[Tig] video compression: lossless? (JPEG2000) (Rob Lingelbach)

Richard Kirk richard at filmlight.ltd.uk
Mon Oct 19 08:46:18 BST 2009


You can usually get about 2x compression with lossless processes. 
Two-and-a bit, maybe. Beyond that, you are limited by the noise level on 
your signal. Suppose you have an 8-bit video signal, and something like 
32:1 signal to noise (+/-4: not an unreasonable figure). This will mean 
the bottom three bits will essentially be unpredictable noise. If you 
are transmitting a flat screen of grey so there is no picture 
information whatever, you would expect to get only 8/3x compression = 
2.67. If you have more bits then you have to have a greater signal to 
noise ratio to get the same compression ratio. This limit applies to any 
lossless compression systems. The only exceptions are artificial, 
noiseless images such as text or rendered images.

A bit more than 2x compression may not sound much, but it is more than 
YCrCb encoding, and it does a lot less damage.

Cheers.
Richard Kirk

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