The Planck length and the constancy of the speed of light in five dimensional space parametrized with two time coordinates

In relativity and quantum field theory, the vacuum speed of light is assumed to be constant; the range of validity of general relativity is determined by the Planck length. However, there has been no convincing theory explaining the constancy of the light speed. In this paper, we assume a five dimensional spacetime with three spatial dimensions and two local time coordinates giving us a hint about the constancy of the speed of light. By decomposing the five dimensional spacetime vector into four-dimensional vectors for each time dimension and by minimizing the resulting action, for a certain class of additional time dimensions, we observe the existence of a minimal length scale, which we identify as the Planck scale. We derive an expression for the speed of light as a function of space and time and observe the constancy of the vacuum speed of light in the observable universe

Convolutional Color Constancy

Color constancy is the problem of inferring the color of the light that illuminated a scene, usually so that the illumination color can be removed. Because this problem is underconstrained, it is often solved by modeling the statistical regularities of the colors of natural objects and illumination. In contrast, in this paper we reformulate the problem of color constancy as a 2D spatial localization task in a log-chrominance space, thereby allowing us to apply techniques from object detection and structured prediction to the color constancy problem. By directly learning how to discriminate between correctly white-balanced images and poorly white-balanced images, our model is able to improve performance on standard benchmarks by nearly 40%

Photometric, geometric and perceptual factors in illumination-independent lightness constancy

It has been shown that lightness constancy depends on the articulation of the visual field (Agostini & Galmonte, 1999). However, among researchers there is little agreement about the meaning of “articulation.” Beyond the terminological heterogeneity, an important issue remains: What factors are relevant for the stability of surface color perception? Using stimuli with two fields of illumination, we explore this issue in three experiments. In Experiment 1, we manipulated the number of luminances, the number of reflectances, and the number of surfaces and their spatial relationships; in Experiment 2, we manipulated the luminance range; finally, in Experiment 3 we varied the number of surfaces crossed by the illumination edge. We found that there are two relevant factors in optimizing lightness constancy: (1) the lowest luminance in shadow and (2) the co-presence of patches of equal reflectance in both fields of illumination. The latter effect is larger if these patches strongly belong to each other. We interpret these findings within the albedo hypothesis

Relational color constancy in achromatic and isoluminant images

Relational color constancy, which refers to the constancy of perceived relations between surface colors under changes in illuminant, may be based on the computation of spatial ratios of cone excitations. As this activity need occur only within rather than between cone pathways, relational color constancy might be assumed to be based on relative luminance processing. This hypothesis was tested in a psychophysical experiment in which observers viewed simulated images of Mondrian patterns undergoing colorimetric changes that could be attributed either to an illuminant change or to a nonilluminant change; the images were isoluminant, achromatic, or unmodified. Observers reliably discriminated the two types of changes in all three conditions, implying that relational color constancy is not based on luminance cues alone. A computer simulation showed that in these isoluminant and achromatic images spatial ratios of cone excitations and of combinations of cone excitations were almost invariant under illuminant changes and that discrimination performance could be predicted from deviations in these ratios.Biotechnology and Biological Sciences Research Council (BBSRC

Can illumination estimates provide the basis for color constancy?

Objects hardly appear to change color when the spectral distribution of the illumination changes: a phenomenon known as color constancy. Color constancy could either be achieved by relying on properties that are insensitive to changes in the illumination (such as spatial color contrast) or by compensating for the estimated chromaticity of the illuminant. We examined whether subjects can judge the illuminant's color well enough to account for their own color constancy. We found that subjects were very poor at judging the color of a lamp from the light reflected by the scene it illuminated. They were much better at judging the color of a surface within the scene. We conclude that color constancy must be achieved by relying on relationships that are insensitive to the illumination rather than by explicitly judging the color of the illumination. © ARVO

The science of color and color vision

A survey of color science and color vision

Variational Disparity Estimation Framework for Plenoptic Image

This paper presents a computational framework for accurately estimating the disparity map of plenoptic images. The proposed framework is based on the variational principle and provides intrinsic sub-pixel precision. The light-field motion tensor introduced in the framework allows us to combine advanced robust data terms as well as provides explicit treatments for different color channels. A warping strategy is embedded in our framework for tackling the large displacement problem. We also show that by applying a simple regularization term and a guided median filtering, the accuracy of displacement field at occluded area could be greatly enhanced. We demonstrate the excellent performance of the proposed framework by intensive comparisons with the Lytro software and contemporary approaches on both synthetic and real-world datasets