System and method for irreversible data compression of bit map images

摘要

PURPOSE: To obtain a uniform image quality through the whole of an image by irreversibly compressing bit map image data divided into blocks at every block and again expanding this compression data and preventing the occurrence of the difference of image quality due to the blocks in an expanded image. ;CONSTITUTION: When one block of blocked image data is received from a host computer, a printer divides the position coordinates X, Y on printing paper of the head pixel of the block by the number 4 of pixels of one side of a cell (e.g. 4×4 pixels) being an irreversible compression unit to set the surpluses RX, RY to the horizontal and vertical offsets related to a block B. Next, the address obtained by subtracting the offsets RX, RY from the address ADD of the leading end of the block is set to the head address of the first cell and the cell is taken out of the block. The dot pattern of each cell is converted to a compression code. That is, the cell is divided on the basis of the position on printing paper and each cell is irreversibly compressed.;COPYRIGHT: (C)1996,JPO