From given code data, a first total data amount of codes is calculated for each processing unit. A second total data amount of codes is calculated for each processing unit from the first data amount of codes for each processing unit, which second data amount is a data amount obtained when image data obtained from decoding the code data is again compressed and coded at a higher compression rate. A re-compressed code data is obtained from updating the additional information to information for the re-compressed state, and reading the data of codes for each processing unit from a memory for the second total data amount in a predetermined manner.