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October 2006
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2006.10.14 17:52 "Re: SamplesPerPixel is 0 when loading image", by Joris Van Damme
Marcel, Thank you for the error report. Marcel Wiesweg wrote: > for the application digiKam (www.digikam.org) we are using libtiff in > our image loader. A while ago we received a bug report from a user > that opening certain 16-bit TIFF images failed. The report was later > on confirmed by another user. > Strangely, on other systems (on most systems, including mine) the > test image loads without any problems. As we all know, that is the hardest type of problem to debug. It's not even guaranteed that the problem is in LibTiff, it may be totally unrelated, as in a double free or out of bound memory access or race condition anywhere in unrelated code in the same process. Do you have any idea what might be the difference between the machines where it worked, and the ones where it didn't? Did you spot any pattern? > We investigated that the problem is that after calling > TIFFGetFieldDefaulted(tif, TIFFTAG_SAMPLESPERPIXEL, > &samples_per_pixel); the value of samples_per_pixel is "0" on the > affected machines, "3" on all others. This has been tested with > different versions of libtiff. > > The full story can be found here: > http://bugs.kde.org/show_bug.cgi?id=125916 > > The test image is > http://amigos.amiga.hu/dudeeg/digikam_tiff/IMG_4224-01.tif > > The source of out TIFF loader can be found at > http://websvn.kde.org/trunk/extragear/graphics/digikam/libs/dimg/loaders/tiffloader.cpp?view=auto > > Have you any idea what to do about this? The image seems perfectly fine to me. So does the loader code, more or less. (Though I have some unrelated remarks, like a fourth channel in RGB images isn't always an alpha channel, nor the other way around, you'd have to check the ExtraSamples tag. Also, from the looks of it, I think you'll get into trouble with a 16 bits per channel RGB images with multiple extra samples.) What version of LibTiff did you test? Have different versions been tested on the machines that gave a samples_per_pixel value of 0 in particular? How urgent is your problem? Best regards, Joris Van Damme info@awaresystems.be http://www.awaresystems.be/ Download your free TIFF tag viewer for windows here: http://www.awaresystems.be/imaging/tiff/astifftagviewer.html