| 摘要 |
PURPOSE: A predictive coding method in MPEG-4 is provided to improve coding performance while maintaining compatibility with conventional predictive coding method. CONSTITUTION: A value that maintains the optimal state when an image is coded according to the size of the image is set to a threshold value. Absolute values of horizontal and vertical slope values with respect to a block prior to the block to be currently predictive-coded are obtained, and than the absolute value of the difference between the two absolute values is acquired. The absolute value of the difference is compared with the threshold value(20). When the threshold value is smaller than the absolute value while the absolute value of the vertical slope is larger than the absolute value of the horizontal slope, the first direction information is generated. The second direction information is created when the threshold value is smaller than the absolute value of the difference while the absolute value of the vertical slope is smaller than the absolute value of the horizontal slope. When the threshold value is larger than the absolute value of the difference, the third direction information is created. Upon the generation of the first direction information, the horizontal AC coefficient of the prior block is used for a predictor of the current block(23). When the second direction information is generated, the vertical AC coefficient of the prior block is used for the predictor of the current block(22). Upon the creation of the third direction information, the horizontal and vertical AC coefficients of the prior block are used for the predictor of the current block(24).
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