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2005.12.13 20:47 "Re: Writing EXIF data?", by Andrey Kiselev
On Tue, Dec 13, 2005 at 12:04:36PM -0800, Paul J. Lucas wrote: > > > No it doesnt since all the offsets inside the EXIF IFD are > > > relative to its start. > > > > For the sake of other mailing list subscribers and archive users: the > > above quote is incorrect information. > > No it isn't. Here's proof. Take the JPEG image at: > ... > Therefore, all EXIF metadata offsets for tag values larger than > 4 bytes are *relative* to the start of the EXIF metadata. Paul, That may have a sense for JPEG, but not for TIFF. Read the EXIF specification: "Value Offset This tag records the offset from the start of the TIFF header to the position where the value itself is recorded. In cases where the value fits in 4 bytes, the value itself is recorded. If the value is smaller than 4 bytes, the value is stored in the 4-byte area starting from the left, i.e., from the lower end of the byte offset area. For example, in big endian format, if the type is SHORT and the value is 1, it is recorded as 00010000.H." Note, that it is absolutely clean on the subject of the start position for offsets. And that explains why it works differently for JPEG: take a look where TIFF header starts in your file (offset 0x000c). Good for JPEG, but in TIFFs things become more complicated. Regards, Andrey -- Andrey V. Kiselev ICQ# 26871517