Image analysis – Color image processing – Color correction
Reexamination Certificate
1998-11-20
2001-02-13
Tadayon, Bijan (Department: 2721)
Image analysis
Color image processing
Color correction
C382S173000
Reexamination Certificate
active
06188788
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention pertains in general to video decoders and, more particularly, to a video decoder operating in a YUV format with automatic color saturation control.
BACKGROUND OF THE INVENTION
In order to maintain a constant color level in the color output of a digital video decoder, automatic color saturation control is required. The goal of this automatic color saturation control is to maintain a constant color level as the strength of the signal varies over time. In general, color saturation control utilizes the amplitude of the color burst as a benchmark wherein the amplitude of the burst is measured and then compared with an ideal value. The ratio of the ideal burst amplitude to the measured burst amplitude is then computed and multiplied by the nominal cb and cr factors to produce multiplication factors, these factors being the color difference signals in a YCrCb color format. These multiplication factors are then applied to the demodulated U and V color difference signals within the video decoder in the YUV color format.
When implementing the above-noted algorithm, a number of divisions and multiplication operations are required to define the ratio. Typically, these division and multiplication operations are implemented by initially looking up an approximate value for the reciprocal of the measured value in a lookup table, and then refining it with the Newton Raphson recursive relation to improve the accuracy. This processing requires not only the use of a lookup table, but also multiplications which consumes a large portion of a simple microprocessor's throughput. The refine process can be eliminated at the expense of a course approximation. The lookup process itself involves a large amount of code which examines the measured burst amplitude and determines a range bin corresponding to an approximation to the ratio. The ratio must then be multiplied times the nominal cr and cb factors.
SUMMARY OF THE INVENTION
The present invention disclosed and claimed herein comprises a method and apparatus for controlling the color level in the color output of a video decoder. The color difference signals U and V associated with a YUV color format are first derived. The actual burst amplitude of the composite video color signal is then measured and compared to an ideal burst amplitude by determining the ratio of the measured burst amplitude to the ideal burst amplitude. This determined ratio is the scale factor which is determined utilizing a recursive relationship that requires only addition and subtraction. Nominal correction factors for the U and V color difference signals are then provided which represent correction factors therefor under normal conditions. These nominal correction factors are scaled with the scale factor utilizing a recursive relationship that represents the respective first and second nominal correction factors divided by the scale factor. This recursive relationship also utilizes only addition and subtraction operations to provide on the output thereof respective scaled first and second correction factors. The color difference signals are then scaled with the scaled correction factors.
REFERENCES:
patent: 3716663 (1973-02-01), Bolger
patent: 4463371 (1984-07-01), Lewis, Jr.
patent: 4635102 (1987-01-01), Bolger
patent: 5493339 (1996-02-01), Birch et al.
patent: 5585929 (1996-12-01), Young et al.
Chang Weider Peter
Renner Karl
Alavi Amir
Brady III Wade James
Stewart Alan K.
Tadayon Bijan
Telecky , Jr. Frederick J.
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