Image coding and decoding apparatus, method of image coding and decoding, and recording medium for recording program for image coding and decoding

A digital still camera for decoding a code string, the code string including a plurality of entropy codes, the entropy codes being generated by orthogonally transforming, quantizing and entropy coding each pixel of a block, the block including a predetermined number of pixels and being obtained by dividing image data, the digital still camera comprising:

• a first storage unit operable to store the code string;
• an entropy decoding unit operable to extract an entropy code from the first storage unit, entropy decoding the extracted entropy code to generate a coefficient corresponding to the entropy code;
• a coefficient generation unit operable to generate an orthogonal transform coefficient based on the generated coefficient;
• a second storage unit operable to store the generated orthogonal transform coefficient;
• a decoding control unit operable to direct, after the generated coefficient has been processed by the coefficient generation unit and the second storage unit, the entropy decoding unit to extract a next entropy code and perform entropy decoding for the newly extracted entropy code;
• an inverse orthogonal transformation unit operable to read the orthogonal transform coefficient from the second storage unit, and convert the orthogonal transform coefficient to generate a plurality of blocks;
• and
• a display unit operable to generate image data from the newly generated blocks, and display the newly generated image data,
• wherein the entropy decoding unit includes:
• a code string storing subunit operable to store a code string including an entropy code, the entropy code being generated by coding a coefficient relating to the image data;
• a decoding table containing a coefficient corresponding to an entropy code;
• a code specifying table containing entry information showing an entropy code corresponding to a coefficient, the entry information including compressed information and uncompressed information, the compressed information being generated by run-length compressing a part of the entropy code and showing a bit length of the run-length compressed part, and the uncompressed information showing another part of the entropy code aside from the run-length compressed part;
• a run-length obtaining subunit operable to obtain a run-length of a run included in the code string, the run being a bit string of consecutive, same sign bits starting from a predetermined bit location;
• a bit length obtaining subunit operable to obtain from the code specifying table the uncompressed information corresponding to the compressed information showing a same bit length as the obtained run-length;
• a specifying subunit operable to specify, as the entropy code, a bit string that starts from the predetermined bit location and that has a length determined based on the obtained run-length and the length shown by the obtained uncompressed information;
• and
• a decoding subunit operable to obtain from the decoding table a coefficient corresponding to the specified entropy code.

An image decoding method for use by an image decoding apparatus that performs restoring of image data by decoding an entropy code to generate a coefficient relating to the image data, the entropy code being a bit pattern of which bit length is variable depending on occurrence probability of the coefficient, the image decoding apparatus including:

• a code string storing unit operable to store a code string including an entropy code, the entropy code being generated by coding a coefficient relating to the image data;
• a decoding table containing a coefficient corresponding to an entropy code;
• and a code specifying table containing entry information showing an entropy code corresponding to a coefficient, the entry information including compressed information and uncompressed information, the compressed information being generated by run-length compressing a part of the entropy code and showing a bit length of the run-length compressed part, and the uncompressed information showing another part of the entropy code aside from the run-length compressed part,
• the image decoding method comprising:
• a run-length obtaining step of obtaining a run-length of a run included in the code string, the run being a bit string of consecutive, same sign bits starting from a predetermined bit location;
• a bit length obtaining step of obtaining from the code specifying table uncompressed information corresponding to compressed information showing a same bit length as the obtained run-length;
• a specifying step of specifying, as the entropy code, a bit string that starts from the predetermined bit location and that has a length determined based on the obtained run-length and the length shown by the obtained uncompressed information;
• and
• a decoding step of obtaining from the decoding table a coefficient corresponding to the specified entropy code.

An image decoding program for execution by a computer and for use by an image decoding apparatus that performs restoring of image data by decoding an entropy code to generate a coefficient relating to the image data, the entropy code being a bit pattern of which bit length is variable depending on occurrence probability of the coefficient, the image decoding apparatus including:

• a code string storing unit operable to store a code string including an entropy code, the entropy code being generated by coding a coefficient relating to the image data;
• a decoding table containing a coefficient corresponding to an entropy code;
• and a code specifying table containing entry information showing an entropy code corresponding to a coefficient, the entry information including compressed information and uncompressed information, the compressed information being generated by run-length compressing a part of the entropy code and showing a bit length of the run-length compressed part, and the uncompressed information showing another part of the entropy code aside from the run-length compressed part,
• the image decoding program comprising:
• program code operable to cause the computer to obtain a run-length of a run included in the code string, the run being a bit string of consecutive, same sign bits starting from a predetermined bit location;
• program code operable to cause the computer to obtain from the code specifying table uncompressed information corresponding to compressed information showing a same bit length as the obtained run-length;
• program code operable to cause the computer to specify as the entropy code, a bit string that starts from the predetermined bit location and that has a length determined based on the obtained run-length and the length shown by the obtained uncompressed information;
• and
• program code operable to cause the computer to obtain from the decoding table a coefficient corresponding to the specified entropy code.

A computer-readable medium storing an image decoding program for use by an image decoding apparatus that performs restoring of image data by decoding an entropy code to generate a coefficient relating to the image data, the entropy code being a bit pattern of which bit length is variable depending on occurrence probability of the coefficient, the image decoding apparatus including:

• a code string storing unit operable to store a code string including an entropy code, the entropy code being generated by coding a coefficient relating to the image data;
• a decoding table containing a coefficient corresponding to an entropy code;
• and a code specifying table containing entry information showing an entropy code corresponding to a coefficient, the entry information including compressed information and uncompressed information, the compressed information being generated by run-length compressing a part of the entropy code and showing a bit length of the run-length compressed part, and the uncompressed information showing another part of the entropy code aside from the run-length compressed part,
• the image decoding program comprising:
• a run-length obtaining step of obtaining a run-length of a run included in the code string, the run being a bit string of consecutive, same sign bits starting from a predetermined bit location;
• a bit length obtaining step of obtaining from the code specifying table uncompressed information corresponding to compressed information showing a same bit length as the obtained run-length;
• a specifying step of specifying, as the entropy code, a bit string that starts from the predetermined bit location and that has a length determined based on the obtained run-length and the length shown by the obtained uncompressed information;
• and
• a decoding step of obtaining from the decoding table a coefficient corresponding to the specified entropy code.