US4568978A
Expired / Lapsed
US
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Method of a circuit arrangement for producing a gamma corrected video signal
Assignee: US Philips Corp
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Filing: 1983-06-15
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Granted: 1986-02-04
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Expires: 2003-06-15
Abstract
Abstract A gamma correction factor is applied to a video signal without need of the normally used multiplier by forming the logarithm of the logarithm of the video signal and algebraically adding this signal to a second signal representing the logarithm of the correction factor. The anti-log of the anti-log of the resulting signal constitutes the gamma corrected signal. Analog and digital implementations of the circuitry are illustrated.
Inventors
- 👤 Ian S. Cosh
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 07:12
CPC Classifications
H; H04; H04N; H04N5/00; H04N5/14; H04N5/20; H04N5/202
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
84 words
A method of correcting a video signal by a gamma correction factor, comprising the steps of: forming a logarithm of a logarithm of said video signal, thereby creating a first signal; forming a logarithm of said correction factor, thereby creating a second signal; algebraically adding said first and second signals, thereby forming a third signal; and forming an anti-logarithm of an anti-logarithm of said third signal, thereby creating a fourth signal, said fourth signal constituting said video signal corrected by said gamma correction factor.
Claim 2
Independent Claim
84 words
A method of correcting a video signal by a gamma correction factor, comprising the steps of: forming a logarithm of a logarithm of said video signal, thereby creating a first signal; forming a logarithm of said correction factor, thereby creating a second signal; algebraically adding said first and second signals, thereby forming a third signal; and forming an anti-logarithm of an anti-logarithm of said third signal, thereby creating a fourth signal, said fourth signal constituting said video signal corrected by said gamma correction factor.
Claim 3
Dependent Claim
73 words
A method as claimed in claim 1, wherein said first signal (P) is equal to log B (-log A V i ) where V i is said video signal, wherein said second signal (Q) is equal to log B G where G is said correction factor, wherein said third signal (R) is equal to P±Q, and said fourth signal is equal to A exp (-B exp R), where A and B are constants.
Claim 4
Dependent Claim
37 words
A method as claimed in claim 2, in which the video signal is in digital form and A is equal to 2 n where n is the number of bits defining the amplitude of the video signal.
Claim 5
Independent Claim
18 words
A method as claimed in claims 2 or 3 wherein B=10 x where x=log 10 [-log A (A=1/A)].
Claim 6
Dependent Claim
108 words
A circuit arrangement for correcting a video signal applied to an input thereof by a gamma correction factor comprising means for forming a first signal representative of a logarithm of a logarithm of said video signal, means for forming a second signal representative of a logarithm of said correction factor, means for forming a third signal representative of the algebraic sum of said first and second signals, means for forming a fourth signal representative of an anti-logarithm of an anti-logarithm of said third signal, and means for feeding said fourth signal to an output of the circuit arrangement as said video signal corrected by said gamma correction factor.
Claim 7
Dependent Claim
108 words
A circuit arrangement for correcting a video signal applied to an input thereof by a gamma correction factor comprising means for forming a first signal representative of a logarithm of a logarithm of said video signal, means for forming a second signal representative of a logarithm of said correction factor, means for forming a third signal representative of the algebraic sum of said first and second signals, means for forming a fourth signal representative of an anti-logarithm of an anti-logarithm of said third signal, and means for feeding said fourth signal to an output of the circuit arrangement as said video signal corrected by said gamma correction factor.
Claim 8
Dependent Claim
71 words
A circuit arrangement as claimed in claim 5, wherein said first signal (P) is equal to log B (-log A V i ) where V i is said video signal, said second signal is equal to log B G where G is said correction factor, said third signal (R) is equal to P±Q, and said fourth signal is equal to A exp (-B exp R), where A and B are constants.
Claim 9
Dependent Claim
33 words
A circuit arrangement as claimed in claim 5 or claim 6, in which said video signal is in digital form, and wherein the first, second and third means comprise programmed digital memory devices.
Claim 10
Dependent Claim
11 words
A circuit arrangement as claimed in claim 6, in which A=1024.
Claim 11
Dependent Claim
18 words
A circuit arrangement as claimed in claim 6, in which B=10 x where x=[log 10 (-log A (A-1/A)].
Claim 12
Dependent Claim
25 words
A circuit arrangement as claimed in claim 5, in which the resolution of said gamma corrected signal is four times that of said video signal.
References Cited (Backward Citations)
US4394688A
Cited
US4499494A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1989-02-03 | 1989-08-05 | 1990-02-04 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1993-02-03 | 1993-08-05 | 1994-02-04 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1997-02-03 | 1997-08-05 | 1998-02-04 | $7700.00 | Window Closed / Lapsed |