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Method and apparatus for determining halftone line frequency estimates using MIN/MAX detection

  • US 6,734,991 B1
  • Filed: 09/24/1999
  • Issued: 05/11/2004
  • Est. Priority Date: 09/24/1999
  • Status: Expired due to Fees
First Claim
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1. A method of determining a halftone line frequency estimate f at each pixel V(i) of an image formed of a plurality of pixels arranged in a plurality of fastscan pixel rows and slowscan pixel columns, the method comprising the steps of:

  • for each fastscan pixel row of said image;

    identifying a set of fastscan maxima extrema pixels having a video value greater than selected neighboring fastscan direction pixels; and

    , identifying a set of fastscan minima extrema pixels having a video value less than selected neighboring fastscan direction pixels;

    for each slowscan pixel column of said image;

    identifying a set of slowscan maxima extrema pixels having a video value greater than selected neighboring slowscan direction pixels; and

    , identifying a set of slowscan minima extrema pixels having a video value less than selected neighboring slowscan direction pixels;

    for each pixel of said image;

    generating a fastscan maxima extrema frequency value fHx based on a quantity of neighboring of fastscan maxima extrema pixels;

    generating a fastscan minima extrema frequency value fHn based on a quantity of neighboring fastscan minima extrema pixels;

    generating a slowscan maxima extrema frequency value fVx based on a quantity of neighboring slowscan maxima extrema pixels; and

    , generating a slowscan minima extrema frequency value fVN based on a quantity of neighboring slowscan minima extrema pixels;

    for each pixel of said image;

    generating a halftone fastscan frequency estimate fH by selecting the greater between the fastscan maxima extrema frequency value fHx at said each pixel and the fastscan minima extrema frequency value fHn at said each pixel; and

    , generating a halftone slowscan frequency estimate fV by selecting the lesser between the slowscan maxima extrema frequency value fVx at said each pixel and the slowscan minima extrema frequency value fVn at said each pixel; and

    , for each pixel, determining a halftone line frequency estimate f based on a norm of said halftone fastscan frequency estimate fH and said halftone slowscan frequency estimate fV.

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