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Halftoning with enhanced dynamic range and edge enhanced error diffusion

  • US 5,268,774 A
  • Filed: 11/27/1991
  • Issued: 12/07/1993
  • Est. Priority Date: 11/27/1991
  • Status: Expired due to Term
First Claim
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1. A method of quantizing pixel values in an original image formed by a plurality of pixels, each pixel representing an optical density of the image at a location within the image, and having an original optical density value associated therewith selected from one of a set of c original optical density values that has a number of members larger than a desired output set of d optical density values, and having a dynamic range associated therewith, the steps comprising:

  • for each pixel, adding a previously determined error term to the original optical density value thereof, to derive a modified pixel value;

    determining for the pixel to be quantized, a threshold level that is a function of the original optical density of the pixel to be quantized, and a threshold value selected from a set of threshold values having a dynamic range that is greater than that of the original image;

    applying the determined threshold level to each optical density value of each pixel in the image, to produce an output optical density value that is a member of the desired output set, each member of the output set of d optical density values a legal output value;

    determining an error term that is a difference between the output optical density value and the modified optical density value of the modified pixel;

    applying a predetermined portion of the determined error term to the original optical density value of each of a predetermined set of pixels neighboring each pixel.

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