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December 2000
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2000.12.18 06:08 "Re: Stripes in thumbnail", by Christian Bednarek
On Mon, 18 Dec 2000, Joris Van Damme wrote: > 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