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Methods and apparatus for providing digital halftone images with random error diffusion dithering

  • US 5,835,687 A
  • Filed: 10/21/1996
  • Issued: 11/10/1998
  • Est. Priority Date: 10/21/1996
  • Status: Expired due to Fees
First Claim
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1. A process for performing error diffusion to print an image with reduced visually apparent artifacts, wherein the process is performed by a processor connected to a scanner that scans the image and detect intensity values at selected pixel locations, the process comprising the steps of:

  • encoding selected ones of the pixel locations as binary values, and calculating error values corresponding to differences between modified intensity values for such pixel locations and predetermined threshold values;

    for selected pixel neighbors of an ith pixel location in the scanned image, diffusing the calculated error value, Ei, of the ith pixel location to its selected neighbors as follows;

    
    
    space="preserve" listing-type="equation">e.sub.j =w.sub.j *E.sub.iwhere ej is the error value diffused to the jth pixel neighbor from the ith pixel location, where the jth pixel neighbor is a second-adjacent pixel location to the right of the ith pixel location and on the same scan line as the ith pixel location, and where wj is a weighting factor randomly selected for the jth pixel location from a predetermined ordered set of weighting factors;

    continuing the error diffusion process for other pixel neighbors of the ith pixel location, wherein the other pixel neighbors are located on a scan line following the scan line of the ith pixel location and are adjacent or diagonally-adjacent to the ith or jth pixel location, and wherein the weighting factors applied to the other pixel neighbors are selected from the ordered set of weighting factors in accordance with the weighting factor selected for the jth pixel location; and

    continuing the error diffusion process for the (i+1)th pixel location and so forth, such that coding errors are diffused from substantially all of the pixel locations in the image.

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