GB1336498A - Television shot-change detector - Google Patents

Abstract

1336498 Television BRITISH BROADCASTING CORP 5 Sept 1972 [13 Sept 1971] 42574/71 Heading H4F Scene changes, known as shot-changes, in a live or recorded television signal are detected by delaying, 16, the signal by one (or more) field periods, comparing, e.g. subtracting, 18, the delayed and undelayed signals, full wave rectifying, 20, the resultant of the comparison, integrating, 22, the rectified signal over one or more field periods, and detecting, 24, when the resultant of the integration reaches a given value, e.g. using a Schmitt trigger type threshold circuit. The input signal is preferably fed via a low-pass filter 12 and a level control amplifier 14 (Fig. 2, not shown) which maintains the mean amplitude of the signal at a pre-set value to the delay 16 and subtractor 18. The level control amplifier is arranged to take many fields to correct any change in signal level, so that rapid changes in amplitude between fields due to shot changes are not reduced by the operation of the level control and the detector 24 is therefore equally sensitive to signal changes in scenes of high or low mean luminance. The television signal may be converted to digital form, e.g. using delta modulation, the delay device being a shift register (Fig. 3, not shown). The detector 24 instead of detecting when the integrated signal reaches a given fixed magnitude may include an analogue bucket-brigade delay device and a comparator which detect when the integrated signal for any one integration period (e.g. two fields) exceeds its value for one or more (e.g. two) of each of the previous and following integration periods by a given amount or factor (Fig. 4, not shown).