XMP metadata lost from PNG files after saveing

[Hitz_M]

Hello,

i am using Photosop CS3 SDK. through my plug-in I put some metadata in the file using XMP SDK 4.4.2.

For PNG files, if the file is modified and saved, all the XMP metadata is lost from the file.

The following steps are being done.

1. Put some metadata in PNG file using SXMPMeta::SetProperty and SXMPMeta::AppendArrayItem

2. modify the file (changed brightness, contrast, flattened the image).

3. Save this file.

After saving all the xmp metadata is lost from the PNG file. This works for all other formats.

What can be wrong that I am doing?

Is there any other way to put XMP metadata in file?

Thanks,

Hitesh

[Chris Cox]

That's probably because PNG doesn't save or read XMP metadata.

There really aren't standards for metadata in PNG. (though a few products have tried adding it in ad-hoc ways, without documenting their efforts)

[Ardfry]

Doesn't Bridge do this?

Isn't this documented in the XMP spec (XMP in PNG)?

[Chris Cox]

It's not exactly documented.

There were a couple of incompatible drafts, and now we have different apps storing data in different places.

We've asked for clarification (and some cleanup), but haven't gotten anywhere yet.

[Ardfry]

> It's not exactly documented.

It's in the 2005 XMP spec as using the iTXt chunk, and I don't believe that was a draft.