EP0525527A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Look-up table based gamma and inverse gamma correction for high-resolution frame buffers
Assignee: International Business Machines Corp
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Filing: 1992-07-16
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Granted: —
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Expires: 2012-07-16
Abstract
Abstract 5 n7 An image display system includes an input to a source (10, 12, 14) of image pixel data wherein each pixel is expressed as an M-bit value within a non-linear range of values. A first LUT (16) is coupled to an output of the source for converting each M-bit pixel value to an N-bit value within a linear range of values. An image memory, or frame buffer (18), has an input coupled to an output of the first LUT for storing the N-bit pixel values. The system further includes a second LUT (20) coupled to an output of the frame buffer for converting N-bit pixel values output by the frame buffer to P-bit pixel values within a non-linear range of values. The converted values are subsequently applied to a display (24). In an exemplary embodiment, the first LUT stores gamma corrected pixel values and the second LUT stores inverse gamma corrected pixel values. Preferably the second LUT stores a plurality of sets of inverse gamma corrected pixel values. Also, the frame buffer stores, for each of the N-bit pixel values, a value that specifies a particular one of the plurality of sets of inverse gamma corrected pixel values for use in converting an associated one of the N-bit pixel values.
Inventors
- 👤 Sung Min Choi
- 👤 Leon Lumelsky
- 👤 Alan Wesley Peevers
- 👤 John Louis Pittas
- 👤 Calvin Bruce Swart
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-24 01:25
CPC Classifications
G; G09; G09G; G09G5/00; G09G5/02; G09G5/04; G09G1/00; G09G1/28; G09G1/285; G09G5/36; G09G5/39; G09G2320/00; G09G2320/02; G09G2320/0271; G09G2320/0276
Claims Analysis
Total Claims: 21
Claim 1
Independent Claim
153 words
An image display system comprising: a source of image pixel data wherein each pixel has an M-bit value within a non-linear range of values, said source means preferably comprising a camera having means for inverse gamma correcting a signal generated by said camera; first means, coupled to an output of said source, for converting each of said M-bit pixel values to an N-bit value within a linear range of values; storage means, having an input coupled to an output of said first converting means, for storing the N-bit pixel values; and second means, coupled to an output of said storage means, for converting N-bit pixel values output by said storage means to P-bit pixel values within a non-linear range of values prior to the application of said converted P-bit pixel data to a display means, wherein M preferably is greater than N and wherein P preferably is equal to or greater than N.
Claim 2
Dependent Claim
153 words
An image display system comprising: a source of image pixel data wherein each pixel has an M-bit value within a non-linear range of values, said source means preferably comprising a camera having means for inverse gamma correcting a signal generated by said camera; first means, coupled to an output of said source, for converting each of said M-bit pixel values to an N-bit value within a linear range of values; storage means, having an input coupled to an output of said first converting means, for storing the N-bit pixel values; and second means, coupled to an output of said storage means, for converting N-bit pixel values output by said storage means to P-bit pixel values within a non-linear range of values prior to the application of said converted P-bit pixel data to a display means, wherein M preferably is greater than N and wherein P preferably is equal to or greater than N.
Claim 3
Dependent Claim
37 words
Image display system as set forth in claim 1, wherein said first converting means operates in accordance with a gamma correction function and wherein said second converting means operates in accordance with an inverse gamma correction function.
Claim 4
Dependent Claim
48 words
Image display system as set forth in claim 1 or 2, wherein said first converting means includes a first memory means having address inputs coupled to said M-bit pixel values, said first memory means having a plurality of entries each of which stores a gamma corrected pixel value.
Claim 5
Dependent Claim
49 words
Image display system according to any one of the preceding claims, wherein said second converting means includes a second memory means having address inputs coupled to said N-bit pixel values, said second memory means having a plurality of entries each of which stores an inverse gamma corrected pixel value.
Claim 6
Dependent Claim
33 words
Image display system according to any one of the preceding claims, wherein said first memory means and said second memory means are each coupled to means for storing said corrected pixel values therein.
Claim 7
Dependent Claim
71 words
Image display system according to any one of the preceding claims, wherein said second memory means stores a plurality of sets of inverse gamma corrected pixel values, and wherein said storage means further stores, for each of the N-bit pixel values, a value that specifies a particular one of said plurality of sets of inverse gamma corrected pixel values for use in converting an associated one of said N-bit pixel values.
Claim 8
Dependent Claim
112 words
Image display system according to any one of the preceding claims, wherein P and N are related to an expression E = [S(e) 1/y /S] Y , where E is a video signal voltage and where y is a power function exponent, both of which are associated with the display means, and where the coefficient S satisfies the following relations: O = INT[P-1)(I/N-1) 1/y + 0.5] and I = !NT[(N-1)(0/P-1)Y + 0.5], where N = a number of linear input (I) levels, P = a number of gamma corrected output (O) levels, (I/N-1) and (O/P-1) are normalized input and output values, respectively, S = P-1, and INT is a truncating integer function.
Claim 9
Dependent Claim
46 words
Image display system according to any one of the preceding claims, wherein said source means further comprises an analog-to-digital conversion means having an input for receiving the inverse gamma corrected signal from said camera and an output for expressing the inverse gamma corrected signal with M-bits.
Claim 10
Dependent Claim
31 words
Image display system according to any one of the preceding claims and further including a digital-to-analog conversion means having a P-bit input coupled to an output of said second converting means.
Claim 11
Independent Claim
153 words
A method of operating an image display system, comprising the steps of: generating image pixel data wherein each pixel has an M-bit value within a non-linear range of values, said step of generating preferably comprising a step of inverse gamma correcting a signal generated by a camera and said step of generating preferably further comprising a step of analog-to-digital converting the inverse gamma corrected signal from the camera into a digital representation thereof having M-bits; converting each of the M-bit pixel values to an N-bit value within a linear range of values; storing the N-bit pixel values; converting N-bit pixel values output by said storage means to P-bit pixel values within a non-linear range of values; and said method preferably further comprising a step of applying the converted P-bit pixel data to a display means; wherein M preferably is greater than N and wherein P preferably is equal to or greater than N.
Claim 12
Independent Claim
153 words
A method of operating an image display system, comprising the steps of: generating image pixel data wherein each pixel has an M-bit value within a non-linear range of values, said step of generating preferably comprising a step of inverse gamma correcting a signal generated by a camera and said step of generating preferably further comprising a step of analog-to-digital converting the inverse gamma corrected signal from the camera into a digital representation thereof having M-bits; converting each of the M-bit pixel values to an N-bit value within a linear range of values; storing the N-bit pixel values; converting N-bit pixel values output by said storage means to P-bit pixel values within a non-linear range of values; and said method preferably further comprising a step of applying the converted P-bit pixel data to a display means; wherein M preferably is greater than N and wherein P preferably is equal to or greater than N.
Claim 13
Dependent Claim
64 words
Method as set forth in claim 10, wherein said first step of converting operates in accordance with a gamma correction function and wherein the second step of converting operates in accordance with an inverse gamma correction function and said second step of converting preferably converts the N-bit pixel values in accordance with one of a plurality of sets of inverse gamma corrected pixel values.
Claim 14
Dependent Claim
39 words
Method as set forth in claims 10 or 11, wherein the second step of converting includes a step of specifying, for each N-bit pixel value, a particular one of the plurality of sets of inverse gamma corrected pixel values.
Claim 15
Dependent Claim
111 words
Method according to any one of claims 10 to 12, wherein M and N are related to an expression E = [S(e) 1/y /S] Y , where E is a video signal voltage and where y is a power function exponent both of which are associated with the display means, and where the coefficient S satisfies the following relations: O = INT[P-1)(I/N-1) 1/y + 0.5] and I = !NT[(N-1)(0/P-1)Y + 0.5], where N = a number of linear input (I) levels, P = a number of gamma corrected output (O) levels, (I/N-1) and (O/P-1) are normalized input and output values, respectively, S = P-1, and INT is a truncating integer function.
Claim 16
Dependent Claim
23 words
Method according to any one of claims 10 to 13 and further including a step of digital-to-analog converting the P-bit bit pixel values.
Claim 17
Dependent Claim
205 words
An image display system comprising: a source of inverse gamma corrected image pixel data wherein each pixel is expressed with M-bits, said gamma correcting means preferably comprising a first look-up table means having address inputs coupled to said M-bit pixel values and wherein said inverse gamma correcting means preferably comprises a second look-up table means having address inputs coupled to said N-bit pixel values; means, coupled to an output of said source, for gamma correcting each of said M-bit pixel values to an N-bit value within a linear range of values; frame buffer means, having an input coupled to an output of said first converting means, for storing the gamma converted N-bit pixel values, said frame buffer means being preferably coupled to a host means operable for storing N-bit image pixel data therein; means, coupled to an output of said frame buffer means, for inverse gamma correcting N-bit pixel values output by said frame buffer means to P-bit pixel values; and means, coupled to an output of said inverse gamma correcting means, for converting the P-bit pixel data to an analog voltage for driving a CRT-display means, wherein M preferably is greater than N and wherein P preferably is equal to or greater than N.
Claim 18
Dependent Claim
205 words
An image display system comprising: a source of inverse gamma corrected image pixel data wherein each pixel is expressed with M-bits, said gamma correcting means preferably comprising a first look-up table means having address inputs coupled to said M-bit pixel values and wherein said inverse gamma correcting means preferably comprises a second look-up table means having address inputs coupled to said N-bit pixel values; means, coupled to an output of said source, for gamma correcting each of said M-bit pixel values to an N-bit value within a linear range of values; frame buffer means, having an input coupled to an output of said first converting means, for storing the gamma converted N-bit pixel values, said frame buffer means being preferably coupled to a host means operable for storing N-bit image pixel data therein; means, coupled to an output of said frame buffer means, for inverse gamma correcting N-bit pixel values output by said frame buffer means to P-bit pixel values; and means, coupled to an output of said inverse gamma correcting means, for converting the P-bit pixel data to an analog voltage for driving a CRT-display means, wherein M preferably is greater than N and wherein P preferably is equal to or greater than N.
Claim 19
Dependent Claim
41 words
Image display system as set forth in claim 15, wherein said first look-up table means and said second look-up table means are each coupled to a host means operable for storing gamma correction values and inverse gamma correction values, respectively, therein.
Claim 20
Dependent Claim
74 words
Image display system according to claim 15 or 16, wherein said second look-up table means stores a plurality of sets of inverse gamma corrected pixel values, and wherein said frame buffer means further stores, for each of the N-bit pixel values, a value expressed with W-bits that specifies a particular one of said plurality of sets of inverse gamma corrected pixel values for use in converting an associated one of said N-bit pixel values.
Claim 21
Dependent Claim
38 words
Image display system according to any one of claims 15 to 17, wherein said frame buffer means is comprised of xN + W-bit memory planes, where x is a number of color signal inputs to said CRT-display means.
References Cited (Backward Citations)
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