Decoding method and encoding method

An encoding method for encoding a Run symbol and a Level symbol to a variable length code using a table in which a code number corresponds to the Run symbol and the Level symbol, the Run symbol indicating the number of consecutive coefficients each having a value of zero, and the Level symbol indicating a value of a non-zero coefficient following the Run symbol, said encoding method comprising:

• deciding the Run symbol and the Level symbol;
• determining whether the Run symbol and the Level symbol belong to one of a first range and a predetermined range;
• obtaining a code number corresponding to the Run symbol and the Level symbol by referring to the table and encoding the obtained code number to a variable length code, when it is determined that the Run symbol and the Level symbol belong to the first range;
• and
• encoding the Level symbol to a variable length code and encoding the Run symbol to another variable length code, without referring to the table, when it is determined that the Run symbol and the Level symbol belong to the predetermined range,
• wherein the first range includes the Run and Level symbols that exist in the table, and
• the predetermined range includes Run and Level symbols corresponding to code numbers that are larger than code numbers corresponding to the Run and Level symbols in the first range,
• wherein said determining further includes determining whether the Run symbol and the level symbol belong to the second range,
• wherein the second range includes the Run and Level symbols corresponding to code numbers that are larger than the code numbers corresponding to the Run and Level symbols in the first range, and
• the predetermined range is a third range that includes the Run and Level symbols corresponding to code numbers that are larger than the code numbers corresponding to the Run and Level symbols in the second range, and
• said encoding method further comprising:
• calculating a code number corresponding to the Run symbol and the Level symbol by indirectly referring to the table and encoding the calculated code number to a variable length code, when it is determined that the Run symbol and the Level symbol belong to the second range.

An encoding method of encoding a Run symbol and a Level symbol to a variable length code using a table in which a code number corresponds to the Run symbol and the Level symbol, the Run symbol indicating the number of consecutive coefficients each having a value of zero, and the Level symbol indicating a value of a non-zero coefficient following the Run symbol, said encoding method comprising:

• deciding the Run symbol and the Level symbol;
• determining whether the Run symbol and the Level symbol belong to one of a first range and a predetermined range;
• obtaining a code number corresponding to the Run symbol and the Level symbol by referring to the table and encoding the obtained code number to a variable length code, when it is determined that the Run symbol and the Level symbol belong to the first range;
• and
• encoding the Level symbol to a variable length code and encoding the Run symbol to another variable length code, without referring to the table, when it is determined that the Run symbol and the Level symbol belong to the predetermined range,
• wherein the first range includes Run and Level symbols that exist in the table, and
• the predetermined range includes the Run and Level symbols corresponding to code numbers that are larger than code numbers corresponding to the Run and Level symbols in the first range,
• wherein the code numbers corresponding to the Run and Level symbols in the second range continue from the code numbers corresponding to the Run and Level symbols in the first range, and
• the code numbers corresponding to the Run and Level symbols in the third range continue from the code numbers corresponding to the Run and Level symbols in the second range.

A decoding apparatus which decodes a variable length code to a Run symbol and a Level symbol using a table in which a code number corresponds to the Run symbol and the Level symbol, the Run symbol indicating the number of consecutive coefficients each having a value of zero, and the Level symbol indicating a value of a non-zero coefficient following the Run symbol, said decoding apparatus comprising:

• a decoding unit operable to decode a variable length code to a code number;
• a determination unit operable to determine whether the code number obtained by said decoding unit belongs to a first range or a predetermined range;
• a decoding unit operable to decode the code number to a Run symbol and a Level symbol by referring to the table, when it is determined that the code number belongs to the first range, and
• a decoding unit operable to decode the code number to a Level symbol and then decoding a variable length code following the decoded variable length code to a Run symbol, without referring to the table, when it is determined that the code number belongs to the predetermined range,
• wherein the first range includes code numbers that exist in the table, and
• the predetermined range includes code numbers that are larger than the code numbers in the first range.

A computer readable medium including image data which is encoded and which is readable by a computer, said computer readable medium comprising:

• a variable length code sequence which indicates a Run symbol and a Level symbol,
• wherein a variable length code indicates a code number in a table in which the code number corresponds to the Run symbol and the Level symbol, and
• said variable length code sequence includes a variable length code which indicates a code number in a first range, a variable length code which indicates a code number in a second range, and a variable length code which indicates a code number in a third range, and
• wherein the first range includes code numbers that exist in the table,
• the second range includes code numbers that are larger than the code numbers in the first range, and
• the third range includes code numbers that are larger than the code numbers in the second range.