Today’s Question: Suppose that I deleted some xmp/acr sidecar files. Is there a way to regenerated or recreate them? Just hypothetically, of course.
Tim’s Quick Answer: If you’re using Lightroom Classic deleting sidecar files wouldn’t be a problem because the information is in the catalog. If you’re using Camera Raw you would lose your adjustments.
More Detail: Lightroom Classic and Camera Raw (and other software) use sidecar files to store metadata updates, primarily as a way of saving metadata to the source file without altering the proprietary raw capture. For example, with non-raw file formats most metadata that would otherwise be saved to a sidecar file would instead be written directly into the source image file.
In the context of Lightroom Classic, the sidecar files can be thought of as a backup to the information in the Lightroom Classic catalog. In fact, sidecar files aren’t created by default in Lightroom Classic. But if you do save the metadata to the source files, either using the Metadata > Save Metadata to Files command or by enabling the automatic option in Catalog Settings, those sidecar files contain information that is also stored in the catalog.
So, with Lightroom Classic if you had deleted the sidecar files for an image you could simply use the Metadata > Save Metadata to Files command to recreate the sidecar files.
With Adobe Camera Raw the situation is different, because the sidecar files are the only place that metadata is saved. Deleting the XMP sidecar file would cause general metadata such as star ratings and keywords, along with adjustment settings from Camera Raw, to be lost. Deleting the ACR sidecar file would cause pixel metadata such as masks from targeted adjustments to be lost. So if you’re using Camera Raw, in general you want to protect the sidecar files almost as much as you protect the original photos.
