EP0673150A2
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Method and apparatus for generating halftone image
Assignee: Dainippon Screen Manufacturing Co Ltd
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Filing: 1995-03-15
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Granted: —
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Expires: 2015-03-15
Abstract
Abstract The present invention is to generate a binary halftone image by taking full advantage of high resolution dots and low resolution dots. A Laplacian filter is applied to the density data of an original image to determine filtered density data representing spatial frequencies of the original image. A dot selection signal (SEL) for selecting one of the high resolution dots and the low resolution dots is generated based on a comparison between the filtered density data and a threshold data. A dot generator (32) includes a first screen pattern memory (48) for storing a threshold pattern of the low resolution dots and a second screen pattern memory (50) for storing a threshold pattern of the high resolution dots. A selector (52) receives threshold data DTH1 and DTH2 output from the first and the second memory (48) and (50) and selects one of the threshold data DTH1 and DTH2 in response to the dot selection signal (SEL). A comparator (54) compares image data D IM with the selected threshold data and generates a dot signal Sd to record a binary halftone image.
Inventors
- 👤 Katsuhiko C/O Dainippon Screen Mfg. Co. Furusawa
- 👤 Shoichi C/O Dainippon Screen Mfg.Co. Ltd Shimada
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-09 17:10
CPC Classifications
H; H04; H04N; H04N1/00; H04N1/40; H04N1/405
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
80 words
A method of generating a binary halftone image based on image data representing an original image, said method comprising the steps of: (a) measuring spatial frequencies in said original image; and (b) generating said binary halftone image by producing high resolution dots in a first image region and low resolution dots in a second image region, said first image region having spatial frequencies higher than a threshold frequency, said second image region having spatial frequencies lower than said threshold frequency.
Claim 2
Dependent Claim
120 words
A method in accordance with claim 1, wherein said step (a) comprises the steps of: (c) obtaining density data indicative of a density of each pixel in said original image from said image data of said original image; and (d) applying a second differential filter to said density data to thereby generate filtered density data indicative of a spatial frequency in the proximity of each pixel in said original image; and said step (b) comprises the steps of: (e) comparing said filtered density data with said threshold frequency to thereby generate a selection signal for each pixel; and (f) selecting one of said high resolution dots and said low resolution dots to each pixel in response to said selection signal.
Claim 3
Dependent Claim
38 words
A method in accordance with claim 2, wherein said step (f) comprises the step of: (g) dividing said original image into said first image region and said second image region based on a distribution of said selection signal.
Claim 4
Dependent Claim
70 words
A method in accordance with claim 3, wherein said step (g) comprises the steps of: dividing said original image into a plurality of unit areas of an identical size; and obtaining a logical sum of said selection signal for a plurality of pixels in each of said plurality of unit areas, to thereby identifying each of said plurality of unit area as one of said first and second image regions.
Claim 5
Dependent Claim
62 words
A method in accordance with claim 3, wherein said step (g) comprises the steps of: displaying a binary image representing said distribution of said selection signal in said original image on a display device; and dividing said original image into said first image region and said second image region through interactive operation while observing said binary image displayed on said display device.
Claim 6
Dependent Claim
59 words
A method in accordance with claim 3, wherein said step (g) comprises the steps of: displaying a multi-valued image representing a distribution of said filtered density data on a display device; and dividing said original image into said first image region and said second image region through interactive operation while observing said multi-valued image displayed on said display device.
Claim 7
Dependent Claim
220 words
A method in accordance with claim 1, wherein said step (a) comprises the steps of: providing a first threshold pattern for said high resolution dots and a second threshold pattern for said low resolution dots; obtaining density data indicative of a density of each pixel in said original image from said image data of said original image; applying a second differential filter to said density data to thereby generate filtered density data indicative of a spatial frequency in the proximity of each pixel in said original image; and determining a first coefficient for said high resolution dots and a second coefficient for said low resolution dots from said filtered density data of each pixel; and said step (b) comprises the steps of: reading out a first threshold value from said first threshold pattern and a second threshold value from said second threshold pattern with respect to each pixel in said original image; multiplying said first threshold value by said first coefficient and said second threshold value by said second coefficient, and generating a third threshold value by adding the results of multiplication; comparing said image data with said third threshold with respect to each pixel in said original image, to thereby generate a dot signal representing said binary halftone image; and generating said binary halftone image from said dot signal.
Claim 8
Dependent Claim
22 words
A method in accordance with claim 1, wherein said high resolution dots are frequency modulation dots whose spacing varies with image density.
Claim 9
Independent Claim
81 words
An apparatus for generating a binary halftone image based on image data representing an original image, comprising: frequency measuring means for measuring spatial frequencies in said original image; and dot generation means for generating said binary halftone image by producing high resolution dots in a first image region and low resolution dots in a second image region, said first image region having spatial frequencies higher than a threshold frequency, said second image region having spatial frequencies lower than said threshold frequency.
Claim 10
Dependent Claim
121 words
An apparatus in accordance with claim 9, wherein said frequency measuring means comprises: means for obtaining density data indicative of a density of each pixel in said original image from said image data of said original image; and means for applying a second differential filter to said density data to thereby generate filtered density data indicative of a spatial frequency in the proximity of each pixel in said original image; and said dot generation means comprises: means for comparing said filtered density data with said threshold frequency to thereby generate a selection signal for each pixel; and selection means for selecting one of said high resolution dots and said low resolution dots to each pixel in response to said selection signal.
Claim 11
Dependent Claim
37 words
An apparatus in accordance with claim 10, wherein said selection means comprises: division means for dividing said original image into said first image region and said second image region based on a distribution of said selection signal.
Claim 12
Dependent Claim
71 words
An apparatus in accordance with claim 11, wherein said division means comprises: means for dividing said original image into a plurality of unit areas of an identical size; and means for obtaining a logical sum of said selection signal for a plurality of pixels in each of said plurality of unit areas, to thereby identifying each of said plurality of unit area as one of said first and second image regions.
Claim 13
Dependent Claim
65 words
An apparatus in accordance with claim 11, further comprising: a display device for displaying a binary image representing said distribution of said selection signal in said original image; and wherein said division means comprises: means for specifying to divide said original image into said first image region and said second image region through interactive operation while observing said binary image displayed on said display device.
Claim 14
Dependent Claim
65 words
An apparatus in accordance with claim 11, further comprising: a display device for displaying a binary image representing said distribution of said selection signal in said original image; and wherein said division means comprises: means for specifying to divide said original image into said first image region and said second image region through interactive operation while observing said multi-valued image displayed on said display device.
Claim 15
Dependent Claim
245 words
An apparatus in accordance with claim 9, further comprising: a first threshold memory for storing a first threshold pattern for said high resolution dots; and a second threshold memory for storing a second threshold pattern for said low resolution dots; and wherein said frequency measuring means comprises: means for obtaining density data indicative of a density of each pixel in said original image from said image data of said original image; means for applying a second differential filter to said density data to thereby generate filtered density data indicative of a spatial frequency in the proximity of each pixel in said original image; and means for determining a first coefficient for said high resolution dots and a second coefficient for said low resolution dots from said filtered density data of each pixel; and said dot generation means comprises: means for reading out a first threshold value from said first threshold memory and a second threshold value from said second threshold memory with respect to each pixel in said original image; means for multiplying said first threshold value by said first coefficient and said second threshold value by said second coefficient, and generating a third threshold value by adding the results of multiplication; a comparator for comparing said image data with said third threshold with respect to each pixel in said original image, to thereby generate a dot signal representing said binary halftone image; and means for generating said binary halftone image from said dot signal.
Claim 16
Dependent Claim
22 words
An apparatus in accordance with claim 9, wherein said high resolution dots are frequency modulation dots whose spacing varies with image density.
References Cited (Backward Citations)
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