2000.12.18 06:08 "Re: Stripes in thumbnail", by Christian Bednarek

The published original G4 tiff file is in turn compressed in some format with the extension bz2, which is unknow to me, and for which I do not have the tools to decompress. So I can't even look at it.

Oh sorry, didn't think of that. I put the original back (~4.8MB).

scanlines in the original g4 tiff(s) cannot be correctly interpretted by LibTiff, and are simply (partially) skipped, leaving a (partially) blank line. Warning and error behaviour of the g3/g4 decompressors has been

Hm. Now as you mention it... there are warnings. But as I'm an absolute newbie, I didn't put them in relation to the stripes...

• code to get LibTiff to read the original grayscale files
• code to convert an image from grayscale to cmyk
• code to get LibTiff to write the cmyk image

You should be able to handle the first and third with the aid of the LibTiff docs. If you have any additional questions (preferably more specific, if you expect an answer), just ask 'em.

Yes, I think this should be possible for me, in case I get enough time to learn about TIFF :)

I can elaborate on one way to get you started on the second task. Photoshop can save .ast files, which contain a lut to convert between lab and cmyk. The Photoshop SDK docs contain more info about this. So, one way would be to convert grayscale (which is essentially RGB, with r=g=b) to Y (XYZ with X=0 and Z=0), Y to L (Lab with a=0 and b=0) and finally L to CMYK using an .ast file/lut.

wow... it's _that_ complicated? But I did forget to mention, that those thumbnails don't have to be accurate. It's enough for me - and the task it's needed for - to find that a part of the picture is green and not red. So red=255-cyan, green=255-magenta... is quite good enough.

Christian