Patent ID: RE42473

Claim:
A method of generating a halftone image from an input digital image, said input digital image represented by a multiplicity of pixels, each pixel having a given value, said values being stored in a memory, said method comprising the steps of : (A) determining the one or more properties including local properties of the input digital image; (B) filtering the input digital image, said filtering having as output a filtered value at each pixel; (C) obtaining the difference between the value at the a pixel and the filtered value at the pixel, said difference being a threshold input; (D) generating the an output state for the pixel depending upon the relationship of the value of said threshold input relative to a threshold; (E) producing an error value, said error value being indicative of the deviation of said threshold input from the output state; (F) multiplying said error value by a coefficient, the result of said multiplication being stored; (G) combining the stored value with the difference between the next pixel value and the next filtered value to produce a new threshold input; (H) repeating steps (D) through (G) the generating an output state, the producing an error value, the multiplying said error value, and the combining the stored error value for each pixel in the input digital image thereby producing a halftone image; and varying the threshold according to the one or more properties of the input digital image; and selectively changing the coefficient in step (E) according to the local one or more properties of the input digital image.