METHODS AND APPARATUS FOR PREVENTING ROUNDING ERRORS WHEN TRANSFORM COEFFICIENTS REPRESENTING A MOTION PICTURE SIGNAL ARE INVERSELY TRANSFORMED

摘要

Mismatch error occur in the local decoder of a MPEG-standard compressor for amotion picture signal, and in an MPEG-standardexpander for a compressed motion picture signal. This is because of the lackof a standard for rounding results of *.5 (* is an integer)obtained when a set of transform coefficients resulting from compressing themotion picture signal is inversely orthogonally transformed.The invention prevents mismatch errors by preprocessing the set of transformcoefficients prior to the inverse othogonal transform (15).The transform coefficients in the set are summed (23A) and the parity (odd oreven) of the sum is judged (21). When the parity of thesum is judged to be even, the parity of one of the transform coefficients inthe set is inverted (28) to provide a parity-inverted transformcoefficient. This makes the parity of the sum odd. Then, when the set oftransform coefficients indluding the parity-inverted transformcoefficient is inversely orthogonally transformed (15), none of the results ofthe orthogonal transform will have a value of *.5.