Method and apparatus for deriving a color controlled video mixer

Details Method and apparatus for deriving a color controlled video mixer Method and apparatus for deriving a color controlled video mixer

1990-09-12

1992-08-18

Goody, James J.

Facsimile and static presentation processing

Static presentation processing

Attribute control

358183, 358178, H04N 974, H04N 5262

Patent

active

051404095

ABSTRACT:
For deriving a keying signal for a video mixer from a video pattern signal which may be derived by reference to the presence of a selected color in one of the video signals to be mixed, the level-shift voltage added to the video signal for producing the clipped video pattern signal, instead of being constant, is derived from at least one amplitude envelope signal produced from the video signal in order to overcome effects of non-uniform lighting or shadow effects in the picture that contains a selected color. The clip voltage is about half of the amplitude envelope signal. Preferably, both positive and negative amplitude envelope signals are generated and the level-shift voltage is then the mean value of the voltages contemporaneously represented by the envelope signals. The envelope signals are stored for a picture field interval before being used to generate the level-shift voltage.

REFERENCES:
patent: 4051520 (1977-09-01), Davidse
patent: 4758892 (1988-07-01), Bloomfield
patent: 4947255 (1990-08-01), Jackson et al.
patent: 4963977 (1990-10-01), Jackson et al.
patent: 4994905 (1991-02-01), Lee et al.
SMPTE Journal, Mar. 1977, vol. 86, "Chroma-Key System Insensitive to Variations of the Background Illumination" pp. 140-143.

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