Patent US5481628A successfully refreshed from Google Patents.
US5481628A
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US
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Method and apparatus for spatially variant filtering
Assignee: Eastman Kodak Co
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Filing: 1993-03-09
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Granted: 1996-01-02
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Expires: 2013-03-09
Abstract
Abstract An adaptive spatial filter for digital image processing selectively performs spatial high pass filtering of an input digital signal to produce an output pixel value having an enhanced signal level using a gain factor that effects a variable degree of enhancement of the input pixel, so that pixels whose activity values are close to an iteratively adjustable activity threshold level will be emphasized significantly less than pixels whose associated activity values are substantially above the threshold level. The activity threshold level is selectively updated at the end of a scan line in accordance with prescribed spatial activity criteria, so as to effectively prevent discontinuities in the threshold level during line-by-line adjustment and to take into account how `noisy` the background is. Potential corruption of the updated value of a pixel by an edge portion of the image is avoided by requiring that pixels which are associated with background or signal regions of the image be respectively less than or greater than a local mean value. Otherwise the pixel values are not modified.
Inventors
- 👤 Mohsen Ghaderi
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 19:41
CPC Classifications
G; G06; G06T; G06T5/00; G06T5/20
Claims Analysis
Total Claims: 27
Claim 1
Independent Claim
303 words
A method of processing an input digital image containing an array of input pixels having associated digital input signals which are to be processed to produce digital output signals representative of the values of output pixels of an enhanced output digital image, said method comprising the steps of: (a) providing an adaptive spatial filter mechanism which selectively performs spatial high pass filtering of successive portions of an input digital signal associated with a respective input pixel of an input digital image in accordance with a first prescribed relationship between a variation in spatial activity content within an image window containing said input pixel and an adjustable threshold level; (b) applying a digital input signal to the adaptive filter mechanism provided in step (a), so as to produce a digital output signal associated with a respective output pixel of said output digital image; and wherein said adaptive spatial filter mechanism is operative to selectively adjust said adjustable threshold level to a new threshold level for each of said successive portions of said input digital image in accordance with the contents of a respective portion of said digital input image being processed, and wherein, for each successive portion of said input digital image to be processed, said adaptive spatial filter mechanism is operative to generate a respective prospective threshold level in accordance with the contents of said each successive portion of said digital input image being processed, and wherein, for a respective one of said successive portions of said input digital image, said adaptive spatial filter mechanism is operative to selectively employ either its prospective threshold level or the previous threshold level as said adjustable threshold level in dependence upon a prescribed difference in contents of said respective one of said successive portions of said image and another of said successive portions of said image.
Claim 2
Independent Claim
303 words
A method of processing an input digital image containing an array of input pixels having associated digital input signals which are to be processed to produce digital output signals representative of the values of output pixels of an enhanced output digital image, said method comprising the steps of: (a) providing an adaptive spatial filter mechanism which selectively performs spatial high pass filtering of successive portions of an input digital signal associated with a respective input pixel of an input digital image in accordance with a first prescribed relationship between a variation in spatial activity content within an image window containing said input pixel and an adjustable threshold level; (b) applying a digital input signal to the adaptive filter mechanism provided in step (a), so as to produce a digital output signal associated with a respective output pixel of said output digital image; and wherein said adaptive spatial filter mechanism is operative to selectively adjust said adjustable threshold level to a new threshold level for each of said successive portions of said input digital image in accordance with the contents of a respective portion of said digital input image being processed, and wherein, for each successive portion of said input digital image to be processed, said adaptive spatial filter mechanism is operative to generate a respective prospective threshold level in accordance with the contents of said each successive portion of said digital input image being processed, and wherein, for a respective one of said successive portions of said input digital image, said adaptive spatial filter mechanism is operative to selectively employ either its prospective threshold level or the previous threshold level as said adjustable threshold level in dependence upon a prescribed difference in contents of said respective one of said successive portions of said image and another of said successive portions of said image.
Claim 3
Dependent Claim
172 words
A method according to claim 1, wherein, for a respective one of said successive portions of said input digital image to be processed, said adaptive spatial filter mechanism is operative to generate said respective prospective threshold level in accordance with a prescribed combination of the threshold level of a previous one said successive portions of said input digital image and an activity level parameter representative of the spatial variation of pixels located in a region other than a low spatial frequency region of said digital input image, and wherein, for said respective one of said successive portions of said input digital image, said adaptive spatial filter mechanism is operative to selectively employ either its prospective threshold level or the threshold level of said previous one said successive portions of said input digital image, in dependence upon a prescribed difference between the threshold level of another of said successive portions of said input digital image and said activity level parameter of said respective one of said successive portions of said input digital image.
Claim 4
Dependent Claim
79 words
A method according to claim 2, wherein said adaptive spatial filter mechanism is operative to employ said prospective threshold level in response to said prescribed difference between the threshold level of another of said successive portions of said input digital image and said activity level parameter of said respective one of said successive portions of said input digital image being less than a predetermined fraction of the threshold level of said previous successive portion of said input digital image.
Claim 5
Dependent Claim
77 words
A method according to claim 3, wherein said adaptive spatial filter mechanism is operative to employ said prospective threshold level in response to said prescribed difference between the threshold level of another of said successive portions of said input digital image and said activity level parameter of said respective one of said successive portions of said input digital image being less than one-fourth of the threshold level of said previous successive portion of said input digital image.
Claim 6
Independent Claim
312 words
A method of processing an input digital image containing an array of input pixels having associated digital input signals which are to be processed to produce digital output signals representative of the values of output pixels of an enhanced output digital image, said method comprising the steps of: (a) providing an adaptive spatial filter mechanism which selectively performs spatial high pass filtering of successive portions of an input digital signal associated with a respective input pixel of an input digital image in accordance with a first prescribed relationship between a variation in spatial activity content within an image window containing said input pixel and an adjustable threshold level; (b) applying a digital input signal to the adaptive filter mechanism provided in step (a), so as to produce a digital output signal associated with a respective output pixel of said output digital image; and wherein said adaptive spatial filter mechanism is operative to selectively adjust said adjustable threshold level to a new threshold level for each of said successive portions of said input digital image in accordance with the contents of a respective portion of said digital input image being processed, and wherein, for each successive portion of said input digital image to be processed, said adaptive spatial filter mechanism is operative to generate a respective prospective threshold level in accordance with the contents of said each successive portion of said digital input image being processed, and wherein, for a respective one of said successive portions of said input digital image, said adaptive spatial filter mechanism is operative to selectively employ either its prospective threshold level or the previous threshold level as said adjustable threshold level in dependence upon a predetermined relationship between the adjustable threshold level of another of said successive portions of said input digital image and background level of said another of said successive portions of said input digital image.
Claim 7
Independent Claim
312 words
A method of processing an input digital image containing an array of input pixels having associated digital input signals which are to be processed to produce digital output signals representative of the values of output pixels of an enhanced output digital image, said method comprising the steps of: (a) providing an adaptive spatial filter mechanism which selectively performs spatial high pass filtering of successive portions of an input digital signal associated with a respective input pixel of an input digital image in accordance with a first prescribed relationship between a variation in spatial activity content within an image window containing said input pixel and an adjustable threshold level; (b) applying a digital input signal to the adaptive filter mechanism provided in step (a), so as to produce a digital output signal associated with a respective output pixel of said output digital image; and wherein said adaptive spatial filter mechanism is operative to selectively adjust said adjustable threshold level to a new threshold level for each of said successive portions of said input digital image in accordance with the contents of a respective portion of said digital input image being processed, and wherein, for each successive portion of said input digital image to be processed, said adaptive spatial filter mechanism is operative to generate a respective prospective threshold level in accordance with the contents of said each successive portion of said digital input image being processed, and wherein, for a respective one of said successive portions of said input digital image, said adaptive spatial filter mechanism is operative to selectively employ either its prospective threshold level or the previous threshold level as said adjustable threshold level in dependence upon a predetermined relationship between the adjustable threshold level of another of said successive portions of said input digital image and background level of said another of said successive portions of said input digital image.
Claim 8
Dependent Claim
184 words
A method according to claim 5, wherein, for a respective one of said successive portion of said input digital image to be processed, said adaptive spatial filter mechanism is operative to generate said respective prospective threshold level in accordance with a prescribed combination of the threshold level of a previous one said successive portions of said input digital image and an activity level parameter representative of the spatial variation of pixels located in a region other than a low spatial frequency region of said digital input image, and wherein, for said respective one of said successive portions of said input digital image, said adaptive spatial filter mechanism is operative to selectively employ either its prospective threshold level or the threshold level of said previous one said successive portions of said input digital image, in dependence upon whether the threshold level of said previous one of said successive portions of said input digital image is no greater than a low frequency activity level parameter representative of the low frequency spatial variation of pixels located in a low spatial frequency region of said digital input image.
Claim 9
Dependent Claim
49 words
A method according to claim 6, wherein said adaptive spatial filter mechanism is operative to employ its prospective threshold level in response to the threshold level of said previous one of said successive portions of said input digital image being no greater than said low frequency activity level parameter.
Claim 10
Dependent Claim
58 words
A method according to claim 6, wherein said adaptive spatial filter mechanism is operative to employ the threshold level of said previous one of said successive portions of said image in response to the threshold level of said previous one of said successive portions of said input digital image being greater than said low frequency activity level parameter.
Claim 11
Independent Claim
391 words
A method of processing an input digital image containing an array of input pixels having associated digital input signals which are to be processed to produce digital output signals representative of the values of output pixels of an enhanced output digital image, said method comprising the steps of: (a) providing an adaptive spatial filter mechanism which selectively performs spatial high pass filtering of successive portions of an input digital signal associated with a respective input pixel of an input digital image in accordance with a first prescribed relationship between a variation in spatial activity content within an image window containing said input pixel and an adjustable threshold level; (b) applying a digital input signal to the adaptive filter mechanism provided in step (a), so as to produce a digital output signal associated with a respective output pixel of said output digital image; and wherein said adaptive spatial filter mechanism is operative to selectively adjust said adjustable threshold level to a new threshold level for each of said successive portions of said input digital image in accordance with the contents of a respective portion of said digital input image being processed, and wherein said array of input pixels comprises a plurality of lines of pixels, and wherein, for each line of said input digital image to be processed, said adaptive spatial filter mechanism is operative to generate a respective prospective threshold level in accordance with a prescribed combination of the threshold level of a previous line of said input digital image and an activity level parameter representative of the spatial variation of pixels located in a region other than a low spatial frequency region of said digital input image, and wherein, for a respective line of said input digital image, said adaptive spatial filter mechanism is operative to selectively employ its prospective threshold level as said adjustable threshold level in dependence upon a prescribed difference between the threshold level of another line of said input digital image and said activity level parameter of said respective line of said input digital image, or in response to satisfaction of a predetermined relationship between the adjustable threshold level of the previous line of said input digital image and a low frequency activity level parameter representative of the low frequency spatial variation of pixels located in a low spatial frequency region of said digital input image.
Claim 12
Independent Claim
391 words
A method of processing an input digital image containing an array of input pixels having associated digital input signals which are to be processed to produce digital output signals representative of the values of output pixels of an enhanced output digital image, said method comprising the steps of: (a) providing an adaptive spatial filter mechanism which selectively performs spatial high pass filtering of successive portions of an input digital signal associated with a respective input pixel of an input digital image in accordance with a first prescribed relationship between a variation in spatial activity content within an image window containing said input pixel and an adjustable threshold level; (b) applying a digital input signal to the adaptive filter mechanism provided in step (a), so as to produce a digital output signal associated with a respective output pixel of said output digital image; and wherein said adaptive spatial filter mechanism is operative to selectively adjust said adjustable threshold level to a new threshold level for each of said successive portions of said input digital image in accordance with the contents of a respective portion of said digital input image being processed, and wherein said array of input pixels comprises a plurality of lines of pixels, and wherein, for each line of said input digital image to be processed, said adaptive spatial filter mechanism is operative to generate a respective prospective threshold level in accordance with a prescribed combination of the threshold level of a previous line of said input digital image and an activity level parameter representative of the spatial variation of pixels located in a region other than a low spatial frequency region of said digital input image, and wherein, for a respective line of said input digital image, said adaptive spatial filter mechanism is operative to selectively employ its prospective threshold level as said adjustable threshold level in dependence upon a prescribed difference between the threshold level of another line of said input digital image and said activity level parameter of said respective line of said input digital image, or in response to satisfaction of a predetermined relationship between the adjustable threshold level of the previous line of said input digital image and a low frequency activity level parameter representative of the low frequency spatial variation of pixels located in a low spatial frequency region of said digital input image.
Claim 13
Dependent Claim
72 words
A method according to claim 9, wherein said adaptive spatial filter mechanism is operative to employ said prospective threshold level in response to said prescribed difference between the threshold level of said another line of said input digital image and said activity level parameter of said respective line of said input digital image being less than a predetermined fraction of the threshold level of said previous line of said input digital image.
Claim 14
Dependent Claim
76 words
A method according to claim 9, wherein said adaptive spatial filter mechanism is operative to employ the threshold level of a previous line in response to said prescribed difference between the threshold level of said another line of said input digital image and said activity level parameter of said respective line of said input digital image being no less than a predetermined fraction of said threshold level of said previous line of said input digital image.
Claim 15
Dependent Claim
45 words
A method according to claim 9, wherein said adaptive spatial filter mechanism is operative to employ its prospective threshold level in response to the threshold level of said previous line of said input digital image being no greater than said low frequency activity level parameter.
Claim 16
Dependent Claim
50 words
A method according to claim 9, wherein said adaptive spatial filter mechanism is operative to employ the threshold level of said previous line of said image in response to the threshold level of said previous line of said input digital image being greater than said low frequency activity level parameter.
Claim 17
Independent Claim
259 words
An apparatus for processing digital input signals representative of input pixels of an input digital image to produce digital output signals representative of output pixels of an enhanced output digital image comprising: an input unit to which said digital input signals are coupled; and an adaptive spatial filter which selectively performs spatial high pass filtering of successive portions of an input digital signal associated with a respective input pixel of said input digital image in accordance with a first prescribed relationship between a variation in spatial activity content within an image window containing said input pixel and an adjustable threshold level, and wherein said adaptive spatial filter is operative to selectively adjust said adjustable threshold level to a new threshold level for each of said successive portions of said input digital image in accordance with the contents of a respective portion of said digital input image being processed, and wherein said input digital image comprises a plurality of lines of pixels and wherein, for each successive line said input digital image, said adaptive spatial filter mechanism is operative to generate a respective prospective threshold level in accordance with the contents of said each successive line, and wherein, for a respective line of said input digital image, said adaptive spatial filter mechanism is operative to selectively employ either its prospective threshold level or the previous threshold level as said adjustable threshold level in dependence upon a prescribed difference in contents of said respective one of said successive portions of said image and another of said successive portions of said image.
Claim 18
Independent Claim
259 words
An apparatus for processing digital input signals representative of input pixels of an input digital image to produce digital output signals representative of output pixels of an enhanced output digital image comprising: an input unit to which said digital input signals are coupled; and an adaptive spatial filter which selectively performs spatial high pass filtering of successive portions of an input digital signal associated with a respective input pixel of said input digital image in accordance with a first prescribed relationship between a variation in spatial activity content within an image window containing said input pixel and an adjustable threshold level, and wherein said adaptive spatial filter is operative to selectively adjust said adjustable threshold level to a new threshold level for each of said successive portions of said input digital image in accordance with the contents of a respective portion of said digital input image being processed, and wherein said input digital image comprises a plurality of lines of pixels and wherein, for each successive line said input digital image, said adaptive spatial filter mechanism is operative to generate a respective prospective threshold level in accordance with the contents of said each successive line, and wherein, for a respective line of said input digital image, said adaptive spatial filter mechanism is operative to selectively employ either its prospective threshold level or the previous threshold level as said adjustable threshold level in dependence upon a prescribed difference in contents of said respective one of said successive portions of said image and another of said successive portions of said image.
Claim 19
Dependent Claim
148 words
An apparatus according to claim 14, wherein, for a respective line of said input digital image, said adaptive spatial filter mechanism is operative to generate said respective prospective threshold level in accordance with a prescribed combination of the threshold level of a previous line of said input digital image and an activity level parameter representative of the spatial variation of pixels located in a region other than a low spatial frequency region of said digital input image, and wherein, for said respective line of said input digital image, said adaptive spatial filter mechanism is operative to selectively employ either its prospective threshold level or the threshold level of said previous line of said input digital image, in dependence upon a prescribed difference between the threshold level of another line of said input digital image and said activity level parameter of said respective line of said input digital image.
Claim 20
Dependent Claim
70 words
An apparatus according to claim 15, wherein said adaptive spatial filter is operative to employ said prospective threshold level in response to said prescribed difference between the threshold level of another line of said input digital image and said activity level parameter of said respective line of said input digital image being less than a predetermined fraction of the threshold level of said previous line of said input digital image.
Claim 21
Dependent Claim
166 words
An apparatus according to claim 16, wherein, for a respective line of said input digital image to be processed, said adaptive spatial filter mechanism is operative to generate said respective prospective threshold level in accordance with a prescribed combination of the threshold level of a previous line of said input digital image and an activity level parameter representative of the spatial variation of pixels located in a region other than a low spatial frequency region of said digital input image, and wherein, for said respective line of said input digital image, said adaptive spatial filter mechanism is operative to selectively employ either its prospective threshold level or the threshold level of said previous line of said input digital image, in dependence upon whether the threshold level of said previous line of said input digital image is no greater than a low frequency activity level parameter representative of the low frequency spatial variation of pixels located in a low spatial frequency region of said digital input image.
Claim 22
Dependent Claim
45 words
An apparatus according to claim 17, wherein said adaptive spatial filter mechanism is operative to employ its prospective threshold level in response to the threshold level of said previous line of said input digital image being no greater than said low frequency activity level parameter.
Claim 23
Dependent Claim
52 words
An apparatus according to claim 17, wherein said adaptive spatial filter mechanism is operative to employ the threshold level of said previous line of said input digital image in response to the threshold level of said previous line of said input digital image being greater than said low frequency activity level parameter.
Claim 24
Independent Claim
267 words
An apparatus for processing digital input signals representative of input pixels of an input digital image to produce digital output signals representative of output pixels of an enhanced output digital image comprising:. an input unit to which said digital input signals are coupled; and an adaptive spatial filter which selectively performs spatial high pass filtering of successive portions of an input digital signal associated with a respective input pixel of said input digital image in accordance with a first prescribed relationship between a variation in spatial activity content within an image window containing said input pixel and an adjustable threshold level, and wherein said adaptive spatial filter is operative to selectively adjust said adjustable threshold level to a new threshold level for each of said successive portions of said input digital image in accordance with the contents of a respective portion of said digital input image being processed, and wherein said input digital image comprises a plurality of lines of pixels and wherein, for each successive line said input digital image, said adaptive spatial filter mechanism is operative to generate a respective prospective threshold level in accordance with the contents of said each successive line of said digital input image, and wherein, for a respective line of said input digital image, said adaptive spatial filter mechanism is operative to selectively employ either its prospective threshold level or the previous threshold level as said adjustable threshold level in dependence upon a predetermined relationship between the adjustable threshold level of another line of said input digital image and background level of said another line of said input digital image.
Claim 25
Independent Claim
267 words
An apparatus for processing digital input signals representative of input pixels of an input digital image to produce digital output signals representative of output pixels of an enhanced output digital image comprising:. an input unit to which said digital input signals are coupled; and an adaptive spatial filter which selectively performs spatial high pass filtering of successive portions of an input digital signal associated with a respective input pixel of said input digital image in accordance with a first prescribed relationship between a variation in spatial activity content within an image window containing said input pixel and an adjustable threshold level, and wherein said adaptive spatial filter is operative to selectively adjust said adjustable threshold level to a new threshold level for each of said successive portions of said input digital image in accordance with the contents of a respective portion of said digital input image being processed, and wherein said input digital image comprises a plurality of lines of pixels and wherein, for each successive line said input digital image, said adaptive spatial filter mechanism is operative to generate a respective prospective threshold level in accordance with the contents of said each successive line of said digital input image, and wherein, for a respective line of said input digital image, said adaptive spatial filter mechanism is operative to selectively employ either its prospective threshold level or the previous threshold level as said adjustable threshold level in dependence upon a predetermined relationship between the adjustable threshold level of another line of said input digital image and background level of said another line of said input digital image.
Claim 26
Independent Claim
349 words
An apparatus for processing digital input signals representative of input pixels of an input digital image to produce digital output signals representative of output pixels of an enhanced output digital image comprising: an input unit to which said digital input signals are coupled; and an adaptive spatial filter which selectively performs spatial high pass filtering of successive portions of an input digital signal associated with a respective input pixel of said input digital image in accordance with a first prescribed relationship between a variation in spatial activity content within an image window containing said input pixel and an adjustable threshold level, and wherein said adaptive spatial filter is operative to selectively adjust said adjustable threshold level to a new threshold level for each of said successive portions of said input digital image in accordance with the contents of a respective portion of said digital input image being processed, and wherein said array of input pixels comprises a plurality of lines of pixels, and wherein, for each line of said input digital image to be processed, said adaptive spatial filter mechanism is operative to generate a respective prospective threshold level in accordance with a prescribed combination of the threshold level of a previous line of said input digital image and an activity level parameter representative of the spatial variation of pixels located in a region other than a low spatial frequency region of said digital input image, and wherein, for a respective line of said input digital image, said adaptive spatial filter mechanism is operative to selectively employ its prospective threshold level as said adjustable threshold level in dependence upon a prescribed difference between the threshold level of another line of said input digital image and said activity level parameter of said respective line of said input digital image, or in response to satisfaction of a predetermined relationship between the adjustable threshold level of the previous line of said input digital image and a low frequency activity level parameter representative of the low frequency spatial variation of pixels located in a low spatial frequency region of said digital input image.
Claim 27
Independent Claim
349 words
An apparatus for processing digital input signals representative of input pixels of an input digital image to produce digital output signals representative of output pixels of an enhanced output digital image comprising: an input unit to which said digital input signals are coupled; and an adaptive spatial filter which selectively performs spatial high pass filtering of successive portions of an input digital signal associated with a respective input pixel of said input digital image in accordance with a first prescribed relationship between a variation in spatial activity content within an image window containing said input pixel and an adjustable threshold level, and wherein said adaptive spatial filter is operative to selectively adjust said adjustable threshold level to a new threshold level for each of said successive portions of said input digital image in accordance with the contents of a respective portion of said digital input image being processed, and wherein said array of input pixels comprises a plurality of lines of pixels, and wherein, for each line of said input digital image to be processed, said adaptive spatial filter mechanism is operative to generate a respective prospective threshold level in accordance with a prescribed combination of the threshold level of a previous line of said input digital image and an activity level parameter representative of the spatial variation of pixels located in a region other than a low spatial frequency region of said digital input image, and wherein, for a respective line of said input digital image, said adaptive spatial filter mechanism is operative to selectively employ its prospective threshold level as said adjustable threshold level in dependence upon a prescribed difference between the threshold level of another line of said input digital image and said activity level parameter of said respective line of said input digital image, or in response to satisfaction of a predetermined relationship between the adjustable threshold level of the previous line of said input digital image and a low frequency activity level parameter representative of the low frequency spatial variation of pixels located in a low spatial frequency region of said digital input image.
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