Abstract: The present invention relates to filtering an interlaced input digital signal containing fields of chrominance information preparatory to converting the format of the signal by means of a downsampling conversion from a 4:2:2 format to a 4:2:0 format. In the invention, the input signal is applied to a delay circuit to derive samples of the input signal representing spatially separated elements from each chrominance field where the spatial separation is of one line. The magnitudes of the samples are compared relative to one another to identify frequencies which fall within different high and low frequency ranges. An adaptive filter has a plurality of frequency responses corresponding to the frequency ranges and a frequency response is selected in accordance with the identified frequency range of the input signal samples.

Abstract: Edge Enhanced Noise Reduction (EENR) is a frequency dependent instantaneous compander system. It is applied only in the encoder both to Chrominance and luminance, and is best placed after the horizontal and vertical down sampling filters in the pre-processing stages of an encoder (not shown per se). High frequency, low level information (mainly noise) are reduced significantly in amplitude. In particular, EENR is designed to preserve edge details. In addition, a vertical recursive filter can be used to prevent low level vertical information from being removed by the system. This is partially useful in the luminance path. High level, high frequency components remain virtually unaffected. The system is `transparent` to low frequency information. EENR has been designed to work in conjunction with MPEG encoding presented with source material which is slightly noisy and where the transmission bit rate is being constrained.