Metadata (EXIF, IPTC, DC) for PNG
PNG is my preferred format for archival storage of photographs. It is lossless and more compact than TIFF and TIFF-LZV.
While the creators of the PNG format anticipated that metadata should be embedded with images, by the provision of allowing a single file to consist of several "chunks", there is yet no standard for embedding metadata in PNG image files. Specifically, PNG does not support more or less establishes tagsets such as EXIF, IPTC or DC.
Today, I searched for developments in this area, as well as general image metadata resources. It look as if most of the work is done in the late 1990ies. Also, since those involved seems to be librarians(?), rather than photographers, there is little concern about preserving out-of-camera EXIF metadata. Below is pointers to what I found:
- Exif.org: An unofficial site promoting Exif
- Adobe: Extensible Metadata Platform: Adobe's metadata framework XMP
- IPTC.org: IPTC Metadata for XMP: Using IPTC within Adobes XMP framework
- Creative Commons: XMP Recommendations: Guidelines for XMP metatags in CC projects.
Papers and notes:
- W3C: Describing and retrieving photos using RDF and HTTP: Note on W3C framework for embedding metadata in images for retrival over HTTP.
- Jane Hunter & Zhimin Zhan: An Indexing and Querying System for Online Images Based on the PNG Format and Embedded Metadata: Research paper.
Software and Projects:
- Project to embed EXIF metadata in PNG files (appears to be abandoned around December 2000).
- JHead-XML: Adding XML output for jhead EXIF parser: Tool to extract well-formed XML from EXIF JPEG metatags.
- Phil Harvey: ExifTool (Perl): Great program for manipulating EXIF and IPTC metadata. Supports PNG, but Photoshop don't recognise its tags.
- David Beckett: Pngmeta - tool for extracting metadata from PNG-files.
- MWG: Metadata Working Group.
If you know about other photography metadata efforts, please leave a comment.