Method and apparatus for applying gamma predistortion to a color image signal
First Claim
1. Apparatus for producing, from samples of substantially linear video components of a color image comprising a linear luminance component and linear first and second chrominance components, samples of corresponding gamma-predistorted video components, comprising:
- a. an inverse gamma function generator which supplies, from a linear luminance sample Y* obtained by sampling the linear luminance component, a gamma-predistorted luminance value Y'"'"', according to the relationship Y'"'"'=(Y'"'"')1/γ
, where γ
is the gamma of a display to be driven by said gamma-predistorted video components; and
b. for at least one chrominance component, a corresponding chrominance lookup table addressed by both the value of the linear luminance sample and the value of the chrominance component and supplying a substantially gamma-predistorted chrominance component value.
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Abstract
A system and method for generating gamma-predistorted video signals. A close approximation to the ideal gamma predistorted values of Y, Cr and Cb video signal components are generated from linear camera or computer output signals using at most a single matrix multiplication, one channel of inverse gamma function generation (on the luminance component) and two table look up operations. The linear luminance value is predistorted by an inverse gamma function. If they are not available from the video source, a matrix multiplication is used to generate linear luminance and chrominance signals. The linear chrominance signals are then adjusted for their dependence on luminance using a two-dimensional table look-up. The lookup table(s) is (are) addressed by the linear luminance value and by each of the linear chrominance values to produce gamma-predistorted Cr and Cb signals from the tables.
58 Citations
24 Claims
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1. Apparatus for producing, from samples of substantially linear video components of a color image comprising a linear luminance component and linear first and second chrominance components, samples of corresponding gamma-predistorted video components, comprising:
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a. an inverse gamma function generator which supplies, from a linear luminance sample Y* obtained by sampling the linear luminance component, a gamma-predistorted luminance value Y'"'"', according to the relationship Y'"'"'=(Y'"'"')1/γ
, where γ
is the gamma of a display to be driven by said gamma-predistorted video components; andb. for at least one chrominance component, a corresponding chrominance lookup table addressed by both the value of the linear luminance sample and the value of the chrominance component and supplying a substantially gamma-predistorted chrominance component value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 19, 20, 21, 22, 23, 24)
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8. Apparatus for producing from substantially linear video components comprising a linear luminance component and linear, first and second chrominance components, corresponding gamma-predistorted video components, comprising:
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a first lookup table addressed by the value of a sample of the linear luminance component and a sample of the first chrominance component and supplying a substantially gamma-predistorted first chrominance component value and a substantially gamma-predistorted luminance value; a second lookup table addressed by the value of a sample of the luminance component and the value of a sample of the second chrominance component and supplying a substantially gamma-predistorted second chrominance component value and a substantially gamma-predistorted luminance value; and a multiplexer connected to receive the gamma-predistorted luminance values from the first and second lookup tables and to alternatingly select the gamma-predistorted luminance value from the first lookup table and the gamma, predistorted luminance value from the second lookup table.
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9. A method of producing, from substantially linear video components comprising a linear luminance component and first and second chrominance components, corresponding gamma-predistorted video components, comprising the steps of:
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a. predistorting the linear luminance component, Y*, by an inverse gamma function, to produce a gamma-predistorted luminance component, Y'"'"'; b. addressing a first two-dimensional lookup table in a first dimension by the linear luminance component, Y*, and in a second dimension by the first chrominance component, to provide a gamma-predistorted first chrominance component; and c. addressing a second two-dimensional lookup table in a first dimension by the linear luminance component, Y*, and in a second dimension by the second chrominance component, to provide a gamma-predistorted second chrominance component. - View Dependent Claims (10)
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11. A method of producing, from substantially linear video components comprising a linear luminance component and first and second chrominance components, corresponding gamma-predistorted video components, comprising the steps of:
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a. predistorting the linear luminance component, Y'"'"', by an inverse gamma function, to produce a gamma-predistorted luminance component, Y'"'"'; and b. addressing a two-dimensional lookup table 1. at first instances, in a first dimension by a sample of the linear luminance component Y'"'"', and in a second dimension by a sample of the first chrominance component, to provide a gamma-predistorted first chrominance component; and 2. at second instances, in a first dimension by a sample of the linear luminance component, Y*, and in a second dimension by a sample of the second chrominance component to provide a gamma-predistorted second chrominance component. - View Dependent Claims (12)
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13. A method of producing from substantially linear video components comprising a linear luminance component and first and second chrominance components corresponding gamma-predistorted video components, comprising the steps of:
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a. addressing a first lookup table by the value of the linear luminance component and the first chrominance component and supplying a substantially gamma-predistorted first chrominance component value and a substantially gamma-predistorted luminance value; b. addressing a second lookup table by the value of the linear luminance and the second chrominance component and supplying a substantially gamma-predistorted second chrominance component value and a substantially gamma-predistorted luminance value; and c. interleaving the gamma-predistorted luminance values from the first and second lookup tables. - View Dependent Claims (14, 15, 16, 17, 18)
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Specification