Apparatus and a method for limiting gain in a digital gamma corr

Details Apparatus and a method for limiting gain in a digital gamma corr Apparatus and a method for limiting gain in a digital gamma corr

1992-06-19

1993-10-19

Kostak, Victor R.

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

358 32, H04N 5202

Patent

active

052550931

ABSTRACT:
A method and apparatus for reducing the maximum gain applied to a video signal during gamma correction are disclosed. A gamma exponent value, a black level, white level, and a desired maximum gain value are selected. A count of possible input signal values is determined. A modified black level is set equal to the desired black level. A gain limit value for the gamma correcting transfer function is calculated, and the smallest input signal for which the applied gain is less than or equal to the gain limit is determined. A black level correction factor is calculated. The modified black level is increased by the black level correction factor, and a determination is made whether the black level correction factor has decreased to less than a predetermined threshold value. The gamma correction function is recalculated and further black level corrections are added until the correction threshold is reached. The final transfer function increases linearly and has a gain equal to the gain limit value for video signal values near the desired black level. The gamma function increases non-linearly at a decreasing rate near the white level.

REFERENCES:
patent: 4799106 (1989-01-01), Moore et al.
patent: 4805013 (1989-02-01), Dei et al.
patent: 5132796 (1992-07-01), Topper et al.

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