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Image processor with smooth transitioning between dither and diffusion processes

  • US 5,014,333 A
  • Filed: 07/21/1988
  • Issued: 05/07/1991
  • Est. Priority Date: 07/21/1988
  • Status: Expired due to Fees
First Claim
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1. An image processor comprising:

  • image memory means for storing an image comprising a frame of M columns and N rows of multi-gray level pixels;

    adder means for forming successive input amplitudes from successive ones of said pixel so as to form a current input amplitude corresponding to the current one of said pixels;

    means for comparing said current input amplitude with a dithered threshold so as to generate;

    a. a binary print/no print decision,b. a feedback error;

    means for attenuating said feedback error so as to produce an attenuated error, said attenuating means responsive to the average gray level of a local neighborhood of pixels surrounding said current pixel so as to attenuate said feedback error proportionately as said average gray level approaches a light or dark limit;

    means for transmitting said attenuated error to said adder means so that said adder means adds said attenuated error to the next one of said successive pixels to form the next one of said successive input amplitudes; and

    means for transmitting said dithered threshold to said comparator means, comprising;

    a. means for storing a plurality of ordered dither matrices, each of said matrices defining plural patterns of dithered thresholds as individual elements in each of said matrices, each of said patterns characterized by dither threshold amplitudes for each of said M ×

    N pixels spatially modulated with a contour of a characteristic sharpness,b. means for sensing the amplitude of the high spatial frequency content of said local neighborhood,c. means for selecting one of said plurality of ordered dither matrices whereby the characteristic sharpness of the one ordered dither matrix so selected is inversely proportional to the amplitude of the high spatial frequency content of said local neighborhood, andd. means for selecting for said dithered threshold an element within the one selected ordered dither matrix corresponding to the position of the current one of said successive pixels stored in said image storing means, whereby an ordered dither process is provided which is attenuated in proportion to the amplitude of the high spatial frequency content of the local neighborhood surrounding each successive one of said M ×

    N pixels.

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