Methods and apparatus for preventing rounding errors when transform coefficients representing a motion picture signal are inversely transformed

An apparatus for pre-processing a set of transform coefficients, each of the transform coefficients having parity, to provide an error-immune set of transform coefficients for processing by an inverse orthogonal transform, the error-immune set of transform coefficients being immune to rounding errors when subject to the inverse orthogonal transform, the apparatus comprising:

• an accumulator, the accumulator receiving each of the transform coefficients in the set and providing a sum having parity;
• parity judgment means, receiving the sum from the accumulator, for judging the parity of the sum;
• parity inverting means, operating when the parity judgment means judges that the parity of the sum is even, for inverting the parity of one of the transform coefficients to provide a parity-inverted transform coefficient, the parity-inverted transform coefficient making the parity of the sum odd;
• and
• means for providing the transform coefficients including the parity-inverted transform coefficient as the error-immune set.

A method of inversely orthogonally transforming a set of transform coefficients without incurring rounding errors, each of the transform coefficients being represented by a binary number having a least-significant bit, the method comprising the steps of:

• determining the least-significant bit of each of the transform coefficients;
• counting the transform coefficients having a least-significant bit of one to provide a count;
• judging when the count is an even number;
• when the count is an even number, changing one of the transform coefficients to provide a changed transform coefficient, the changed transform coefficient making the count an odd number;
• and
• inversely orthogonally transforming the set of transform coefficients including the changed transform coefficient.

An apparatus for inversely orthogonally transforming a set of transform coefficients without incurring rounding errors, each of the transform coefficients having parity, the apparatus comprising:

• means for summing the transform coefficients to provide a sum, the sum having parity;
• parity judging means for judging the parity of the sum;
• sum oddifying means, operating when the parity judging means judges that the parity of the sum is even, for inverting the parity of one of the transform coefficients to provide a parity-inverted transform coefficient, the parity-inverted transform coefficient making the sum odd;
• and
• an inverse orthogonal transform circuit receiving the set of transform coefficients, including the parity-inverted transform coefficient, from the sum oddifying means.

An apparatus for inversely orthogonally transforming a set of transform coefficients without incurring rounding errors, each of the transform coefficients being represented by a binary number including a least-significant bit having a state, the state being one of a one state and a zero state, the apparatus comprising:

• least significant bit judging means for judging the state of the least-significant bit of each transform coefficient;
• counting means for providing a count by counting the transform coefficients whose least-significant bits are judged by the least-significant bit judging means to be in the one state;
• count judging means for judging when the count from the counting means is an even number;
• count oddifying means, operating when the count judging means judges that the count is an even number, for changing one of the transform coefficients to provide a changed transform coefficient, the changed transform coefficient making the count an odd number;
• and
• an inverse orthogonal transform circuit, receiving the set of transform coefficients, including the changed transform coefficient, from the count oddifying means.

An apparatus for compressing a motion picture signal, the motion picture signal including pictures, each picture being divided into blocks, the apparatus comprising:

• predictive coder means for predictively coding blocks of the motion picture signal by using matching blocks of a reference picture to form difference blocks;
• difference block encoding means for compressing the difference blocks from the predictive coder means to form a compressed motion picture signal, the difference block encoding means including:
• orthogonal transform means for orthogonally transforming the difference blocks from the predictive coder means to provide blocks of transform coefficients, and
• quantizing means for quantizing the blocks of transform coefficients from the orthogonal transform means to provide compressed signal blocks wherefrom the compressed motion picture signal is derived;
• local decoding means for expanding the compressed signal blocks from the difference block encoding means to provide restored difference blocks without incurring rounding errors when the compressed signal blocks are inversely orthogonally transformed, the local decoding means including:
• inverse quantizing means for inversely quantizing the compressed signal blocks from the difference block encoding means to provide blocks of restored transform coefficients, each of the restored transform coefficients having parity,
• means for summing the restored transform coefficients in each block of transform coefficients from the inverse quantizing means to provide a sum, the sum having parity,
• parity judging means for judging the parity of the sum,
• sum oddifying means, operating when the parity judging means judges that the parity of the sum is even, for inverting the parity of one of the restored transform coefficients in the block to provide a parity-inverted transform coefficient, the parity-inverted transform coefficient making the sum odd, and
• an inverse orthogonal transform circuit, receiving the block of restored transform coefficients, including the parity-inverted transform coefficient, from the sum oddifying means, the inverse orthogonal transform circuit providing the restored difference blocks;
• predictive decoder means for predictively decoding the restored difference blocks from the local decoding means to reconstruct picture blocks corresponding to the blocks of the motion picture signal;
• and
• a picture memory, the picture memory storing the reconstructed picture blocks from the predictive decoding means as blocks of a reconstructed picture for use as a reference picture for predictively coding other pictures of the motion picture signal.

An apparatus for compressing a motion picture signal, the motion picture signal including pictures, each picture being divided into blocks, the apparatus comprising:

• predictive coder means for predictively coding blocks of the motion picture signal by using matching blocks of a reference picture to form difference blocks;
• difference block encoding means for compressing the difference blocks from the predictive coder means to form a compressed motion picture signal, the difference block encoding means including:
• orthogonal transform means for orthogonally transforming the difference blocks from the predictive coder means to provide blocks of transform coefficients, and
• quantizing means for quantizing the blocks of transform coefficients from the orthogonal transform means to provide compressed signal blocks wherefrom the compressed motion picture signal is derived;
• local decoding means for expanding the compressed signal blocks from the difference block encoding means to provide restored difference blocks without incurring rounding errors when the compressed signal blocks are inversely orthogonally transformed, the local decoding means including;
• inverse quantizing means for inversely quantizing the compressed signal blocks from the difference block encoding means to provide blocks of restored transform coefficients, each of the restored transform coefficients being represented by a binary number including a least-significant bit,
• least-significant bit determining means for determining the least-significant bit of each of the restored transform coefficients,
• counting means for providing a count by counting the restored transform coefficients in each block having least-significant bits of one,
• count judging means for judging when the count from the counting means is an even number,
• count oddifying means, operating when the count judging means judges that the count is an even number, for changing one of the restored transform coefficients in the block to provide a changed transform coefficient, the changed transform coefficient making the count an odd number, and
• an inverse orthogonal transform circuit, receiving each block of restored transform coefficients, including the changed transform coefficient, from the count oddifying means, the inverse orthogonal transform circuit additionally providing the restored difference blocks;
• predictive decoder means for predictively decoding the restored difference blocks from the local decoding means to reconstruct picture blocks corresponding to the blocks of the motion picture signal;
• and
• a picture memory, the picture memory storing the reconstructed picture blocks from the predictive decoding means as blocks of a reconstructed picture for use as a reference picture for predictively coding other pictures of the motion picture signal.

An apparatus for expanding a compressed motion picture signal to provide a motion picture output signal, the compressed motion picture signal including signal portions each representing a picture of the motion picture output signal, the signal portions including variable-length coded compressed signal blocks, the apparatus comprising:

• an inverse variable-length coding means for applying inverse variable length coding to the variable-length coded compressed signal blocks to provide compressed signal blocks;
• decoding means for expanding the compressed signal blocks from the inverse variable-length coding means to provide restored difference blocks without incurring rounding errors when the compressed signal blocks are inversely orthogonally transformed, the decoding means including;
• inverse quantizing means for inversely quantizing each compressed signal block from the difference block encoding means to provide a block of restored transform coefficients, each of the restored transform coefficients having parity,
• means for summing the restored transform coefficients in the block of transform coefficients from the inverse quantizing means to provide a sum, the sum having parity,
• parity judging means for judging the parity of the sum,
• sum oddifying means, operating when the parity judging means judges that the parity of the sum is even, for inverting the parity of one of the restored transform coefficients in the block to provide a parity-inverted transform coefficient, the parity-inverted transform coefficient making the parity of the sum odd, and
• an inverse orthogonal transform circuit, receiving the block of restored transform coefficients, including the parity-inverted transform coefficient, from the sum oddifying means, the inverse orthogonal transform circuit providing the restored difference blocks.

An apparatus for expanding a compressed motion picture signal to provide a motion picture output signal, the compressed motion picture signal including signal portions each representing a picture of the motion picture output signal, the signal portions including variable-length coded compressed signal blocks, the apparatus comprising:

• an inverse variable-length coding means for applying inverse variable length coding to the variable-length coded compressed signal blocks to provide compressed signal blocks;
• decoding means for expanding the compressed signal blocks from the inverse variable-length coding means to provide restored difference blocks without incurring rounding errors when the compressed signal blocks are inversely orthogonally transformed, the decoding means including;
• inverse quantizing means for inversely quantizing each of the compressed signal blocks from the inverse variable-length coding means to provide a block of restored transform coefficients, each of the restored transform coefficients being represented by a binary number including a least-significant bit having a state, the state being one of a one state and a zero state,
• least-significant bit judging means for judging the state of the least-significant bit of each of the restored transform coefficients,
• counting means for providing a count by counting the transform coefficients in the block whose least-significant bits are judged by the least-significant bit judging means to be in the one state,
• count judging means for judging when the count from the counting means is an even number,
• count oddifying means, operating when the count judging means judges that the count is an even number, for changing one of the restored transform coefficients to provide a changed transform coefficient, the changed transform coefficient making the count an odd number, and
• an inverse orthogonal transform circuit, receiving the block of restored transform coefficients, including the changed transform coefficient, from the count oddifying means, the inverse orthogonal transform circuit additionally providing the restored difference blocks.

A method for compressing a motion picture signal to provide a compressed motion picture signal, the method comprising the steps of:

• detecting motion between blocks of a picture of the motion picture signal and blocks of a reconstructed picture serving as a reference picture;
• applying motion compensation to the reference picture in response to the motion detected by the detecting step to derive matching blocks of the reference picture;
• using the matching blocks of the reference picture to apply predictive coding to the blocks of the picture of the motion picture signal to provide blocks of differences;
• orthogonally transforming the blocks of differences to provide blocks of transform coefficients;
• deriving the compressed signal from the blocks of transform coefficients by applying quantizing and variable-length coding;
• prior to applying inverse orthogonal transform processing to the blocks of transform coefficients to provide blocks of restored differences, sum oddifying each block of transform coefficients to prevent rounding errors in the inverse orthogonal transform processing;
• and
• applying prediction decoding to the blocks of restored differences to provide picture blocks of an additional reconstructed picture for use as the reference picture in applying predictive coding to other pictures of the motion picture signal.