Noise quantity measuring apparatus

Abstract

The present invention provides a noise quantity measuring apparatus adaptable to a video input signal subjected to automatic gain control. A luminance determination circuit compares luminance levels of respective pixels constituting a video input signal VIN and a predetermined threshold value for every arbitrary area Ai. If even one of the luminance levels exceeds the threshold value, then the luminance determination circuit outputs a detection signal DET to the corresponding area Ai. Sums SUMi of luminance level differences developed every plural arbitrary areas Ai, which are outputted from an integration circuit, are supplied to a selection circuit, where they are compared with an output signal OUT. Thereafter, each smaller value is supplied to a register. The register holds the output of the selection circuit in accordance with a latch signal LAT supplied from a pulse generator. On the other hand, when the detection signal DET is outputted, the latch signal LAT outputted from the pulse generator is stopped. Thus, the sum of the luminance level differences with respect to each area having pixels whose luminance levels exceed the threshold value, is ignored and eliminated from an output signal OUT indicative of the quantity of noise.