|TIFF and LibTiff Mailing List Archive|
LibTiff Mailing List
1999.10.29 03:27 "Re: Stupid TIFF question: tags in ascending order", by Daniel Mccoy
I know of no language that explicitly states that any tag should appear only once in the file, but the fact that the spec does not specify what a reader should do in the case of duplicate tags is a strong indication that the authors intended it to be interpreted as strictly ascending order. If you want to write tiff files that other programs have a chance of reading, you are much better off taking a conservative interpretation of points like this. If you are thinking of writing files like this, it's a very bad idea. If your intention is to store extra information that way, just get a private tag, you can make it variable length if you want and store pretty much anything you want in it. >Hi. The TIFF 6.0 Specification says, >"The entries in an IFD must be sorted in ascending order by Tag." >Stupid question: does this mean strictly ascending order? >In other words, is it legal to have the same tag twice (or more) >in a single IFD? If so, how is a TIFF reader supposed to interpret >situations like this? Ignore the earlier tag? Ignore the later tag? >Something else?