METHOD FOR COMPRESSION ENCODING AND DECODING OF BITMAP FONT, PROGRAM, AND DATA STRUCTURE OF COMPRESSION-ENCODED DATA

摘要

PROBLEM TO BE SOLVED: To improve a compression rate of compression-encoded data of a bitmap font and decode the bitmap font from the compression-encoded data line by line.

SOLUTION: A bitmap font constructed with X dots in a horizontal direction and Y dots in a vertical direction is segmented into sub-blocks each constructed with 4 dots in the horizontal direction and 1 dot in the vertical direction. A dot value of the sub-block constituting a background of a character is run length encoded. Regarding the sub-block not constituting a background of a character but satisfying any one of four kinds of conditions, it is encoded using a condition code representing the kind of the condition and a prediction error with respect to 2 dots not required to have a background color in the condition. Regarding the sub-block not satisfying any of the four kinds of conditions, it is encoded using a prediction error with respect to 4 dots.

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