The ratio of the size of data in the non-compressed digital video signal to the compressed version. Modern compression techniques start with component television signals but a variety of sampling systems are used, 4:2:2 (‘Studio’ MPEG-2), 4:2:0 (MPEG-2), 4:1:1 (DVCPRO), etc. The compression ratio should not be used as the only method to assess the quality of a compressed signal. For a given technique, greater compression can be expected to result in worse quality but different techniques give widely differing quality of results for the same compression ratio. The only sure method of judgement is to make a very close inspection of the resulting pictures – where appropriate, re-assessing their quality after onward video processing.