P: Information on .acr files

[Robert Ripps]

In my current image download folder, I see a bunch of acr files, which still bear their original import file naming, along with my NEF files and their corresponding xmp files. Most are small- 9-26k, but some are quite large, several MB in size.

As I understand it, the acr files have something to do with masking, but what I want to know is when I renamed my NEF files, and the corresponding XMP files got renamed, should the acr files have gotten renamed as well? I do not see any acr files that have been renamed to match the NEF/xmp files.

If I still have those acr files in the folder, but they still have the original file import names, does that mean that when I deleted some raw files in Lightroom, it did not remove these acr files, and they are now safe to discard now?

Photoshop 25.11.0, Lightroom Classic 13.4, Camera Raw 16.4., macOS 14.6.1

[Robert Ripps]

I am still getting these “orphaned” acr files – looking at the unchanged original file names and trying to pair them up with my renamed images, it does seem like they are images that I had done some retouching in Adobe camera raw while in Bridge, but not sure why there’s separate acr files or why they were not renamed with my new file names. Most are small, although images where I’ve done more retouching are usually larger, but I have one that’s almost 40 MB in size, and all I did was retouch out a tiny edge of the building against the solid blue sky.

I am wondering if it is it safe to delete them? I have Lightroom set to save all changes into XMP files, and I’ve also manually saved everything in Lightroom.

[Rikk Flohr: Photography]

"what I want to know is when I renamed my NEF files, and the corresponding XMP files got renamed, should the acr files have gotten renamed as well? "

How did you rename these files? 

[Robert Ripps]

I always do a batch rename in Lightroom Classic, which also renames the xmp files at the same time. Thanks.

[Rikk Flohr: Photography]

So if I have it right: 

1. Edits raw file from Bridge to Camera Raw, .acr files are created.
2. Files are subsequently imported into LrC
3. Files are batch renamed in LrC?

[Robert Ripps]

My workflow is to download the card using Lightroom Classic, applying a development, preset, as well as adding my copyright metadata, then doing a basic edit to get rid of any obviously bad images. At this stage, Lightroom Classic has created the xmp files, based on my camera naming convention.

I then go to Bridge, do my exposure, color, balance, and any other corrections that need to be done as I find it faster and easier than doing this in LRC. I then go back to LRC, saving all the changes back into the database, then do a tighter edit, again deleting some images, adding numerical ratings, and usually my image specific metadata. I then do a batch rename of all the files, which rename the corresponding xmp files.

I usually do not look to see if any acr files are created, and usually discover them later if I happen to look in the folder I downloaded the images to. I’m guessing they are being created when I’m doing my retouching in ACR through Bridge, before renamed the files.

It seems like if I do any further retouching on an image using ACR, it is creating a new acr file, but using the renamed file convention. Looking in the computer, the oldest acr file I can find is from August 9, 2023.

[JohanElzenga]

.acr files are what Camera Raw uses to store AI masks. Lightroom Classic does not use them. It can read them on import (or when you use 'Read Netadata from Files'), but Lightroom Classic stores these masks in its catalog (in the catalog.lrcat-data file). And if you write metadata to files, then Lightroom Classic writes the AI mask data into the .xmp files (which can become huge as a result, because this is not very efficient). Because that means that .acr files are obsolete for Lightroom Classic, it does not rename them if you rename the images.

[Robert Ripps]

So it sounds like you’re saying once I’ve renamed the files and saved them in LRC, the acr data is going into the Lightroom database, but if I open the file directly from the Finder, Photoshop is able to find that same data in the corresponding xmp file, correct? So I could trash all the acr files at some point. Although strangely as I mentioned one old acr file is about 40 MB but the corresponding xmp file is only 181K, yet in the Photoshop ACR window, it is showing my retouching properly.

[drtonyb · Accepted solution]

@Robert Ripps 

If you Import a raw file into LrC and edit in Develop, the settings are stored in the catalog. Any AI Masking or Removes are stored in the catalog folder with the .lrcat-data appended. If you choose to save from LrC to the .xmp sidecar file, the settings and AI masking/removes are all saved to the .xmp file, making it potentially large.

If you then open the raw file in ACR, the .xmp file is read and settings applied to the photo. The AI masking/removes are written to a new file with the .acr extension and are removed from the .xmp file when Camera Raw is finished (Done or Open in Ps). The .xmp file is small again, but there is another sidecar file, the .acr file.

If you then return to LrC and Read Metadata from File, if the .acr file is available, LrC will read it into the catalog along with the other settings from the .xmp file. Now that LrC has all the metadata it needs to continue editing, the .acr file is no longer of any use to LrC. If you rename the file in LrC, the .xmp file gets renamed, but the .acr file does not. Whether this changes one day, who knows, but as far as editing the renamed file in LrC is concerned, the .acr file can be deleted.

ACR creates, writes to and reads from .acr files, which it uses to store AI generated data. If the .xmp file has this AI data saved to it by LrC, ACR will extract it from the .xmp file and save to a .acr file, making the .xmp file smaller.

LrC only reads .acr files when Read Metadata from File is done and once read, it is no longer needed by LrC. If the .acr file was deleted before being read by LrC, AI Masks and Removes would be flagged as needing Updating, which could generate entirely different content than previously generated. Not good.

From your workflow description, I understand: Import into LrC; apply Presets and some edits; save to .xmp; edit further in ACR; back to LrC and read metadata from .xmp (and .acr); and rename file (.acr is orphaned here). If you need to go back to ACR, you must save the settings again to .xmp. ACR will read that and create a new .acr file if needed. The orphaned .acr is no longer needed by LrC or ACR, so can be deleted.

I hope this helps.