Picture encoding method and apparatus, picture decoding method and apparatus and furnishing medium

A picture encoding method for encoding a picture on a block basis in which, before encoding coefficients specifying the state of a picture by discrete cosine transform executed on a block basis constituted by a luminance block and a chrominance block, reference is had to coefficients of a neighboring block to effect predictive coding, wherein

• the position and number of blocks used for prediction of AC coefficients and DC coefficients by said discrete cosine transform is changed responsive to a format flag indicating a picture format adapted for setting the type and the number of chrominance pixels allocated to the luminance pixels constituting said luminance block.

A picture encoding apparatus for encoding a picture on a block basis constituted by a luminance block and a chrominance block, comprising:

• means for adding a format flag to said picture for indicating a picture format of said picture;
• means for adding a first coefficient flag to said picture for indicating whether or not there exist one or more coefficients to be encoded in each said chrominance block;
• means for selectively adding a second coefficient flag to said picture for indicating in detail whether or not there exist one or more coefficients to be encoded in said chrominance block depending on said format flag and said first coefficient flag, where the second coefficient flag is not added if the first coefficient flag indicates no coefficients exist in each said chrominance block and the value of the second coefficient flag depends on the values of the format flag and the first coefficient flag.

A picture encoding apparatus for encoding a picture on a block basis in which, before encoding coefficients specifying the state of a picture by discrete cosine transform executed on a block basis constituted by a luminance block and a chrominance block, reference is had to coefficients of a neighboring block to effect predictive coding, comprising:

• encoding means for performing the encoding as the position and number of blocks used for prediction of AC coefficients and DC coefficients by said discrete cosine transform is changed responsive to a format flag indicating a picture format adapted for setting the type and the number of chrominance pixels allocated to the luminance pixels constituting said luminance block.

A picture decoding method for decoding a picture on a block basis in which encoded picture data obtained by having reference to coefficients of a neighboring block to effect predictive coding before encoding coefficients specifying the state of a picture by discrete cosine transform executed on a block basis is decoded, each of said blocks being made up of a luminance block and a chrominance block, wherein

• the position and number of blocks used for prediction of AC coefficients and DC coefficients by said discrete cosine transform is set responsive to a format flag indicating a picture format adapted for setting the type and the number of chrominance pixels allocated to the luminance pixels constituting said luminance block.

A picture decoding apparatus for decoding a picture on a block basis in which encoded picture data obtained by having reference to coefficients of a neighboring block to effect predictive coding before encoding coefficients specifying the state of a picture by discrete cosine transform executed on a block basis is decoded, each of said blocks being made up of a luminance block and a chrominance block, comprising:

• decoding means for decoding the encoded picture data as the position and number of blocks used for prediction of AC coefficients and DC coefficients by said discrete cosine transform is set responsive to a format flag indicating a picture format adapted for setting the type and the number of chrominance pixels allocated to the luminance pixels constituting said luminance block.

A furnishing medium for furnishing encoded picture data encoded on a block basis constituted by a luminance block and a chrominance block, wherein the encoded picture data furnished has been generated by:

• adding a format flag to said picture for indicating a picture format of said picture;
• adding a first coefficient flag to said picture for indicating whether or not there exist one or more coefficients to be encoded in each said chrominance block;
• selectively adding a second coefficient flag to said picture for indicating in detail whether or not there exist one or more coefficients to be encoded in said chrominance block depending on said format flag and said first coefficient flag, where the second coefficient flag is not added if the first coefficient flag indicates no coefficients exist in each said chrominance block and the value of the second coefficient flag depends on the values of the format flag and the first coefficient flag.

A furnishing medium for furnishing encoded picture data obtained by having reference to coefficients of a neighboring block to effect predictive coding before encoding coefficients specifying the state of a picture by discrete cosine transform executed on a block basis, each of said blocks being made up of a luminance block and a chrominance block, wherein

• the encoded picture data is furnished as the position and number of blocks used for prediction of AC coefficients and DC coefficients by said discrete cosine transform is set responsive to a format flag indicating a picture format adapted for setting the type and the number of chrominance pixels allocated to the luminance pixels constituting said luminance block.