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Multi-level halftoning providing improved texture uniformity

  • US 20050195438A1
  • Filed: 03/05/2004
  • Published: 09/08/2005
  • Est. Priority Date: 03/05/2004
  • Status: Active Grant
First Claim
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1. A method for multi-level halftoning an input digital image having input pixels with corresponding input pixel values and Ni input levels to form an output digital image having output pixels with corresponding output pixel values and No output levels, where 2≦

  • No

    Ni, comprising;

    a) determining a periodic dither signal by modularly addressing a dither signal array with the row and column address of an input pixel in the input digital image, wherein the dither signal array is designed to produce periodic dither signals having low visibility to a human observer;

    b) adjusting the amplitude of the periodic dither signal in response to the input pixel value of the input pixel wherein the amplitude adjustment is a function of the texture characteristics that would result from the application of a multi-level error diffusion halftoning process to a uniform image region having the particular input pixel value, the amplitude of the adjusted periodic dither signal being larger for input pixel values that would produce visually objectionable texture characteristics than for input pixel values that would produce visually pleasing texture characteristics;

    c) combining the adjusted periodic dither signal with the input pixel value to produce an adjusted pixel value;

    d) applying the multi-level error diffusion halftoning process to the adjusted pixel value to determine the output pixel value; and

    e) repeating steps a)-d) for multiple input pixels of the input digital image to thereby provide the output digital image.

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