Compensation of brightness and colour homogeneity of the background image in linear image mixing

摘要

Control signal Ec is generated (18) proportional to luminance of a foreground scene comprising a subject (10) selectively before a blue backing (17). Ec is corrected for luminance non-uniformity (Fig. 3) by multiplying (31) live Ec with the subject present by the reciprocal (29) of stored (30) Ec without the subject such that the corrected control signal (LEc) is unity wherever the foreground video signal represents the backing (17). Color correction (Fig. 6) corrects, for example, the blue video signal to a predetermined ideal value (36) where the foreground signal represents the backing (17) and may be applied to all three of the RGB signals using one (Fig. 7), two (Fig. 8A) or three (Fig. 8) memories. IMAGE