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[filmscanners] RE: JPEG2000/PNG on PS7.0 and PSP8.0
>-----Original Message-----
>From: filmscanners_owner@halftone.co.uk
>[mailto:filmscanners_owner@halftone.co.uk]On Behalf Of Julian Robinson
>your figures for the compression ratios fo JPEG2000 seem very low
>to me, I am interested to know why. I get more towards 2:1 mostly, with
>the worst figure ever around 15% and an average around 40%. You get an
>average around 12%. Perhaps my images are lacking detail, or are yours
>especially grainy? Not criticising, just would like to have a handle on all
>this.
One other possibility is that he works with 16-bit TIFFs and you with 8-bit
TIFFs. If you go beyond 8 bits the compression ratio falls pretty fast. As a
matter of fact, jpeg2000 even allows to bypass parts of the algorithm after
5 bitplanes because compression is not very significant anymore (because
there isn't much correlation anymore). Therefore, for images with many
bitplanes it makes sense to use a bigger compression ratio as not that much
is lost.
Robert
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