| 摘要 |
PURPOSE:To improve data compressibility, to encode a source image with high fidelity and further to execute encoding while suppressing the change of picture quality such as gradation, etc., in the source image at a minimum. CONSTITUTION:A preprocessing part 11 transforms source image data into a character string expressing a pattern PN and a run length RL and inputs the character string to an LZW encoding part 12a, and the LZW encoding part 12a retrieves a character string coincident with the longest by collating the characters of the character string with a character string registered on a dictionary part 12b one by one from the head character. When the character string containing the character coincident with the input character does not exists in the dictionary part 12b in the case of retrieving this longest coincident character string, an approximate character approximate to the input character is calculated from an approximate character generation part 12c and when the registered character string containing the approximate character is existent, the longest coincident character string is continuously retrieved by using the approximate character string containing the approximate character. Then, the input character string is encoded according to the retrieved longest coincident character string and registered on the dictionary part 12b while applying a number to the character string adding the next input character to the longest coincident character string. |
