Down-scaling technique for bi-level images

Abstract

In a preferred method for horizontal down-scaling of a pixel pattern, the down-scaling is performed on a byte-by-byte basis along each row of pixels. To avoid loss of information, if a pixel to be deleted is black and the black pixel has two original white immediate neighbors, the pixel to the right of the black pixel to be deleted is set to black. Each byte may be processed independently from the other bytes. In a preferred method for vertical down-scaling of a pixel pattern, a pixel row to be deleted, to achieve the desired down-scaling, is identified. To avoid loss of information, pixels in a byte of pixels in the row to be deleted are bit-wise logically OR'd with the corresponding pixels in the next row, and the OR'd values replace the pixels in that next row. Changing the pixel values during the horizontal or vertical down-scaling is only performed if it is determined that the byte is part of text and not part of a picture. In the preferred embodiment circuit, look-up tables are used which receive the original bytes as addresses and output the horizontally down-scaled pixels. A look-up table may also determine if the byte is part of text or part of a picture. The total memory capacity required for the circuit is small compared to the prior art, and the processing is fast.