Method and apparatus for correcting video color signals

Facsimile and static presentation processing – Static presentation processing – Attribute control

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358 27, 358 28, 358 80, H04N 975, H04N 968

Patent

active

049548816

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

This invention relates to correcting video color signals and, more particularly, to a method and apparatus for precisely isolating video color signals for selective color correction.
In video color recording, the images are represented by either of two sets of signals. One signal set is red/green/blue. The other signal set is luminance (Y) and color difference, i.e. red minus luminance (R-Y) and blue minus luminance (B-Y).
In the course of production of television and video color recordings, it is sometimes desirable to correct selectively the colors of the subject images. Many years ago Monahan et al. disclosed a non-linear matrixing device for color correction in U.S. Pat. No. 3,558,806. This matrixing device operates upon the red/green/blue signals to permit independent adjustment of the hue and saturation of the three primary colors, red, green, and blue, and the secondary colors, cyan, yellow, and magenta. When an object made up of more than one color is to be color corrected, a coordinated adjustment of both colors is required.
Recently, Korman disclosed in U.S. Pat. No. 4,525,736 color modification apparatus which operates upon the color difference signals known as I and Q, rather than the primary and secondary color signals. The color signals to be corrected are selected by limit circuits which determine when the difference signals lie between prescribed boundaries in the chrominance plane. These boundaries define rectangular regions in the chrominance plane which do not correspond to the polar coordinate color corrections actually made by the colorist. As a result, the colorist may encounter difficulty in selecting the signals to be color corrected.


SUMMARY OF THE INVENTION

According to the invention, video signal color correction is accomplished by selecting for color correction areas of the chrominance plane defining sectors in polar coordinants. Both the angle and the width of the sectors can be changed to select precisely the desired signals for color correction. Specifically, video component color difference signals which only lie within a fixed hue sector are transmitted from an input to an output. Responsive to a first control signal, the difference signals are rotated through an angle which corresponds to a selected hue sector relative to the fixed hue sector in which the component color signals are to be corrected. The rotated difference signals are applied to the input to produce at the output an isolated color signal only when the difference signals lie within the selected hue sector. The width of the fixed hue sector is reduced responsive to a second control signal. Thus, the first and second control signals permit selection of the angle and the width of the sector in which the difference signals are to be color corrected.


BRIEF DESCRIPTION OF THE DRAWINGS

The features of a specific embodiment of the best mode contemplated of carrying out the invention are illustrated in the drawings in which:
FIG. 1 is a schematic block diagram of a color correction system incorporating principles of the invention;
FIG. 2 is a schematic block diagram of the multi-channel color correction circuitry represented in FIG. 1;
FIG. 3 is a schematic block diagram of one channel of the color correction circuitry represented in FIG. 2;
FIG. 4 is a schematic block diagram of the angular hue rotation circuitry represented in FIG. 3;
FIG. 5 is a schematic block diagram of the angular hue spread circuitry represented in FIG. 3; FIG. 6 is a diagram of the chrominance plane with the difference signals, R-Y and B-Y, as coordinates; FIG. 7 is a diagram of sine and cosine wave forms used to describe the operation of the invention;
FIG. 8 is a collection of diagrams representing the component color signals for a standard six color bar chart
FIGS. 9A, 9B and 9C are diagrams representing the output signals of the angular hue rotation circuitry of FIG. 3 for an expanded thirty color bar chart;
FIGS. 10A, 10B and 10C are diagrams representing the signals generated by the angular hue spread

REFERENCES:
patent: 3255305 (1966-06-01), Chatten
patent: 3558806 (1971-01-01), Monahan
patent: 3678182 (1972-07-01), Boxman et al.
patent: 3959813 (1976-05-01), Legler
patent: 4051520 (1977-09-01), Davidse et al.
patent: 4109278 (1978-08-01), Mendrala et al.
patent: 4410908 (1983-10-01), Belmares-Sarabia et al.
patent: 4500919 (1985-02-01), Schreiber
patent: 4525736 (1985-06-01), Korman
patent: 4533938 (1985-08-01), Hurst
patent: 4763186 (1988-08-01), Belmares-Sarabia et al.
patent: 4811084 (1989-03-01), Belmares-Sarabia et al.
patent: 4862251 (1989-08-01), Belmares-Sarabia et al.
Monahan and Dischert, Journal of the SMPTE, Sep. 1969, pp. 696-700, Title: Color Correction Techniques for Television Cameras.

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