Image encoding apparatus, image decoding apparatus, image encoding method, image decoding method, image encoding program, and image decoding program

An image decoding apparatus comprising:

• a decoding part for decoding coded data obtained by dividing a coding target image or a predictive residual image generated based on the coding target image, into predetermined transform blocks, performing transform coding of the coding target image or the predictive residual image in each unit of said transform block to output transform coefficients, quantizing the output transform coefficients on the basis of a quantization parameter to output quantized transform coefficients, and performing compression coding of coding-related information containing the quantized transform coefficients and the quantization parameter to yield coded data,
• wherein the decoding part has a function of converting the quantized transform coefficients in the coding target block to a one-dimensional string according to frequencies and decoding a zero run value being a number of consecutive coefficients providing 0 as an absolute value of the quantized transform coefficients in the one-dimensional string, a level value being an absolute value of a said quantized transform coefficient, and a positive/negative sign indicating whether the quantized transform coefficient is positive or negative, and comprises a decoded symbol memory for memorizing the coding-related information previously decoded;
• a decoding procedure provider for providing one or more types of decoding procedures;
• and a decoded data outputting part for selecting a decoding procedure which is one of the decoding procedures provided by the decoding procedure provider and which corresponds to a coding procedure used in the coding of the coding-related information as a decoding target, based on a predetermined coding procedure selection criterion, using the coding-related information previously decoded and stored in the decoded symbol memory, and for decoding the coding-related information on the basis of the selected decoding procedure to output decoded data,
• wherein, on the occasion of decoding the level value, the decoding procedure provider provides a decoding procedure corresponding to a coding procedure provided so as to set a shorter code length for a value closer to a level value at a frequency near a coding target level value.

An image decoding method comprising a decoding step of decoding coded data obtained by dividing a coding target image into macroblocks of a predetermined size, dividing each said macroblock into blocks of a predetermined shape and size specified based on a macroblock type, performing a motion compensated prediction in each unit of said block to output a motion vector, generating a predicted image from a reference image on the basis of the motion vector, calculating a difference between the predicted image and the coding target image to output a predictive residual image, performing transform coding of the predictive residual image in each unit of a predetermined transform block to output transform coefficients, quantizing the transform coefficients on the basis of a quantization parameter to output quantized transform coefficients, and performing compression coding of coding-related information containing the motion vector, the quantized transform coefficients, the macroblock type, and the quantization parameter to yield coded data,

• wherein the decoding step is to prepare one or more types of decoding procedures, select a decoding procedure which is one of said one or more types of decoding procedures and which corresponds to a coding procedure used in the coding of the coding-related information as a decoding target, based on a predetermined decoding procedure selection criterion, using the coding-related information previously decoded and stored in a decoded symbol memory, and decode the coding-related information on the basis of the selected decoding procedure to output decoded data,
• wherein the decoding step includes, for each of the predetermined transform blocks in a said macroblock, decoding coded block pattern information containing a nonzero coefficient existence flag indicating whether there exists a nonzero, said quantized transform coefficient, and
• wherein, on the occasion of decoding the coded block pattern information in a coding target macroblock, the decoding step includes providing a decoding procedure corresponding to a coding procedure provided so as to decrease a code length as a spatial correlation of the coded block pattern information becomes higher between the coding target macroblock and a neighboring macroblock thereto.

An image decoding method comprising:

• a decoding step of decoding coded data obtained by dividing a coding target image or a predictive residual image generated based on the coding target image, into predetermined transform blocks, performing transform coding of the coding target image or the predictive residual image in each unit of said transform block to output transform coefficients, quantizing the output transform coefficients on the basis of a quantization parameter to output quantized transform coefficients, and performing compression coding of coding-related information containing the quantized transform coefficients and the quantization parameter to yield coded data,
• wherein the decoding step is a step of converting the quantized transform coefficients in the coding target block to a one-dimensional string according to frequencies and decoding a zero run value being a number of consecutive coefficients providing 0 as an absolute value of the quantized transform coefficients in the one-dimensional string, a level value being an absolute value of the quantized transform coefficients, and a positive/negative code indicating whether the quantized transform coefficient is positive or negative, and is to prepare one or more types of decoding procedures, select a decoding procedure which is one of the one or more types of decoding procedures and which corresponds to a coding procedure used in the coding of the coding-related information as a decoding target, based on a predetermined coding procedure selection criterion, using the coding-related information previously decoded and stored in a decoded symbol memory, and decode the coding-related information on the basis of the selected decoding procedure to output decoded data,
• wherein, on the occasion of decoding the level value, the decoding step includes providing a decoding procedure corresponding to a coding procedure provided so as to set a shorter code length for a value closer to a level value at a frequency near a coding target level value.

A non-transitory computer readable storage medium storing an image decoding program for causing a computer to function as:

• decoding means for decoding coded data obtained by dividing a coding target image into macroblocks of a predetermined size, dividing each said macroblock into blocks of a predetermined shape and size specified based on a macroblock type, performing a motion compensated prediction in each unit of said block to output a motion vector, generating a predicted image from a reference image on the basis of the motion vector, calculating a difference between the predicted image and the coding target image to output a predictive residual image, performing transform coding of the predictive residual image in each unit of a predetermined transform block to output transform coefficients, quantizing the transform coefficients on the basis of a quantization parameter to output quantized transform coefficients, and performing compression coding of coding-related information containing the motion vector, the quantized transform coefficients, the macroblock type, and the quantization parameter to yield coded data,
• wherein the decoding means comprises a decoding procedure providing means for providing one or more types of decoding procedures;
• and decoded data outputting means for selecting a decoding procedure which is one of the decoding procedures provided by the decoding procedure providing means and which corresponds to a coding procedure used in the coding of the coding-related information as a decoding target, based on a predetermined decoding procedure selection criterion, using the coding-related information previously decoded and stored in a decoded symbol memory, and for decoding the coding-related information on the basis of the selected decoding procedure to output decoded data,
• wherein the decoding means has a function of, for each of the predetermined transform blocks in a said macroblock, decoding coded block pattern information containing a nonzero coefficient existence flag indicating whether there exists a nonzero, said quantized transform coefficient, and
• wherein, on the occasion of decoding the coded block pattern information in a coding target macroblock, the decoding procedure provider provides a decoding procedure corresponding to a coding procedure provided so as to decrease a code length as a spatial correlation of the coded block pattern information becomes higher between the coding target macroblock and a neighboring macroblock thereto.

A non-transitory computer readable storage medium storing an image decoding program for causing a computer to function as:

• decoding means for decoding coded data obtained by dividing a coding target image or a predictive residual image generated based on the coding target image, into predetermined transform blocks, performing transform coding of the coding target image or the predictive residual image in each unit of said transform block to output transform coefficients, quantizing the output transform coefficients on the basis of a quantization parameter to output quantized transform coefficients, and performing compression coding of coding-related information containing the quantized transform coefficients and the quantization parameter to yield coded data,
• wherein the decoding means comprises means for converting the quantized transform coefficients in the coding target block to a one-dimensional string according to frequencies and decoding a zero run value being a number of consecutive coefficients providing 0 as an absolute value of the quantized transform coefficients in the one-dimensional string, a level value being an absolute value of a said quantized transform coefficient, and a positive/negative sign indicating whether the quantized transform coefficient is positive or negative, and further comprises decoding procedure providing means for providing one or more types of decoding procedures;
• and decoded data outputting means for selecting a decoding procedure which is one of the decoding procedures provided by the decoding procedure providing means and which corresponds to a coding procedure used in the coding of the coding-related information as a decoding target, based on a predetermined coding procedure selection criterion, using the coding-related information previously decoded and stored in a decoded symbol memory, and for decoding the coding-related information on the basis of the selected decoding procedure to output decoded data,
• wherein, on the occasion of decoding the level value, the decoding procedure providing means provides a decoding procedure corresponding to a coding procedure provided so as to set a shorter code length for a value closer to a level value at a frequency near a coding target level value.