Method for Adaptively Screening a Continuous Tone Original and Device for Carrying Out Said Method

A process for screening the continuous-tone original to form its halftone copy by transformation of an input two-dimensional signal (Ei,k) of tone of an original, this signal comprising the multilevel tone values of an original areas (4) and presented in the matrix ([Ei,k]m,n) of m×n areas, into a two-dimensional signal (Ehftn i,k) of a halftone copy, this signal comprising the bi-level tone values of printing (6) and non-printing (5) elements and presented in the matrix ([Ehftn i,k]m,n) of m×n elements, the process comprising the steps of:

• forming the two-dimensional signals (Ewght 1,Ewght 2) of weight values distributions, these values belonging to the variety of said tone values and making up the weight value matrixes ([Ewght 1 i,k]m,n, [Ewght 2 i,k]m,n), which dimensionally correspond to matrixes of said areas and elements,
• distributing the values (Ewght 1) within the elements of the first of said weight matrixes without taking into account the tone variation over an original character and distributing the values (Ewght 2) within the second of said weight matrixes in dependence with contour or fine detail geometry on an original,
• forming the two-dimensional signal (Ehftn i,k) of a halftone copy, its bi-level values ascertained as result of comparison of the first ([Ewght 1 i,k]m,n) or of the second ([Ewght 2 i,k]m,n) weight matrixes with the matrix ([Ei,k]m,n) of tone values of an original,
• characterized in
• placing the part of weight values of said second matrix within the spatial intervals-segments, ascertaining the location of said segments by means of forming the contour trace (2) signal Etrace i,k as a matrix [Etrace i,k]m,n dimensionally corresponding to weight matrixes and comprising the informative, indicating the contour position, signal values for this matrix elements, corresponding to original areas containing a contour, and comprising the non-informative signal values for the rest elements of contour trace signal matrix,
• ascertaining the position of boundaries (1) of said segments dependant on the number of an adjacent elements used for the contour or fine detail reproduction on a halftone copy of an original.

A device for adaptive screening, comprising

• a source (9) of two-dimension spatially sampled tone signal of an original,
• a two-level halftone copy signal former (14) connected by its tone signal input (E) to said source output,
• a contour strength detector (10) connected by its input to said source output,
• a distributor (15) of the second weight values connected by its output to the second weight values input (Ewght 2) of the former and communicated by its output with the output of said detector, a distributor (13) of the first weight values connected by its output to the first weight values input (Ewght 1) of the former,
• characterized in that it contains additionally
• a contour trace two-dimensional signal generator (11) connected by its input to said detector output,
• a segments signal forming unit (12) connected by its input to said generator output and connected by its output to the second weight values distributor (15) and to the segments signal input (Esgm) of the former (14).