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Image processing apparatus and computer readable medium for implementing image processing

  • US 5,764,811 A
  • Filed: 06/04/1996
  • Issued: 06/09/1998
  • Est. Priority Date: 06/24/1993
  • Status: Expired due to Term
First Claim
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1. An image processing apparatus for converting multigradation image data into bigradation image data made from a first gradation value and a second gradation value, wherein said first gradation value<

  • said second gradation value, including;

    an error correction means outputting corrected pixel data (corrected by adding an error diffused from adjacent already binary-coded pixels to a target pixel multigradation image data);

    a threshold value setting means which sets a binary threshold value based on the gradation value of the multigradation image data of said target pixel; and

    a binary coding means, outputting said bigradation image data changed from said corrected pixel data based on the set threshold value;

    wherein with said target pixel multigradation image data gradation value (data), the median of said first gradation value and said second gradation value (m) and said threshold value (slsh), said threshold value setting means sets said binary coding threshold value slsh corresponding to said target pixel multigradation image data gradation value data, and satisfying at least one of the tolerance ranges shown in the following equations;

    in the case where the value of data is close to said first gradation value, data≦

    slsh≦

    (m+data)/2,in the case where the value of data is close to said second gradation value, (m+data)/2≦

    slsh≦

    data.

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