Image encoder

An image coding method for coding each block of a digital image divided into two-dimensional blocks, each block having a plurality of pixels, the method comprising:

• determining a coding mode for a target block to output mode information of the target block;
• fetching a codeword of the mode information of the target block from a codeword table to output, based on a combination of the mode information of the target block and the mode information of previously coded blocks at a periphery of the target block including temporary mode information as the mode information of the blocks at the periphery of the target block when the blocks at the periphery are out of an image, the codeword table having codewords, each codeword being determined based on a combination of the mode information of the target block and the mode information of the previously coded blocks at the periphery of the target block;
• or a combination of the mode information of the target block and temporary mode information as a substitute for the mode information of the blocks at the periphery of the target block when the blocks at the periphery are out of an image;
• and
• coding pixel data in the target block according to the mode information of the target block.

An image coding apparatus for coding each block of a digital image divided into two-dimensional blocks, each block having a plurality of pixels, said apparatus comprising:

• a mode information determining section that is configured to determine a coding mode for a target block to output information of the target block;
• a mode information coding section that is configured to output, as a codeword of the mode information of the target block, the codeword that is determined based on a combination of the mode information of the target block and the mode information of previously coded blocks at the periphery of the target block, or a combination of the mode information of the target block and temporary mode information as a substitute for the mode information of the blocks at the periphery of the target block when the blocks at the periphery are out of an image;
• and
• a block data coding section that is configured to code pixel data in the target block according to the mode information of the target block.

An image coding apparatus for coding each block of a digital image divided into two-dimensional blocks, each block having a plurality of pixels, said apparatus comprising:

• a mode information determining section that is configured to determine a coding mode for a target block to output mode information of the target block;
• a mode information coding section that is configured to fetch and output a codeword of the mode information of the target block from a codeword table, based on a combination of the mode information of the target block and mode information of previously coded blocks at the periphery of the target block including temporary mode information as the mode information of the blocks at the periphery of the target block when the blocks at the periphery are out of an image, said table having codewords, each codeword being determined based on a combination of the mode information of the target block and the mode information of the previously coded blocks at the periphery of the target block, or a combination of the mode information of the target block and temporary mode information as a substitute for the mode information of the blocks at the periphery of the target block when the blocks at the periphery are out of an image;
• and
• a block data coding section that is configured to code pixel data in the target block according to the mode information of the target block.

A computer-readable recording medium with an image coding program stored therein, said program being executed by a computer to code each block of a digital image divided into two-dimensional blocks, each block having a plurality of pixels, said program comprising:

• determining a coding mode for a target block to output mode information of the target block;
• outputting, as a codeword of the mode information of the target block, the codeword that is determined based on a combination of the mode information of the target block and the mode information of previously coded blocks at the periphery of the target block, or a combination of the mode information of the target block and temporary mode information as a substitute for the mode information of the blocks at the periphery of the target block when the blocks at the periphery are out of an image;
• and
• coding pixel data in the target block according to the mode information of the target block.