Removal of error diffusion artifacts with alternating distribution weights

An image processing system for converting a continuous-tone image represented by a plurality of electronically encoded pixels, each having a color value, stored in an input buffer into an encoded image for electronic printing, comprising

• a buffer controller for sequentially selecting one of said pixels stored in said input buffer,
• a first summing circuit receiving the color value of said selected pixel and modifying said color value based on a fractional error value obtained from a previously processed pixel to obtain a modified color value,
• an image register receiving said modified color value and temporarily storing said modified value,
• a comparator receiving said modified value from said image register and comparing said modified value with a selected threshold to choose one of a plurality of output states based on said comparison, said selected output state representing said selected pixel in the encoded image,
• a change sign inverter receiving said selected output state and producing a sign-inverted output state,
• a second summing circuit receiving said modified color value and said sign-inverted output state to produce an error value indicative of a difference between said modified color value and said output state,
• a modifier receiving said error value from said summing circuit and receiving a weighted fraction from a look-up table and modifying said error value based on said weighted fraction to obtain a fractional error value to be applied to a subsequent pixel, said weighted fraction being selected based on the color value of said selected pixel and its position within said electronically encoded image, and
• an error buffer for storing said fractional error value.

A method for converting a continuous-tone represented as a two-dimensional array of electronically encoded pixels each specifying a gray scale value into an encoded display image for electronic printing, comprising the steps of

• segmenting the two-dimensional array of electronically encoded pixels into a plurality of regions,
• comparing the gray scale value of a selected pixel with a selected threshold,
• selecting an output state from a set of binary states for displaying said pixel based on the comparison of the gray scale value with the selected threshold,
• obtaining an error value indicative of a difference between said selected output state and said gray scale value of the pixel,
• dividing said error value into a plurality of fractional error values based on which segment said selected pixel is located within said segmented two-dimensional array and based on the gray scale intensity of said pixel,
• adding to each of a selected plurality of subsequent pixels one of said fractional error values based on a relative position of said subsequent pixel to said selected pixel,
• repeating the above steps for each pixel in said array to produce an encoded display image.