JPS6439184A - Enhancing circuit - Google Patents

Abstract

PURPOSE:To execute an enhancement without a malfunction and an S/N deterioration at the flatted part of a signal waveform by detecting the amplitude change of a luminance signal and subtracting a secondary differential signal of a color difference signal from the original color difference signal during only the detection period. CONSTITUTION:A band control signal (c) by passing an input luminance signal (a) through an LPF2 is obtained, the signal is differentiated at a differentiation circuit 3 and a signal (d) is obtained. When the signal (d) is present, the amplitude of the signal (a) is changed and the color difference signal is also changed. A signal (e) detecting the signal (d) is supplied to a comparator 5 in order that an output (f) is not generated at a minute level by setting a threshold level. On the other hand, the time of signals (g) and (c) is set by passing an input signal (b) through a delay circuit 7. The signal (g) is inputted to a secondary differentiation circuit 8 to obtain the secondary differential signal (h). A switch circuit 10 is switched by the output (f), the circuit 10 is turned on only the period when the luminance signal is changed, an enhanced color difference signal (j) is obtained by subtracting a passing signal (i) from the signal (g) and the signal is outputted from an output terminal 11.