Export SVG-metadata when exporting to PNG

[nojhan]

There is no clear standard for embedding metadata in PNG, but it would be nice to have at least a minor support of Exif.

Other softwares are working on it, for ex. : http://www.digikam.org/?q=node/62

[Tom Davidson (tjd-mit)]

Sounds good--any more details you can provide on a mapping from Inkscape metadata fields to, e.g. exif would probably help the chances of this getting implemented by one of the devs...

[nojhan (nojhan-gmail)]

The PNG specification (version 1.2) indicates :
« The iTXt, tEXt, and zTXt chunks are used for conveying textual information associated with the image. This specification refers to them generically as "text chunks".
Each of the text chunks contains as its first field a keyword that indicates the type of information represented by the text string. The following keywords are predefined and should be used where appropriate:
   Title Short (one line) title or caption for image
   Author Name of image's creator
   Description Description of image (possibly long)
   Copyright Copyright notice
   Creation Time Time of original image creation
   Software Software used to create the image
   Disclaimer Legal disclaimer
   Warning Warning of nature of content
   Source Device used to create the image
   Comment Miscellaneous comment; conversion from GIF comment »

Regarding inkscape, iTXt may be the good one to use.

More informations on the specs concerning chunks:
http://libpng.nigilist.ru/pub/png/spec/1.2/PNG-Chunks.html#C.Anc-text

[Alexandre Prokoudine (alexandre-prokoudine)]

While Exif support is nice, I'd rather suggest addressing XMP support instead

[nojhan (nojhan-gmail)]

One can want Exif, XMP, IPTC or DC, RDF etc. The problem I see here is that none of them are standard in PNG. Thus, one cannot be sure that all softwares can read (and more important, save after edits) the metadata.

A first simple step would be to use the iTXt chunk, with standards keywords. Then, as the specs permits to add new keywords, it should be possible to support XMP or a subpart of Exif as well (as far as I comprehend the specs, but I'm not an expert).

More infos:
* Some details on the keywords: http://libpng.nigilist.ru/pub/png/spec/1.2/PNG-Chunks.html#C.Anc-text
* Some links about PNG and metadata: http://heim.ifi.uio.no/~gisle/blog/?p=3

[Gustavo (ayala-gustavo)]

and the solution is...

[nojhan (nojhan-gmail)]

The standard iTXT chunk is the right solution.

I have made a python script to export a PNG whit metadata, using inkscape and PIL :
http://stripit.svn.sourceforge.net/viewvc/stripit/trunk/stripit.py?view=markup

One may want to look at it, use it as a tool for inkscape or whatever you think of...

[Jon A. Cruz (jon-joncruz)]

Metadata is now written for "Title", "Author", "Description", "Creation Time", "Source" and "Copyright". The copyright content might need adjustment.

Fixed in revision 19919.