Patent ID: 7262885

Claim:
A halftone processor for converting a gray scale image comprising a plurality of in-bit pixels to a halftoned image comprising a plurality of n-bit pixel images, where m>n, the processor comprising: a memory storing a stochastic screen, the stochastic mask being a stochastic screen constrained by a checkerboard pattern, the checkerboard pattern constrained stochastic screen comprising a set of threshold values, each threshold value in the checkerboard pattern constrained stochastic screen corresponding to a gray level, each threshold value corresponding to a gray level between a first gray level (g s1 ) and a second gray level (g s2 ) being positioned in the checkerboard pattern constrained stochastic screen at a pixel position corresponding to a black pixel position in the checkerboard pattern, each threshold value corresponding to a gray level between the second gray level (g s2 ) and a third gray level (g s3 ) being positioned in the checkerboard pattern constrained stochastic screen at a pixel position corresponding to a white pixel position in the checkerboard pattern, the first gray level (g s1 ) being greater than the second gray level (g s2 ), the second gray level (g s2 ) being greater than the third gray level (g s3 ), the third gray level (g s3 ) corresponding to a black dither of 50% or less for gray levels (g s ) wherein x<g s <y, x corresponding to 100% black, y corresponding to 0% black; and a comparator receiving the gray scale image and the set of threshold values corresponding to the checkerboard pattern constrained stochastic screen, the comparator comparing, on a pixel-by-pixel basis, a value of each pixel in the gray scale image to a corresponding threshold value in the checkerboard pattern constrained stochastic screen to produce the halftoned image.