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

摘要

A method for reducing the line memory capacity and effectively encoding/compressing a high-resolution image, even when character information is contained in the image is disclosed. For every block update for an image divided into identical M (M is an integer not smaller than 1) blocks in the horizontal direction, for each of the horizontal lines in the blocks, a line memory 41 and an exclusive OR circuit 42 successively detect a difference between colour codes at corresponding pixel positions in a horizontal line and the adjacent preceding horizontal line. Moreover, a run end detection circuit 43 detects a run from the difference corresponding to the horizontal line from the exclusive ORcircuit 42. When a code creation/output circuit 44 encodes the run length, the code word for the first run includes information on the difference in the run while the code word for runs other than the first run includes, instead of the difference information in the run, transition type information indicating the type of transition to the difference in the run of the difference in the preceding run, thereby performing run length encoding.