GB1208807A - Improvements in television picture sources - Google Patents

Abstract

1,208,807. Television. BRITISH BROADCASTING CORP. 7 July, 1969 [25 Sept., 1968], No. 45606/68. Heading H4F. To compensate for light scattered within the picture source and unwanted light generated within the source which results in a false distribution of light in the reproduced image, i.e. flare, a signal proportional to the video signal integrated over a field or picture period is added to the video signal. When a film is scanned by a flying-spot scanner the distortion due to flare is caused by stray light appearing on the phosphor of the tube displaying the raster which is imaged in the plane of the scanned film. This uniformly distributed flare results in a displacement of the true black level in the video signal. Flare caused by abrupt changes of picture content due to editing the filmed material is also compensated. As shown, the input video signal is blacklevel clamped 13 and fed to integrator 14 which is reset during every or every other field blanking interval. The resulting integrated field or picture is retained in a sample and hold circuit 15 and applied to a switch 16. Preferably, switch 16 is closed once during each line blanking interval, the resulting pulses being added 17 to the input video signal to produce the output 18 on which subsequent black-level clamps will act to restore true black level and hence eliminate or at least reduce flare. As shown, the correction formed during one integration period is applied to the next following integration period. To avoid this " overshoot " the input video signal applied to adder 17 may be delayed for one integration period. Switch 16 may be closed during the line period instead of the line blanking period, the resulting pulses being inverted. When compensating a colour picture source each colour camera output may be independently compensated or a common correction signal may be utilized.