceptors light-adapt to the background, thereby implementing the von Kries transformation, which can largely account for colour constancy in humans and other animals, including fish. This transformation does not however compensate for light scattering over variable viewing distances, which in less than a metre seriously impairs dichromatic colour vision, and makes judgement of colour saturation unreliable for trichromats. The von Kries transformation does substantially offset colour shifts caused by changing depth, so that from depths of 0 to 30m modelled colour changes (i.e. failures of colour constancy) are sometimes negligible. However, the magnitudes and directions of remaining changes are complex, depending upon the specific spectral sensitivities of the receptors and the reflectance spectra. This predicts that when judgement of colour is important, the spectra of signalling colours and photoreceptor spectral sensitivities should be evolutionarily linked, with the colours dependent on photoreceptor spectral sensitivities, and vice versa

A mathematical theory of evidence for G.L.S. Shackle

Evidence Theory is a branch of mathematics that concerns the combination of empirical evidence in an individual's mind in order to construct a coherent picture of reality. Designed to deal with unexpected empirical evidence suggesting new possibilities, evidence theory has a lot in common with Shackle's idea of decision-making as a creative act. This essay investigates this connection in detail, pointing to the usefulness of evidence theory to formalise and extend Shackle's decision theory. In order to ease a proper framing of the issues involved, evidence theory is not only compared with Shackle's ideas but also with additive and sub-additive probability theories. Furthermore, the presentation of evidence theory does not refer to the original version only, but takes account of its most recent developments, too.

Color-appearance modeling for cross-media image reproduction

Five color-appearance transforms were tested under a variety of conditions to determine which is best for producing CRT reproductions of original printed images. The transforms included: von Kries chromatic adaptation, CIELAB color space, RLAB color appearance model, Hunt\u27s color appearance model, and Nayatani\u27s color appearance model. It was found that RLAB produced the best matches for changes in white point, luminance level, and background changes, but did not accurately predict the effect of surround. The ability of CIELAB color space was equal to that of RLAB in many cases, and performed better for changes in surround. Expert observers generated CRT images in one viewing condition that they perceived to match an original image viewed in another condition. This technique produced images that were equal to or better than the best color appearance model tested and is a useful technique to generate color appearance data for developing new models and testing existing models