Patent US6826310B2 successfully refreshed from Google Patents.
US6826310B2
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Automatic contrast enhancement
Assignee: COREL HOLDINGS Corp
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Filing: 2001-07-06
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Granted: 2004-11-30
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Expires: 2021-07-06
Abstract
Abstract A method of automatic contrast correction comprises providing digital image data, representing the data in the form of a brightness histogram, determining a measure of central tendency for said histogram, adding a shift value to the measure of central tendency to provide an adjusted measure of central tendency, using the both the determined and adjusted measures of central tendency to determine the exponent of a tone reproduction curve, and applying the tone reproduction curve to the brightness values of the image. Additionally, the method may provide further correction by applying to the brightness values of the image an S-shaped tone reproduction curve that does not change a measure of central tendency of the brightness histogram.
Inventors
- 👤 Mikhail Ivanovich Trifonov
- 👤 Olga Vadimovna Sharonova
- 👤 Kryzstof Antoni Zaklika
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 11:29
CPC Classifications
G; G06; G06T; G06T5/00; G06T5/40; G06T5/90; G06T5/92
Claims Analysis
Total Claims: 33
Claim 1
Independent Claim
85 words
A method of automatic contrast correction comprising providing digital image data, representing the data in the form of a brightness histogram, determining a measure of central tendency for said histogram as a determined measure of central tendency, adding a shift value to the measure of central tendency to provide an adjusted measure of central tendency, computing a tone reproduction curve by a ratio containing logarithms of determined and adjusted measures of central tendency, and applying this tone reproduction curve to brightness values of the image.
Claim 2
Independent Claim
85 words
A method of automatic contrast correction comprising providing digital image data, representing the data in the form of a brightness histogram, determining a measure of central tendency for said histogram as a determined measure of central tendency, adding a shift value to the measure of central tendency to provide an adjusted measure of central tendency, computing a tone reproduction curve by a ratio containing logarithms of determined and adjusted measures of central tendency, and applying this tone reproduction curve to brightness values of the image.
Claim 3
Dependent Claim
57 words
The method of claim 1 wherein computing the exponent of a tone reproduction curve, γ, is performed by the equation. γ= ln ( L orig /N )/ ln ( L adj /N ) where L orig represents the determined measure of central tendency, L adj the adjusted measure of central tendency, and N the maximum image brightness.
Claim 4
Dependent Claim
57 words
The method of claim 1 wherein computing the exponent of a tone reproduction curve, γ, is performed by the equation. γ=( ln L orig −ln N )/( ln L adj −ln N ) where L orig represents the determined measure of central tendency, L adj the adjusted measure of central tendency, and N the maximum image brightness.
Claim 5
Dependent Claim
70 words
The method of claim 1 wherein the shift value is zero for a mean brightness of zero and increases to a maximum with increasing mean brightness before falling to zero at an intermediate mean brightness, and as mean brightness increases beyond the intermediate mean brightness, the shift value decreases, falling to a negative, minimum value before increasing to zero again at the maximum mean brightness that the image can have.
Claim 6
Dependent Claim
49 words
The method of claim 1 wherein the tone reproduction curve is given by: L′ i =N ( L i /N ) 1/γ where L i is any original brightness value, L′ i a corresponding enhanced brightness value, N is the largest possible brightness value, and γ is an exponent.
Claim 7
Dependent Claim
25 words
The method of claim 5 wherein the measure of central tendency of the brightness histogram is the mean brightness of the histogram, L mean .
Claim 8
Dependent Claim
143 words
The method of claim 6 wherein the shift is provided by the equation: δ L = q ( L m e a n / N ) r ( 1 - [ L m e a n / N ] ) s ( [ t - L m e a n ] / N ) u exp ( v [ L m e a n / N ] w ) exp { x ( [ y - L m e a n ] / N ) z } where q, r, s, t, u, v, w, x, y and z are adjustable constants.
Claim 9
Dependent Claim
25 words
The method of claim 1 wherein the measure of central tendency of the brightness histogram is the mean brightness of the histogram, L mean .
Claim 10
Dependent Claim
28 words
The method of claim 1 wherein there is also applied an S-shaped tone reproduction curve that does not change a measure of central tendency of the brightness histogram.
Claim 11
Dependent Claim
43 words
The method of claim 1 wherein after applying the tone reproduction curve to brightness values of the image, applying to brightness values of the image an S-shaped tone reproduction curve that does not change a measure of central tendency of the brightness histogram.
Claim 12
Dependent Claim
70 words
The method of claim 10 wherein a shift value is added to the measure of central tendency to provide an adjusted measure of central tendency, computing the exponent of a tone reproduction curve by means of a ratio containing the logarithms of the determined and adjusted measures of central tendency, and applying to the brightness values of the image a tone reproduction curve derived from the properties of the image.
Claim 13
Dependent Claim
70 words
The method of claim 11 wherein the shift value is zero for a mean brightness of zero and increases to a maximum with increasing mean brightness before falling to zero at an intermediate mean brightness, and as mean brightness increases beyond the intermediate mean brightness, the shift value decreases falls to a negative, minimum value before increasing to zero again at the maximum mean brightness that the image can have.
Claim 14
Dependent Claim
49 words
The method of claim 11 wherein the tone reproduction curve is given by. L′ i =N ( L i /N ) 1/γ where L i is any original brightness value, L′ i a corresponding enhanced brightness value, N is the largest possible brightness value, and γ is an exponent.
Claim 15
Dependent Claim
25 words
The method of claim 13 wherein the measure of central tendency of the brightness histogram is the mean brightness of the histogram, L mean .
Claim 16
Dependent Claim
25 words
The method of claim 11 wherein the measure of central tendency of the brightness histogram is the mean brightness of the histogram, L mean .
Claim 17
Dependent Claim
143 words
The method of claim 15 wherein the shift is provided by the equation: δ L = q ( L m e a n / N ) r ( 1 - [ L m e a n / N ] ) s ( [ t - L m e a n ] / N ) u exp ( v [ L m e a n / N ] w ) exp { x ( [ y - L m e a n ] / N ) z } where q, r, s, t, u, v, w, x, y and z are adjustable constants.
Claim 18
Dependent Claim
33 words
The method of claim 11 wherein the contrast adjustment is performed in a color space selected from the group consisting of CIE L*u*v*, CIE L*a*b*, YIQ, YUV, YCbCr, YES, YCC, HVC and HSV.
Claim 19
Dependent Claim
19 words
A computer comprising hardware and software that can execute the method of claim 11 from memory in the computer.
Claim 20
Dependent Claim
19 words
A computer comprising hardware and software that can execute the method of claim 10 from memory in the computer.
Claim 21
Dependent Claim
33 words
The method of claim 1 wherein the contrast adjustment is performed in a color space selected from the group consisting of CIE L*u*v*, CIE L*a*b*, YIQ, YUV, YCbCr, YES, YCC, HVC and HSV.
Claim 22
Dependent Claim
14 words
The method of claim 1 wherein the shift is determined from a shift curve.
Claim 23
Dependent Claim
71 words
The method of claim 1 wherein the shift is determined from a shift curve with a shape selected from the group consisting of: a) a curve with two distinct, but contiguous sections, a first section having a positive integration value and second section having a negative integration value; d) a curve with only positive integration values under the curve; and e) a curve with only negative integration values under the curve.
Claim 24
Dependent Claim
42 words
The method of claim 1 wherein the shift is determined from a shift curve with a shape that has positive integration values in relatively lower brightness areas of the histogram and negative integration values in relatively higher brightness areas of the histogram.
Claim 25
Dependent Claim
19 words
A computer comprising hardware and software that can execute the method of claim 1 from memory in the computer.
Claim 26
Independent Claim
55 words
A method of contrast correction comprising providing digital image data, representing the data in the form of a brightness histogram, determining a measure of central tendency for said histogram, and applying to brightness values of the image an S-shaped tone reproduction curve that does not change a measure of central tendency of the brightness histogram.
Claim 27
Independent Claim
55 words
A method of contrast correction comprising providing digital image data, representing the data in the form of a brightness histogram, determining a measure of central tendency for said histogram, and applying to brightness values of the image an S-shaped tone reproduction curve that does not change a measure of central tendency of the brightness histogram.
Claim 28
Dependent Claim
15 words
The method of claim 25 wherein the S-shape tone reproduction curve is a tilde function.
Claim 29
Dependent Claim
26 words
The method of claim 26 wherein at least one of the parameters of the tilde function is determined by linear regression on the integral brightness histogram.
Claim 30
Dependent Claim
19 words
A computer comprising hardware and software that can execute the method of claim 25 from memory in the computer.
Claim 31
Independent Claim
75 words
A method of automatic contrast correction comprising providing digital image data, representing the data in the form of a brightness histogram, determining a measure of central tendency for said histogram, and applying to brightness values of the image an S-shaped tone reproduction curve that does not change a measure of central tendency of the brightness histogram, wherein the shape of the S-shaped tone reproduction curve is determined by linear regression on the integral brightness histogram.
Claim 32
Independent Claim
75 words
A method of automatic contrast correction comprising providing digital image data, representing the data in the form of a brightness histogram, determining a measure of central tendency for said histogram, and applying to brightness values of the image an S-shaped tone reproduction curve that does not change a measure of central tendency of the brightness histogram, wherein the shape of the S-shaped tone reproduction curve is determined by linear regression on the integral brightness histogram.
Claim 33
Dependent Claim
15 words
The method of claim 29 wherein the S-shape tone reproduction curve is a tilde function.
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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) | 2007-11-30 | 2008-05-31 | 2008-11-30 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2011-11-30 | 2012-05-31 | 2012-11-30 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2015-11-30 | 2016-05-31 | 2016-11-30 | $7700.00 | Window Closed / Lapsed |