TIFF and LibTiff Mail List Archive


1999.10.14 14:55 "TIFF Version validation", by Bill Comstock
1999.10.15 00:33 "Re: TIFF Version validation", by Tom Lane
1999.10.15 17:20 "Re: TIFF Version validation", by Thomas E Deweese
1999.10.16 05:04 "Re: TIFF Version validation", by Jaya krishnan Chathu
1999.10.16 22:00 "Re: TIFF Version validation", by Michael L. Welles

1999.10.15 00:33 "Re: TIFF Version validation", by Tom Lane

I'm interested in putting a large collection of TIFF images through a validation process, one that tests each image against a series of rules and reports whether it conforms to the TIFF standard and also which version of the TIFF standard it complies with. In other words, I'm looking for a utility that can report which TIFF version a particular TIFF file conforms to. If there is not such a utility, how would one know which version TIFF s/he is producing?

To my mind, even asking this question indicates a misunderstanding of the way TIFF works. There is no version number in TIFF files (unless you consider the famous "42" to be a version number, but actually it's just an identifying constant). Decoders are absolutely not supposed to decide whether they can handle a file on the basis of whether it is a "newer version" than what they know about; rather they are supposed to examine all the important tags and see whether they understand the contents of each one. For example, a decoder that encounters a Compression tag value that it doesn't support cannot decode the file. That doesn't necessarily mean that the decoder is an older version than the file is. The compression method could be one added by a more recent spec release, but it could also be one that the decoder author knew of and deliberately omitted support for, or it could be a private compression method of who-knows-what vintage. Conversely, a decoder could successfully decode a file that does use features not present in the TIFF spec version the author consulted, if those features are only in auxiliary tags.

A more useful way to look at things is a profile of features required to decode any particular TIFF --- for example, if your program said "tiled TIFF using LZW compression and containing 24-bit RGB data", that would convey helpful information. You can't usefully boil it down to "version 5.0" (or whichever spec release was the first one to mention all of those features), because almost no decoder supports the *whole* spec of any release.

regards, tom lane