When “non-destructive” edits start making changes to the original files…
A few days back, I was extolling the virtues of the Sidecar (.XMP) file format that Adobe uses for storing updated metadata and edits to digital images in Adobe Camera Raw (ACR):
“It turns out that Bridge (together with ACR) is exactly what I needed to organise my images, open them in ACR (and optionally Photoshop) to perform non-destructive edits, with the changes (and associated metadata) stored in Sidecar (.XMP) files alongside the original image (avoiding the need to maintain multiple copies of images.”
Well, soon afterwards I found out that, for raw image files, ACR does indeed create XMP files (which are also used by Adobe Photoshop Lightroom and are visible in Bridge) but, if ACR is used for JPEGs (or TIFFs), then the original files are modified.
Continues @ http://www.markwilson.co.uk
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August 26, 2008 at 7:53 pm
I’m fairly certain the ACR edits on JPEGs and TIFFs are still non-destructive, though they *do* modify the file. More clearly -
- Non-destructive – this means the edits don’t modify the image data itself, though there are metadata changes
- Yet the changes must be saved somewhere, and I believe the decision to inject them into XMP packets in the TIFF or JPEG is the correct handling, rather than generating sidecars (which is really only intended for files which cannot store XMP)
It may be possible to force the use of sidecars by setting the files in question to read-only.
Finally, you can test this yourself – open a TIFF in ACR, make a radical change, and click Done.
- First test that the edit was non-destructive is that the save process is nearly instance – if this is a large file, saving modified image data would not be instant.
- Second test – open the modified file in an image viewer besides an Adobe product – you should see the image as it was before the ACR edits, as those (non-Adobe) tools don’t read the ACR edits in the embedded XMP, and just display the image data as is.
Hope this helps,
R