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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:

Portals:

Papers and notes:

Software and Projects:

If you know about other photography metadata efforts, please leave a comment.

13 responses:

Metadata for the PNG format

More that should interest every digital photographer: how to futureproof the storage of your images (and your metadata): Metadata (EXIF, IPTC, DC) for the PNG format. (FYI most digital cameras today store EXIF information with the RAW or JPEG images…

Trackback: Anders Jacobsen's sideblog.

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PngMeta

Readers may be interested in pngmeta – a little program which extracts metadata from png images and can give output in verious formats. Hope it's useful to you.

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Photoshop and png

This could be the reason I can't get Photoshop's metatagging for png's to work properly, then? (it seems to work, until you retrieve the saved file, then all the data (bar (C) status) is lost!

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Do you use Photoshop?

For working with an image, you could convert to PSD. Suppose you did archive in PNG w/ EXIF tags. What advantage would this have over PSD? Is it mainly the size that you are concerned about?

Would you ever need to edit the file again?

XMP might provide a way to get this in a standard format.

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Tools

I've been interested in the subject of meta data in graphics for a long time also.

With Photoshop's negligence of this functionality, I set for an extensive search quest for a tool that can embed XMP in PNG and found exactly what you found; in addition to one great free tool, PixVue, which is great in general except that it doesn't support PNG either.

I currently use the somewhat lengthy process of converting PNG to PPM and back again, and embedding the XMP in the PPM → PNG; using pngtopnm and pnmtopng tools from the netpbm toolset.

Some links that may help
  • TweakPNG: Utility for examining and modifying PNG files (windows) - download.
  • NetPbm: Tools for manipulating images (windows) - download.
  • Greg Roelofs: PNG – The Definitive Guide, O'Reilly - html-version. For example, look into chapter 11: PNG Options and Extensions.
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@David Blake
For me, I'd choose PNG over PSD mainly because PNG is not a proprietary format. This gives me more confidence that my archived photos will viewable in the future – not that I think Adobe will go under anytime soon, but an open format like PNG lends itself to being adopted widely by many different software suites and platforms (whereas including PSD into a photo viewing program involves licensing, etc.). Think MP3 vs. WMA. :)

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PNG for long-time storage?

Hi,
I would be interested to know if PNG still can be suggested as a format for long-time storage, especially in the light of the problems writing embedded metadata from certain current sw packages. I am currently writing a master thesis on sustainable methods and tools for maintaining and publishing digital imagery and would really like to include thoughts on this in my thesis.

Best regards,
Kjell Are Refsvik
Faculty of Computer Sciences
Østfold University College
Norway

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PNG is fine

@Kjell Are Refsvik,
PNG is fine for long-term archiving as long as it holds all the data you need: it's an open, royalty-free specification, so it can be supported in the future regardless of what companies are around.

If you need extra data, consider storing it in PNG comments (so that it is always with the file) and perhaps also in XML files, or in some other open format suitable for long-term use.

For many projects a more pressing question is at what resolution to store images, because of the cost and difficulty involved. If the images originate digitally, the original format should (also) be stored. if there is a non-digital source, then generally one wants the highest resolution possible. One might not normally (for example) want to archive a collection of scanned manuscript pages in GIF format with only 256 distinct colours…

Hope this helps both you and other readers… :-)

Liam

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XMP?

What about the latest XMP specification that defines tags for embedding EXIF within XMP?

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iTag

I found a program called iTag, that will tag PNG's. It uses XML (Adobe XMP Toolkit), not IPTC. I have used it for a while, and it seems to work fine (but I'm not an expert). And it's free.

Find it here: www.itagsoftware.com.

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@Keith - 2007-07-30 09:36
You can view .psd files in IrfanView. IrfanView treats .psd files like image files.

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Yes you can save Metadata in PNG using Photoshop CS5 & CS6 (even batch process it all)

I created an action for batch processing of my .jpg to .png in Photoshop CS5. It uses "save for web & devices" with PNG-24 and Metadata:All. CS6 apparently is more .png friendly. See these posts: http://forums.adobe.com/message/4413643 http://forums.adobe.com/thread/516779.

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