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2010.06.11 21:36 "Class Y (YCbCr) tiffs with 420 subsampling", by Thomas Richter
Hi folks, It looks libTIFF has a bug in handling YCbCr subsampled images, specifically with 420 subsampling. I have here an image of 64x64 pixels, 8 bits per component, and thus a total of 64*64+2*32*32 = 6144 bytes + overhead. Yet, libtiff complains that the "StripByteCount" is bogus. Here is more information on this file: out.tif: Magic: 0x4949 <little-endian> Version: 0x2a Directory 0: offset 8 (0x8) next 0 (0) ImageWidth (256) LONG (4) 1<64> ImageLength (257) LONG (4) 1<64> BitsPerSample (258) SHORT (3) 3<8 8 8> Compression (259) SHORT (3) 1<1> Photometric (262) SHORT (3) 1<6> StripOffsets (273) LONG (4) 1<158> SamplesPerPixel (277) SHORT (3) 1<3> RowsPerStrip (278) LONG (4) 1<64> StripByteCounts (279) LONG (4) 1<6144> SampleFormat (339) SHORT (3) 3<1 1 1> YCbCrSubsampling (530) SHORT (3) 2<2 2> 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. The image is attached. Greetings, Thomas