IPTC Checksum and MWG Rules

[lindon]

I'm a little confused by how the IPTCDigest checking works according to the MWG guidelines. Sounds like the stored IPTCDigest checksum is supposed to be compared to a computed checksum of the IPTC-IMM block, and if they're the same then the IPTC and corresponding XMP data are in sync.

If that's right, I don't get why that comparison tells you anything about the XMP data. Is it that XMP-unaware programs are also unaware of the IPTC checksum? Or is it that the computed checksum should be based on the corresponding XMP data (adjusted for IPTC field limitations)? Thanks for any help, pretty new to image metadata just trying to understand the logic.
Regards,
lindon

[Phil Harvey]

Hi Lindon,

I would have to re-read the MWG guidelines to be sure, but I think you are correct that the connection between the IPTCDigest and the XMP is tenuous at best.  It does seem that the system relies on the premise that software which doesn't update the XMP should not update the IPTCDigest.

- Phil

[lindon]

Thanks for the sanity check Phil. Amazing program by the way - congratulations!
Regards,
lindon