Method for Adaptively Screening Continuous Tone Originals
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Abstract
The invention relates to printing, to facsimile and publishing techniques, in particular to picture reproducing systems capable to form two optical parameter levels, only. Said invention makes it possible to increase a fine detail reproduction accuracy, in particular, strokes on a screen copy and to more fully use a printing resolution power. The inventive method consists in converting a continuous tone original represented by multilevel reflection values of the areas thereof into a screen copy consisting of dark and light elements by using two types of weight values of the copy elements, wherein the first weight values are distributed between the elements in a sequence independent of the tone modification behavior through the original areas, and in the second sequence according to the geometry of the fine details thereof, in forming the copy elements in such a way that they are dark or light according to results of comparison between the reflection values of the original areas and the weight values of the first and second types, in increasing the degree of use of the second weight values for the fine strokes of the original with respect to the use thereof for single interfaces, which divide the original into dark and light regions and in removing elements which are established in a dark form according to the first weight values inside the light strokes arranged on a dark background.
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Citations
8 Claims
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1-4. -4. (canceled)
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5. 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 comprising the steps of
dividing the copy substrate areas, corresponding to the areas (A, B, C, D, E, F, G, F, H, I) of the original, into elements of relatively high spatial frequency, assigning each element of a substrate areas one of the first weight values (P1), 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 (1) on original area (E) corresponding to given substrate area, with no detail (1) being present in original area (E), each element of said substrate area is formed dark if its first weight (P1) exceeds the optical parameter sampling value SE of said area (E) of an original and is formed light if the first weight (P1) of said element doesn'"'"'t exceed the value SE of said area (E) while, with detail (1) being present in said original area (E) each element of the given copy area is assigned one of the second weight values (P2), all normalized in accordance with a multilevel sampling scale and selected so as to achieve the desired accuracy of detail geometry reproduction, determining a first and a second supplementary tone values S1 and S2 for said detail-containing original area, forming an each element of the corresponding copy area dark or light as result of comparison of a first weight (P1) of the element with a first supplementary tone value S1 and of the second weight (P2) of said element with a second supplementary tone value S2, and characterized in that the 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 and, in the event of the detail comprising one dividing boundary and the original area (E) 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=max(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, and each element of the corresponding copy area is formed dark if its first weight (P1) exceeds the first supplementary tone value S1 and if its second weight (P2) exceeds the second supplementary tone value S2, otherwise the element is formed light while, in the event of the detail comprising one dividing boundary and the original area (E) 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, and each element of the corresponding copy area is formed dark if its first weight (P1) exceeds the first supplementary tone value S1 or if its second weight (P2) exceeds the second the supplementary tone value S2, otherwise the element is formed light. - View Dependent Claims (6, 7, 8)
- (max(S)−
Specification