To detect a level difference in strip patterns generated in a gradation region within a displayed image due to roughness of quantization of video signals.
A signal passed through a horizontal HPF circuit A11 detects, as a horizontal flat region, a region where pixel-value differences are within a fixed range by means of a horizontal detection circuit A15. Then, the signal determines a boundary line in a horizontal direction of the region detected, and judges the boundary line as the level difference within the gradation region when the pixel-value differences or a rate (gradient) of a pixel-value change in the vicinity of the boundary line are within the predetermined range. Similarly, a signal passed through a vertical detection HPF circuit A12 detects a vertical flat region by means of a vertical detection circuit A16, and determines a boundary line in the vertical direction of the region detected to thereby judge from a pixel-value difference or a rate (gradient) of pixel-value change in the vicinity of the boundary line, whether the boundary line is a level difference within the gradation region or not.
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YAMAGUCHI TATSUO
Satoshi Kono
Makoto Nakamura
Kurata Masatoshi
Takashi Mine
Yoshihiro Fukuhara
Sadao Muramatsu
Ryo Hashimoto