Occlusions and their relationship with the distribution of contrasts in natural images

AbstractAn Information-Theory-like hypothesis recently proposed for early visual processing (the Minimal Local-Asperity hypothesis) accounts for the adaptive behavior with intensity of horizontal cells. It has been shown that for this to hold, the probability that a point is traversed by an occluding border must increase supralinearly (that is, with a positive second derivative) as a function of contrast. We test this condition by analyzing the distribution of contrasts and their relationship with occluding borders in natural images. We find that the distribution of contrasts in natural images falls exponentially as a function of contrast. Moreover, the probability that a point is traversed by an occluding border in natural images always rises with contrast until reaching one. This rise tends to be supralinear and addition of noise (at low intensities) increases the supralinearity, shifting the rising portion of the curve towards higher contrasts. These findings lend support to the Minimal Local-Asperity hypothesis, which proposes that one of the main roles of early retinal processing is to extract optimally edge, contrast, and luminance attributes from the visual world based on previous knowledge about natural images

Colour measurement of natural stones using a calibrated digital camera

Natural stones (marbles, granites, etc.) are used as building materials like ceramic tiles and artificial stones. In this work, we evaluate whether automatic natural-stone classification can be performed based on colorimetric calibration and S-CIELAB model of human colour perception. We found significant differences between the histograms of the ΔE S-CIELAB model from different marble types, which might be taken into account on industrial applications.This work was supported by the Spanish Ministerio de Educación y Ciencia from the Ramón y Cajal Program Grant 2904/01 to R.M.B., and by the Spanish Generalitat Valenciana CoreGrant CTBCDPT/04/006 to the University of Alicante