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November 2000
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2000.11.14 00:58 "Re: Outstanding Libtiff Issues", by Tom Lane
Frank Warmerdam <warmerda@home.com> writes: > http://bugzilla.remotesensing.org/show_bug.cgi?id=23 > http://www.ai.sri.com/cgi-bin/digitalearth/list.pl?dir=sfbay.oi > The images at the URL above, in varying resolutions, are all tiled > YCbCr TIFFs with JPEG compression. Not all tools handle YCbCr TIFFs > or tiled TIFFs (or both), so it would be nice if tiffcp did. But > despite its lack of diagnostics, when run on such an image with only > the -s option, tiffcp produces a tiny file with mangled Y, Cb and Cr > components (at least judging by XV's output). For example, the > 512x640 level-4 image shrinks from 240k to 33k and changes from a > reasonable aerial shot (with black regions indicating no data) to a > mostly teal image. FWIW, I can't duplicate this problem using my current copy of libtiff (CVS sources from mid-April 2000, not too current I fear). The downloaded images look a little funny in XV --- are the strips supposed to be out of registration like that? --- but they look just about the same after being run through tiffcp -s. They do get a lot smaller, which is not too surprising given that the originals were saved at Q 100 :-( ... still another person who didn't read the libjpeg documentation I guess. > Since the tiles are (reported to be) 128x128 pixels, it should be > possible to losslessly convert such an image into strips of 512x128 > pixels (or so I would imagine--I'm no TIFF expert). Lossless reformatting of TIFF/JPEGs would be a major project; you'd essentially need to rewrite tiffcp from scratch to make it deal with DCT coefficient blocks instead of pixels. regards, tom lane organizer, Independent JPEG Group