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Method for adaptively screening continuous tone originals

  • US 8,004,720 B2
  • Filed: 10/30/2006
  • Issued: 08/23/2011
  • Est. Priority Date: 10/31/2005
  • Status: Expired due to Fees
First Claim
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1. Method for adaptive screening a continuous tone original, presented by the multilevel sampling values of optical parameter (tone value) of its areas of relatively low spatial frequency, on a substrate, said method comprising:

  • dividing the copy substrate areas, corresponding to the areas of the original, into elements of relatively high spatial frequency;

    assigning each element of a substrate one of the first weight values, all normalized in accordance with a multilevel sampling scale and selected so as to achieve the desired smooth tone rendition;

    ascertaining the presence of detail on an original area corresponding to a given substrate area;

    with no detail being present in the original area, each element of said substrate area is formed dark if its first weight exceeds the optical parameter sampling value of said area of an original and is formed light if the first weight of said element doesn'"'"'t exceed the value of said area while;

    with the detail being present in said original area each element of the given copy area is assigned one of second weight values, all normalized in accordance with a multilevel sampling scale and selected so as to achieve accuracy of detail geometry reproduction;

    determining a first and a second supplementary tone value S1 and S2 for said detail-containing original area;

    forming each element of the corresponding copy area dark or light as result of comparison of a first weight of the element with a first supplementary tone value S1 and of the second weight of said element with a second supplementary tone value S2; and

    whereinthe presence of detail comprised of one or two boundaries dividing the given area on its darker and lighter parts is ascertained;

    with a detail being present by two boundaries, there is ascertained if the section located between said boundaries is darker or lighter than the outer to these boundaries part;

    in the event of the detail comprising one dividing boundary and the original area sampling tone value SE exceeding the predetermined threshold, or with the detail comprising two dividing boundaries and the section located between these boundaries being lighter of the outer part, the supplementary tone values are defined as
    S1=min(S)
    and
    S2=Smax(1−

    (max(S)−

    SE)/max(S)),where Smax is maximum possible tone value, max(S) is maximum value of an adjacent sampling areas, andeach element of the corresponding copy area is formed dark if its first weight exceeds the first supplementary tone value S1 and if its second weight exceeds the second supplementary tone value S2,otherwise the element is formed light;

    in the event of the detail comprising one dividing boundary and the original area sampling tone value SE isn'"'"'t exceeding the predetermined threshold, or with said detail comprising two boundaries and the section located between these boundaries being darker of the outer part, the supplementary tone values are defined as
    S1=min(S)
    and
    S2=Smax(SE

    min(S))/(Smax−

    min(S)),where min(S) is minimum value of tone values of an adjacent sampling areas, andeach element of the corresponding copy area is formed dark if its first weight exceeds the first supplementary tone value S1 or if its second weight exceeds the second the supplementary tone value S2,otherwise the element is formed light.

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