2011.06.07 16:45 "Re: [Tiff] 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