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April 2005
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2005.05.02 18:48 "Re: Color TIFF/JPEG compression questions", by Bob Friesenhahn
On Mon, 2 May 2005, Joris wrote: > > > So, I think that tiffinfo might be playing correctly here (since it > > agrees with tiffdump, and I don't see any obvious problems with the > > code.) > > We should check that we are talking about the exact same quad-jpeg.tif. I know > for a fact that AsTiffTagViewer shows exactly what is there, and, unlike > LibTiff, that stuff isn't burdoned with an actual image decoder part and a > subsampling-fixup scheme and such... So if AsTiffTagViewer doesn't mention the > tag, and tiffinfo does, I know for a fact that tiffinfo must be wrong. Tiffinfo seems to dump information the way libtiff would handle it (e.g. includes some defaults). Tiffdump should be used to produce a raw dump of TIFF information. > A newer version of AsTiffTagViewer that isn't published yet, also supports hex > viewing of just about any structure in a TIFF file. With this version I was able > to triple-check, and sure enough, the tag count of this IFD shows as 14 in a hex > dump that is merely a hex dump and cannot possibly be wrong. 14 is the number of > tags shown by both versions of AsTiffTagViewer. So tiffinfo *does* add the > default or fixed-up or whatever values of YCbCrSubsampling even though the tag > is *not* there. I am still eagerly awaiting the release of this software. :-) Bob ====================================== Bob Friesenhahn bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/