Video contrast enhancer
 A video contrast enhancer enhances luminance contrast by dividing each video frame or field into blocks, calculating a mean luminance level for each block, selecting mapping functions on the basis of these mean luminance levels over a series of frames or fields, and mapping the video luminance levels according to the selected mapping functions. Color-saturation contrast is enhanced by modifying the amplitude of the modulated chrominance signal by the histogram equalization method, preferably by making a single linear modification in each period of the chrominance signal, so that color phase is not affected. For video signals with non-picture bands, these enhancements are preferably restricted to the picture area. If a black offset is present, it is preferably removed. 
Mitsubishi Denki Kabushiki Kaisha
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Hitoshi Shinji Masayuki Hiroshi Yuuji Naohiro Takuji
Hasegawa Takeuchi Tsuji Onishi Yamamoto Fujimura Kurashita