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US5060284A
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Adaptive error diffusion thresholding for document images
Assignee: Eastman Kodak Co
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Filing: 1990-03-23
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Granted: 1991-10-22
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Expires: 2010-03-23
Abstract
Abstract Apparatus for converting multilevel video images into a bilevel image having an accurate rendition of the original grayscale of the image. The apparatus can provide an improved rendition of low contrast images.
Inventors
- 👤 Kevin J. Klees
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-04 21:53
CPC Classifications
H; H04; H04N; H04N1/00; H04N1/40; H04N1/405; H04N1/4051; H04N1/4052; G; G06; G06V; G06V10/00; G06V10/20; G06V10/28
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
232 words
Apparatus for performing error diffusion thresholding of multiple level digital images into bi-level digital images using either a local minimum or local maximum signal to calculate the error signal, said apparatus comprising: means for scanning a grayscale image and detecting the density levels of individual input pixels; means for delaying said input pixels by a predetermined number of pixel locations per line and by a predetermined number of scan lines; means for generating a fixed threshold signal; means for comparing said threshold signal to one of said delayed pixels to generate a bi-level output pixel value; means for generating a signal representing the local minimum signal level of said input pixels; means for generating a signal representing the local maximum signal level of said input pixels; means for selecting either the said local minimum or said local maximum based on said output pixel; means for generating an error signal using said selected minimum or maximum signal and the said delayed pixel used in said thresholding comparison, such that said error signal contains either positive or negative sign information; means for weighting said error signal by a fixed number of predetermined factors; means for adding or subtracting said weighted error signal from said fixed number of remaining delayed pixel values thus generating new delayed pixel values; and means for checking to insure that said new delayed pixel values are within a predetermined range.
Claim 2
Dependent Claim
232 words
Apparatus for performing error diffusion thresholding of multiple level digital images into bi-level digital images using either a local minimum or local maximum signal to calculate the error signal, said apparatus comprising: means for scanning a grayscale image and detecting the density levels of individual input pixels; means for delaying said input pixels by a predetermined number of pixel locations per line and by a predetermined number of scan lines; means for generating a fixed threshold signal; means for comparing said threshold signal to one of said delayed pixels to generate a bi-level output pixel value; means for generating a signal representing the local minimum signal level of said input pixels; means for generating a signal representing the local maximum signal level of said input pixels; means for selecting either the said local minimum or said local maximum based on said output pixel; means for generating an error signal using said selected minimum or maximum signal and the said delayed pixel used in said thresholding comparison, such that said error signal contains either positive or negative sign information; means for weighting said error signal by a fixed number of predetermined factors; means for adding or subtracting said weighted error signal from said fixed number of remaining delayed pixel values thus generating new delayed pixel values; and means for checking to insure that said new delayed pixel values are within a predetermined range.
Claim 3
Dependent Claim
16 words
The apparatus in claim 1 wherein said local maximum signal is generated by a peak detector.
Claim 4
Dependent Claim
16 words
The apparatus in claim 1 wherein said local minimum signal is generated by a valley detector.
Claim 5
Dependent Claim
26 words
The apparatus in claim 1 wherein said selection of local minimum or maximum values is a two to one multiplexer controlled by the bi-level output pixel.
Claim 6
Dependent Claim
20 words
The apparatus in claim 1 wherein said delaying means further comprises: a line delaying means and a pixel delaying means.
Claim 7
Dependent Claim
222 words
Apparatus for performing error diffusion thresholding of multiple level digital images into digital images with fewer levels using either a local minimum or local maximum signal to calculate the error signal, said apparatus comprising: means for scanning a grayscale image and detecting the density levels of individual input pixels; means for delaying said input pixels by a predetermined number of pixel locations per line and by a predetermined number of scan lines; means for generating an output pixel value using one of said delayed pixels; means for generating a signal representing the local minimum signal level of said input pixels; means for generating a signal representing the local maximum signal level of said input pixels; means for selecting either the said local minimum or said local maximum based on said output pixel; means for generating an error signal using said selected minimum or maximum signal and the said delayed pixel used in said thresholding comparison, such that said error signal may contain either positive or negative signal information; means for weighting said error signal using a fixed number of predetermined factors; means for adding or subtracting said weighted error signal from said fixed number of remaining delayed pixel values thus generating new delayed pixel values; and means for checking to insure that said new delayed pixel values are within a predetermined range.
Claim 8
Dependent Claim
222 words
Apparatus for performing error diffusion thresholding of multiple level digital images into digital images with fewer levels using either a local minimum or local maximum signal to calculate the error signal, said apparatus comprising: means for scanning a grayscale image and detecting the density levels of individual input pixels; means for delaying said input pixels by a predetermined number of pixel locations per line and by a predetermined number of scan lines; means for generating an output pixel value using one of said delayed pixels; means for generating a signal representing the local minimum signal level of said input pixels; means for generating a signal representing the local maximum signal level of said input pixels; means for selecting either the said local minimum or said local maximum based on said output pixel; means for generating an error signal using said selected minimum or maximum signal and the said delayed pixel used in said thresholding comparison, such that said error signal may contain either positive or negative signal information; means for weighting said error signal using a fixed number of predetermined factors; means for adding or subtracting said weighted error signal from said fixed number of remaining delayed pixel values thus generating new delayed pixel values; and means for checking to insure that said new delayed pixel values are within a predetermined range.
Claim 9
Dependent Claim
16 words
The apparatus in claim 6 wherein said local maximum signal is generated by a peak detector.
Claim 10
Dependent Claim
16 words
The apparatus in claim 6 wherein said local minimum signal is generated by a valley detector.
Claim 11
Dependent Claim
29 words
The apparatus in claim 6 wherein said output value generation means is comprised of a random access memory that is loaded with a predefined output function via external means.
Claim 12
Dependent Claim
25 words
The apparatus in claim 6 wherein said output value generation means is comprised of a programmable read only memory which contains a predefined output function.
Claim 13
Dependent Claim
30 words
The apparatus in claim 6 wherein said selection of local minimum or maximum values is a two to one multiplexer controlled by the most significant bit of the output pixel.
Claim 14
Dependent Claim
20 words
The apparatus in claim 6 wherein said delaying means further comprises: a line delaying means and a pixel delaying means.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1994-10-21 | 1995-04-22 | 1995-10-22 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1998-10-21 | 1999-04-22 | 1999-10-22 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2002-10-21 | 2003-04-22 | 2003-10-22 | $7700.00 | Window Closed / Lapsed |