quick question JPEGs edited in ACR

Hi all,

quick question: does editing JPEGs in adobe camera RAW affect the quality as you keep editing the file? Or does it preserve the file and keep memory of the edits in some sidecar file? My brain tells me no, but I want to confirm this, since I can't see any sidecar file. Thanks!

The critical point in working with JPEGs is when they're saved. Successive edits of the same file, in whatever processing software, without saving will not affect the quality. It's only when they're save that compression is applied, and it's the compression that reduces the overall quality. I've read that more recent versions of Photoshop are able to differentiate portions of JPEG files that are edited from those left unchanged by an edit, and that only the edited portions of files are subject to additional compression and therefore additional quality drops from earlier versions (I don't know whether this info. is actually correct, but that's the Internet for you).

thanks for the reply. So if I save over the original file, this will detiorate its quality. But if I (and I always do this) have ACR save the file somewhere else, then the original will stay intact and only the new copy i saved will have this compression/deteriorat​ion applied?

Sfordphoto wrote in post #7841124
thanks for the reply. So if I save over the original file, this will detiorate its quality. But if I (and I always do this) have ACR save the file somewhere else, then the original will stay intact and only the new copy i saved will have this compression/deteriorat​ion applied?

That's right. Never save an "in progress" intermediate copy as a jpeg -- it's best to save it as a tiff or PSD, then only use jpeg as your final output.

But as far as your original question, yes, ACR uses the "non-destructive" approach to applying adjustments -- you can click "Done" and the actual image is not changed but the editor changes will be in the library and the changes will show up in Bridge.

No deterioration occurs. The editing instructions generated by ACR are stored in the header fields of the JPEG, not with the image data. Because of that the quality of the image is never affected. It is also the reason that you can revert to the original simply by using the Develop Settings > Clear Settings command.

This is the same for all rendered file formats like JPEG, TIFF, PNG, etc. XMP sidecar files are only created for RAW formats.

Sfordphoto wrote in post #7840885
Hi all,

quick question: does editing JPEGs in adobe camera RAW affect the quality as you keep editing the file? Or does it preserve the file and keep memory of the edits in some sidecar file? My brain tells me no, but I want to confirm this, since I can't see any sidecar file. Thanks!

That only matters when using a pixel level editor like Photoshop or Photoshop Elements which requires the jpeg codec to decompress/compress the file. ACR is a metadata editor; the jpeg codec is never involved since the instructions are stored in the file header fields. So when editing in ACR it doesn't matter if you overwrite your file or save a copy; the original image data is never really changed. But it is still good practice to save a copy; your file integrity is maintained from the standpoint that the EXIF "Date Modified" field remains intact.

Sfordphoto wrote in post #7841124
thanks for the reply. So if I save over the original file, this will detiorate its quality. But if I (and I always do this) have ACR save the file somewhere else, then the original will stay intact and only the new copy i saved will have this compression/deteriorat​ion applied?

thanks for the replies guys. very helpful! consider the question answered!