2005.12.22 19:52 "Re: [Tiff] Custom Tags, Private Ifds and other questions", by Chris Cox

The other option is to register a single tag, and put multiple values in there.

Photoshop takes this approach - with one private tag containing it's own style of IFD like directory (the same as used in the PSD file format).

If you are going to use new tags, you must register them (actually, obtain new tag numbers) with Adobe to prevent conflicts.

Chris

On 12/22/05 11:09 AM, "David Scriven" <davidwriter@yahoo.com> wrote:

We are intending to release a program under GPL that will use TIFF files. The program requires that 13 or more custom tags be set.

Looking at the TIFF 6.0 manual it indicates that if you have 10 or more private tags you should create a private Ifd, but looking through the archives, I sense that there are some who dislike the whole idea of a private Ifd. I would like some guidance on the following questions:

1. Should one use a private Ifd?
2. If the answer is 'yes' how does one create a private Ifd. Andrey mentions some tricks with libtiff - is there a code snippet that someone could share?
3. I've been using a modification of Andrey's pgm (2003.11.17 - "Fetching custom tags") to set and fetch the custom tags (Thank you, Andrey) - how would one modify this for the private Ifd tag?
4. Since these files will definitely be out in the wild, what should be registered, and with whom?
5. I'm using version 3.6.1 under Fedora Core 3