US7505177B2
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Method for generating a threshold value matrix for frequency modulated half-toning
Assignee: Heidelberger Druckmaschinen AG
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Filing: 2005-11-29
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Granted: 2009-03-17
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Expires: 2025-11-29
Abstract
Abstract A method for generating a threshold value matrix is used in the frequency-modulated half-toning of the image data to be reproduced. A threshold value matrix for a basic screen is generated in that low-pass filters of different width are applied to the bit patterns generated and the threshold value distribution is changed on the basis of the filtered results. Furthermore, the bit patterns generated are examined for specific part patterns and the threshold value distribution is changed in such a way that undesired part patterns no longer occur and, instead, desired part patterns, preferably rounded forms, are contained in the bit patterns generated. By use of a combination of scaling and/or rotation and/or mirroring of the threshold value matrix of the basic screen, threshold value matrices are generated for the printing inks.
Inventors
- 👤 Jörg Olaf von Wechgeln
- 👤 Michael Hansen
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 22:57
CPC Classifications
H; H04; H04N; H04N1/00; H04N1/40; H04N1/405; H04N1/4051
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
236 words
A method for generating a threshold value matrix for a basic screen for frequency-modulated half-toning for generating a half-toned form of image data, which comprises the steps of: varying the image data in a total value range between 0% and 100%; forming the threshold value matrix to contain MX×MY threshold values and being filled with the threshold values from 0 to (MX×MY−1); determining values of image points of the half-toned form by performing a comparison between tonal values of the image data and the threshold values of the threshold value matrix; placing black points alternately in a first binary data field having MX×MY binary points; placing white points in a second binary data field having MX×MY binary points; determining first positions with at least two low-pass filters of different width applied to the first binary data field and to the second binary data field respectively; at the first positions or in an environment of the first positions, performing a search for specific part patterns of the black or white points and second positions are determined there, at which the black and white points are respectively placed; and at the second positions of the black points, entering the threshold values from 0 to ((MX×MY)/2−1) in the threshold value matrix in ascending order and at the second positions of the white points, entering the threshold values from (MX×MY−1) to ((MX×MY)/2) in the threshold value matrix in descending order.
Claim 2
Independent Claim
236 words
A method for generating a threshold value matrix for a basic screen for frequency-modulated half-toning for generating a half-toned form of image data, which comprises the steps of: varying the image data in a total value range between 0% and 100%; forming the threshold value matrix to contain MX×MY threshold values and being filled with the threshold values from 0 to (MX×MY−1); determining values of image points of the half-toned form by performing a comparison between tonal values of the image data and the threshold values of the threshold value matrix; placing black points alternately in a first binary data field having MX×MY binary points; placing white points in a second binary data field having MX×MY binary points; determining first positions with at least two low-pass filters of different width applied to the first binary data field and to the second binary data field respectively; at the first positions or in an environment of the first positions, performing a search for specific part patterns of the black or white points and second positions are determined there, at which the black and white points are respectively placed; and at the second positions of the black points, entering the threshold values from 0 to ((MX×MY)/2−1) in the threshold value matrix in ascending order and at the second positions of the white points, entering the threshold values from (MX×MY−1) to ((MX×MY)/2) in the threshold value matrix in descending order.
Claim 3
Dependent Claim
37 words
The method according to claim 1 , which further comprises generating further threshold value matrices for printing inks by performing a combination of scaling and/or rotation and/or mirroring of the threshold value matrix of the basic screen.
Claim 4
Dependent Claim
18 words
The method according to claim 2 , which further comprises setting rotation amounts to a multiple of 90°.
Claim 5
Dependent Claim
159 words
The method according to claim 1 , which further comprises optimizing the threshold value matrix by the further steps of: in a binary data field having a bit pattern of the black and white points produced when the threshold values are compared with a predefined tonal value, using at least two low-pass filters of different widths, which are applied to the binary data field, for determining a position of a maximum filtered value and a position of a minimum filtered value; at the position of the maximum filtered value and the minimum filtered value or in an environment of these positions, performing a search for specific part patterns of the black and white points and modified positions of the maximum filtered value and the minimum filtered value are determined there; interchanging, at the modified positions in the binary data field, the black and white points; and interchanging, at the modified positions in the threshold value matrix, the threshold values.
Claim 6
Dependent Claim
35 words
The method according to claim 4 , wherein as a result of the interchanging of the black and white points, part patterns having pointed and angular structures are converted into part patterns having round structures.
Claim 7
Dependent Claim
96 words
The method according to claim 1 , which further comprising optimizing the threshold value matrix by the further steps of: in a binary data field having a bit pattern of black and white points produced when the threshold values are compared with a predefined tonal value, performing a search for specific part patterns of the black and white points and determining the positions of the part patterns; interchanging, at the positions found in the binary data field, the black and white points; and interchanging, at the positions found in the threshold value matrix, the threshold values.
Claim 8
Dependent Claim
24 words
The method according to claim 6 , wherein as a result of the interchanging of the black and white points, isolated points are eliminated.
Claim 9
Dependent Claim
84 words
The method according to claim 1 , which further comprises assessing a quality of the threshold value matrix by the further steps of: in binary data fields having bit patterns of the black and white points produced when the threshold values are compared with different tonal values, determining a maximum filtered value and a minimum filtered value by using at least one low-pass filter; and using a difference between the maximum filtered value and the minimum filtered value as a measure of the quality.
Claim 10
Dependent Claim
78 words
The method according to claim 1 , which further comprises assessing a quality of a threshold value matrix by the further steps of: in binary data fields having bit patterns of the black and white points produced when the threshold values are compared with different tonal values, performing a search for specific part patterns, to which weights are assigned in groups; and using a sum of the weights of the part patterns as a measure of the quality.
References Cited (Backward Citations)
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