A New Code for Transmission of Ordered Dithered Pictures

Dithering is an image processing technique that creates a two-level picture that gives the illusion of a multilevel picture by appropriately arranging the spatial density of the two levels (usually black and white) on the picture.1"5 The dithering technique consists of comparing a multilevel image with a position-dependent threshold and setting pels to white when the input signal exceeds the threshold. Other pels are set to black. The matrix of threshold values (called the dither matrix) is repeated over the entire picture to provide the threshold pattern for the whole image. The merit of a dither matrix is judged from the quality of its rendition of the original picture. A class of dither matrices of special interest is the ordered dither matrices, 3 which use a simple recursion algorithm to create dither matrices of size 2" X 2n to simulate 22" + 1 brightness levels. 379 In the case of the 4 x 4 matrix, the 16 threshold levels are put in the following positions: 0 8 2 12 4 14 3 11 1 15 7 13 10 6 9 5