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Adaptive filtering and thresholding arrangement for reducing graininess of images

  • US 5,757,976 A
  • Filed: 08/08/1996
  • Issued: 05/26/1998
  • Est. Priority Date: 10/11/1994
  • Status: Expired due to Fees
First Claim
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1. A method for improving the quality of a halftone image generated from an input stream of continuous-tone image pixels, the method comprising the steps of:

  • determining a grayscale value for a selected one of the pixels of the input stream;

    adaptively quantizing said gray scale value of the selected pixel to generate a quantization error;

    providing;

    a first error filter corresponding to a first range of quantized grayscale values and having a first size and a first weighting coefficient, anda second error filter corresponding to a second range of quantized grayscale values and having a second size and a second weighting coefficient; and

    selecting one of;

    the first error filter when the quantized grayscale value of the selected pixel is within the first range, andthe second error filter when the quantized grayscale value of the selected pixel is within the second range,wherein said selected error filter is configured to diffuse said quantization error among neighboring pixels of said input stream in a manner that improves the quality of said halftone image.

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