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June 2010
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2010.06.12 16:18 "Re: Class Y (YCbCr) tiffs with 420 subsampling", by Thomas Richter
Hi Bob, >> I checked into the tiff directory reader (tif_dirread.c), which again >> calls TIFFScanlineSize(), which again only divides by the subsampling >> in X direction, but rather ignores the subsampling in Y direction - >> hence getting an invalid result. > > Please feel free to enter a bug via the Bugzilla bug tracker. Others > have complained about YCbCr strip size underestimation errors as well. > If you are able to produce a well-tested patch, and attach it to your > bug report, that will substantially hasten getting a fix into libtiff. > > Libtiff is essentially a community-supported project without a dedicated > maintainer so every bit of help is useful. Sure enough, however, I'm not quite clear on the semantics of TIFFScanlineSize(). Actually, if you do have subsampling, what is the the "size" of "a" scan line given that every other scanline holds only a subset of all samples? This is not at all clear. Given this problem, I'm not sure whether the bug is in TIFFScanlineSize() or in the directory reader. Any hints or suggestions? Once that is understood, it should be easy enough to fix... So long, Thomas