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May 2005
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2005.05.20 18:30 "Re: TIFF/EP and TIFF 6.0", by Bob Young
Joris, Okay, thanks for the explaination. I may have been a bit inaccurate in my termnology, I'm looking at the TIFF/EP spec right now and it appears to rcommend the thumbnail be in IFD0 and the main image be a SubIFD. Here is the exact quote from the spec: Therefore, if the full-resolution image is stored using compression, the TIFF/EP file should include a thumbnail image stored in the 0th IFD that is readable by a baseline TIFF 6.0 reader. This thumbnail should not be compressed , and should be stored in strips, rather than in tiles, in order to be fully compatible with TIFF 6.0. A SubIFDs tag in the 0th IFD is used to point to the compressed full-resolution image. If the full-resolution image is stored uncompressed as a baseline-readable TIFF image, the full-resolution image could be stored in the 0th IFD. However, TIFF/EP recommends that a thumbnail image be stored in the 0th IFD, regardless of whether the full-resolution image is baseline TIFF readable or not. This provides a version of the image that is small (relative to the full-resolution image) and that may be quickly accessed by reader software. The use of the SubIFDs tag is the TIFF recommended method of performing this "treeing" mechanism.TIFF/EP requires that the SubIFDs "treeing" mechanism be used, rather than the "chaining" mechanism, to associate multiple resolution versions of the same image. So....why did Photoshop open the thumbnail, if IFD0 was clearly marked as the reduced resolution image and there was a SubIFD comtaining the main image, and the file was clearly a TIFF/EP file contaning a TIFF/EPStandardID tag? Does Photoshop not support TIFF/EP? In regards to my second question, I believe the above quote indicates that I can't use a YcbCr thumb if it is placed in IFD0 per TIFF/EP, as YcbCr is not readable by a baseline TIFF 6.0 reader