US4918543A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Apparatus for thresholding an image signal
Assignee: Eastman Kodak Co
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Filing: 1989-01-24
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Granted: 1990-04-17
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Expires: 2009-01-24
Abstract
Abstract This invention relates to an apparatus for converting a grayscale image to a bitonal image which provides improved tonal rendition with minimal loss of resolution. The invention attenuates the low spatial frequency component of the digital image and uses a similarly attenuated thresholder to convert the image to a bitonal image. When used with a dither type thresholder, this technique allows for simultaneous "continuous tone" and "line art" thresholding with minimal circuit complexity.
Inventors
- 👤 Eugene M. Petilli
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 12:07
CPC Classifications
H; H04; H04N; H04N1/00; H04N1/40; H04N1/409; H04N1/4092; H04N1/405; H04N1/4051
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
111 words
An image signal processing apparatus comprising: image scanning means having optical means for scanning an original in a two-dimensional manner, and photoelectric converting means for converting an optical image obtained by said optical means into an electrical signal; DC offset means for removing a predetermined DC level from said peak to peak electrical signal to provide a predetermined DC offset; analog to digital conversion means for converting said electrical signal into a digital signal; digital attenuation filter means having less than unity gain for providing a DC attenuation of said electrical signal; and dither converter means using at least a main dither matrix for performing dither conversion of said digital signal.
Claim 2
Dependent Claim
111 words
An image signal processing apparatus comprising: image scanning means having optical means for scanning an original in a two-dimensional manner, and photoelectric converting means for converting an optical image obtained by said optical means into an electrical signal; DC offset means for removing a predetermined DC level from said peak to peak electrical signal to provide a predetermined DC offset; analog to digital conversion means for converting said electrical signal into a digital signal; digital attenuation filter means having less than unity gain for providing a DC attenuation of said electrical signal; and dither converter means using at least a main dither matrix for performing dither conversion of said digital signal.
Claim 3
Dependent Claim
18 words
An image signal processing apparatus according to claim 1 wherein said dither converter means comprises plural sub-dither matrices.
Claim 4
Dependent Claim
22 words
An image signal processing apparatus according to claim 2 wherein said digital attenuation filter means is a convolution finite impulse response filter.
Claim 5
Dependent Claim
37 words
An image signal processing apparatus according to claim 2 wherein said plural sub-dither matrices are arranged in said main dither matrix such that the averages of dither levels in said sub-dither matrices represent a high spatial frequency.
Claim 6
Dependent Claim
26 words
An image signal processing apparatus according to claim 3 wherein said processing apparatus further includes a second convolution finite impulse response filter for providing image enhancement.
Claim 7
Dependent Claim
27 words
An image signal processing apparatus according to claim 5 wherein said attenuation filter and said second convolution finite impulse response filter are combined in a single filter.
Claim 8
Dependent Claim
81 words
In an apparatus for processing image signals derived by raster scanning document originals the combination comprising: means for converting said raster scanned image signal into a digital signal; DC offset means for removing a predetermined DC level from said digital signal resulting in a predetermined DC offset; digital attenuation means having less than unity gain for providing a DC attenuation of said digital signal; and dither converter means including a main dither matrix for performing dither conversion of said digital signals.
Claim 9
Dependent Claim
81 words
In an apparatus for processing image signals derived by raster scanning document originals the combination comprising: means for converting said raster scanned image signal into a digital signal; DC offset means for removing a predetermined DC level from said digital signal resulting in a predetermined DC offset; digital attenuation means having less than unity gain for providing a DC attenuation of said digital signal; and dither converter means including a main dither matrix for performing dither conversion of said digital signals.
Claim 10
Dependent Claim
23 words
An apparatus for processing image signals according to claim 1 wherein said digital attenuation filter means is a convolution finite impulse response filter.
Claim 11
Dependent Claim
27 words
An apparatus for processing image signals according to claim 8 wherein said processing apparatus further include a second convolution finite impulse response filter for providing image enhancement.
Claim 12
Dependent Claim
28 words
An apparatus for processing image signals according to claim 9 wherein said attenuation filter and said second convolution finite impulse response filter are combined in a single filter.
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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) | 1993-04-16 | 1993-10-16 | 1994-04-17 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1997-04-16 | 1997-10-16 | 1998-04-17 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2001-04-16 | 2001-10-16 | 2002-04-17 | $7700.00 | Window Closed / Lapsed |