| 摘要 |
PURPOSE: To prevent increase of a quantization noise by providing a digital low frequency filter for filtering a block subjected to follow a discrete cosine transformation(DCT) and subjecting a buffer to follow so as to lower the upper frequency cutoff when the filled amount of the buffer increases. CONSTITUTION: The digital low frequency filter 12 is inserted below a switch 31 which is controlled by a selector 2, and the output SS of the filter 12 is added to a discrete cosine transformation circuit 3. Then, a signal block SB (i.nner field) and a difference block SE (i,nterframe) are added to the two inputs of the switch 31 and the two inputs of the selector 2, and the filter 12 attenuates high frequency in the signals SB and SE to be converted. Then, the level of a corresponding DCT coefficient is reduced, and the filter characteristi,c i.e. its cutoff frequency is controlled by a quantizati.on resolution control signal in order to lower the cutoff frequency corresponding to the filled amount of the buffer 10. Thus, increase of the quantization noise of the DCT coefficient is prevented. |
