JPS6416115A - Slew rate limiting filter - Google Patents

Abstract

PURPOSE:To prevent the occurrence of color deviation, color blur, or the like by providing a detecting means which outputs a detection signal corresponding to the slew rate of an input signal or the magnitude of a high frequency component, a filter means which permits a prescribed low frequency component to pass through, and a mixing means which controls a mixture ratio of the output signal of the filter means to the input signal in accordance with the detection signal. CONSTITUTION:A high band component of the video signal is extracted by a high-pass filter (HPF) 2. An output signal 2a of the HPF 2 is introduced to an absolute value circuit 3 to convert the negative polarity component to a positive polarity component. An output signal 3a of the absolute value circuit 3 is large mainly in the large-amplitude outline part of a picture. A low pass filter (LPF) 4 has such slow cut-off characteristic that ringing is inconspicuous even if the band is limited to a required band. An output signal 4a and an output signal 5a of a delay line 5 corresponding to the extent of delay of the LPF 4 are switched in accordance with the output signal of the absolute value circuit 3. Thus, the signal is obtained where only the large-amplitude outline part of the picture is subjected to slew rate limitation by the LPF 4.