Study on feature extraction and filling-in process in visual system

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(1) We tried to apply the model which can explain some brightness illusions to the real image in order to examine why visual illusion occurs in the visual system. As a result, it is suggested that the mechanism which produces the brightness illusion is concerned in focusing and fusion of the binocular retinal images.(2) Retinal cones play an important role in light adaptation. To understand the light adaptation, it is necessary to consider characteristics of the cone. The light intensity-response curve for the cone is a S-shape curve. We employ this curve to enhance a contrast of digital images. This method can improve some problems of previous enhance methods.(3) Overall (average) adaptation and local adaptation exist in human visual system. In addition, a physiological experiment suggests that the midrange adaptation may occur in human visual system. The present study was carried out to examine the existence and the characteristics of the midrange adaptation by comparing subjective brightness of two spots. The results indicate that the midrange adaptation occurs when a step change in luminance exists on the fovea, but not when it exists out of the fovea.(4) In order to understand that the subjective circle is brighter than the background, we measured the perceived brightness of the part which faces line end and part which faces the parallel side of the stripe. With decreasing line interval, the perceived brightness of the line end (parallel side) is brighter (darker).(5) We apply the midrange adaptation and S-shape curve of the cone to high dynamic range images (over 60dB). Both contrast of bright region and dark region was improved.