Image coding apparatus and method thereof and coded image decoding apparatus and method thereof

Abstract

In order to decrease a required memory capacity of a line memory and to efficiently compress an image by coding, even when character information is contained in a high-resolution image, each time the block of an image that is equally divided into M (M: an arbitrary integer greater than 1) blocks in the horizontal direction is updated, difference data between color code data at corresponding pixel positions in the horizontal line and the adjacent immediately-preceding horizontal line with respect to each horizontal line within the block is detected by a line memory and an exclusive-OR circuit. After a run has been detected from the difference data corresponding to the horizontal lines from the exclusive-OR circuit by a run end detecting circuit, when a coded word is run-length coded by a code creating and outputting circuit, a coded word corresponding to a first run is run-length coded in the state in which information of difference data of the run is contained in this coded word and coded words corresponding to runs other than the first run are run-length coded in the state in which transition type information, indicative of the type of transition of the difference data of the immediately-preceding run to the difference data of the run is contained in the coded words.