| 摘要 |
PURPOSE:To improve an S/N of chrominance signal of a low luminance naturally and without a sense of incongruity by using a digital circuit and controlling dynamically a band of the chroma signal in accordance with the level of a luminance signal. CONSTITUTION:A chroma signal CA is quantitized by an A/D converter 50, goes to be a digital chroma signal CD and is inputted to a variable band two-dimensional digital filter 52. On the other hand, a luminance signal YA is quantitized by the same clock at a A/D converter 51 and goes to be a digital luminance signal YD. A threshold TH is set from the external part to the variable band two-dimensional digital filter 52, and a logic Lo is set beforehand. The level of a digital luminance signal YD, is decided by a threshold level TH at a level deciding circuit, the higher the level is, the more the delay output is selected, and the lower the level is, the more the filter output is selected. Thus, the lower the level of the luminance signal YA is, the narrower the band of the chroma signal is, and an S/N is improved.
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