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June 2011
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2011.06.07 16:45 "Re: Questions on TIFF LZW compression", by Thomas Richter
On 06.06.2011 18:55, Bob Friesenhahn wrote: Thanks for your insight, Bob. > While I am not an expert at TIFF compression issues, I suspect that you > are correct that the predictor has little value (and may cause harm) at > depths other than 8 (and perhaps 16) bits since the compressor works on > an octet stream. Question rather is, does it predict octects, or pixel values modulo 2^N? I'm not so much concerned about the compression performance - as you say, there are clearly better codecs available - but rather about correctness. I really wonder how specs as sketchy as the TIFF specs got accepted. > The value of the predictor depends on the nature of the > image. When Adobe produced a preliminary application note about > Photoshop CS2's added support for 16 and 24 bit floats, they also > defined new types of predictors which work better for that sort of data. I understand. Is there a newer spec than rev.6 available? I don't see much of this in the specs I have. > TIFF is not PNG. PNG has a huge number of filter mechanisms, but TIFF is > more of a "working format" so it focuses less on achieving the absolute > smallest file size. The ability of TIFF to directly store 10 bit data is > already an accomplishment compared with other formats which would be > forced to promote to 16-bit and then use compression to make the result > smaller. Sure, that's all understood. As said, I don't really care about compression, but I'm trying to understand the specs. Greetings, Thomas