Importance

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Abstract

A circuit it for deciding classes resulting from 8.times.8 DCT or 2.times.4.times.8 DCT blocks includes a block forming circuit for converting a digital video signal into a predetermined block structure, a mode deciding section for detecting still/motion of the digital video signal block to generate a mode signal, a DCT section for selectively performing the 8.times.8 DCT or 2.times.4.times.8 DCT upon the block supplied from the block forming circuit according to the mode signal of the mode deciding section, a controlling section for controlling DCT data coefficients output according to the mode signal from mode deciding section, a scanning section for zig-zag scanning data in an 8.times.8 activity detecting pattern upon the output of the 8.times.8 DCT block from the DCT section and zig-zag scanning data in a 2.times.4.times.8 activity detecting pattern upon the output of the 2.times.4.times.8 DCT block under the control of the controlling section, a comparative circuit for comparing the data coefficient values from the scanning section with threshold values of a predetermined number, and a class deciding section for deciding the classes according to the comparison values from the comparative circuit. Thus, the class of corresponding block is decided by using the activity detecting pattern differently produced by the 8.times.8 DCT block and 2.times.4.times.8 DCT block to minimize loss of a horizontal edge of the 2.times.4.times.8 DCT block, thereby preventing degradation of picture quality.

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First Claim