The Digital Fact Book - Quantel

CCompression ratioThe ratio of the amount of data in the non-compressed digital video signal to the compressedversion. Modern compression techniques start with component television signals buta variety of sampling systems are used, 4:2:2 (‘Studio’ MPEG-2), 4:2:0 (MPEG-2), 4:1:1(NTSC, DVCPRO), etc. The compression ratio should not be used as the only method toassess the quality of a compressed signal. For a given technique, greater compression canbe expected to result in lower picture quality but different techniques give widely differingquality of results for the same compression ratio. The more modern technologies, MPEG-4(H 264), VC-1, and JPEG 2000 are more efficient than MPEG-2. The only sure method ofjudgment is to make a very close inspection of the resulting pictures – where appropriate,re-assessing their quality after onward video processing.See also: Concatenation, DV, ETSI, JPEG, JPEG 2000, MPEGConcatenationThe linking together of systems in a linear manner. In digital television this often refersto the concatenation of compression systems which is a subject of concern becauseany compression beyond about 2:1 results in the removal of information that cannot berecovered. As the use of compression increases, so too does the likelihood that materialwill undergo a number of compressions between acquisition and transmission. Althoughthe effects of one compression cycle might not be very noticeable, the impact of multipledecompressions and recompressions – with the material returned to baseband in between– can cause considerable damage. The damage is likely to be greatest where differentcompression schemes are concatenated in a particular signal path.Video Rushes Edit TransmissionPlayoutMPEG-2EncoderTransmitterHomeBandwidth46