Variable chrominance filtering for encoding television signals

Details Variable chrominance filtering for encoding television signals Variable chrominance filtering for encoding television signals

1990-12-26

1992-09-22

Chin, Tommy P.

Facsimile and static presentation processing

Static presentation processing

Attribute control

358 31, H04N 978, H04N 1114

Patent

active

051502038

ABSTRACT:
A chrominance filtering system reduces chrominance detail when sufficient luminance detail is present, but limits how much chrominance detail is reduced when insufficient luminance detail is present. The chrominance input signal is applied to a high pass filter and a suitable delay circuit. The output of the high pass filter, C.sub.hp, is a signal indicative of chrominance detail. It is applied to the input of a bipolar clipping circuit that also receives a control signal, .vertline.Y.sub.hp '.vertline..sub.clipped indicative of luminance detail. The control signal is derived by high pass filtering, rectifying and low pass filtering the luminance signal to produce a signal, .vertline.Y.sub.hp .vertline., that is absolute value of high pass filtered luminance activity. This signal is then scaled by multiplication by a first constant and then offset by addition to a second constant to produce .vertline.Y.sub.hp '.vertline.. .vertline.Y.sub.hp '.vertline. is then clipped to be between a minimum and a maximum value to produce the control signal .vertline.Y.sub.hp '.vertline..sub.clipped. The bipolar clipping circuit constrains C.sub.hp to produce C.sub.hpc according to the following relationships: If C.sub.hp is > or =0, then C.sub.hpc is > or = to .vertline.Y.sub.hp '.vertline..sub.clipped ; or if C.sub.hp is <0, then C.sub.hpc is < or = to -.vertline.Y.sub.hp '.vertline..sub.clipped. The first and second constants and the minimum and maximum values are optimized empirically.

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