| 摘要 |
PURPOSE:To speed up a processing and to accurately determine the upper limit value and the lower limit value of the gradation correction of an input picture signal by obtaining a histogram at the time of obtaining the said values by using R, G-values and determining the upper limit value and the lower limit value from a cumulative distribution. CONSTITUTION:C, M, and Y-data to which their characteristics are converted by a gamma correction circuit 24, are inputted to a masking circuit 26, where irregular color components and ground color are eliminated to obtain chro minance signals C, M, Y, and BK. Then they are respectively converted to analog signals by D/A converters 28C, 28M, 28Y, and 28BK. The sampling by an A/D converter 16 is executed in the direction perpendicular to the horizon tal scanning direction, and by sequentially moving the position in the horizontal scanning direction the entire picture is sampled. The histogram is obtained by using the signal level of the brightness signal Y at the said sampling points to determine dark points and highlight points. In such a way, the dark points and the highlight points can be accurately obtained by a simple calculation at the high speed.
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