Method and apparatus of local contrast enhancement

Abstract

Methods and apparatuses of contrast enhancement on an image are disclosed. The method performs local shading of fine contrast variations in an image, with particular advantage in tone mapping applications. The amounts of shading are determined by the preferred degree of increased image contrast 810, including compensation for subsequent tone mapping, and the difference between a profile signal 803 and the image signal 801 conditional on the signal profile level being higher than the original image signal level, wherein avoiding boosting of brightness level to obtain contrast enhancement. The profile signal 803 is calculated by the weighted sum of the image signal and the absolute signal variation which is the absolute value of the variation between the brightness of two neighbor pixels. This amount of shading is reduced to zero when the profile signal 803 is lower than the original image signal 801 for avoiding the overshooting problem at sharp edges in an image. Uniform RGB scaling is applied to preserve original color tones.

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