The changes are non-destructive, same as for raw, stored as xmp data embedded within the tif file (similarly for jpg). ACR gives no warning that it is overwriting the original file. The pixel data is unchanged. Of course only Adobe programs will display the changes.
The changes may be "cleared" by right-clicking on the thumbnail in Bridge, invoke Develop Settings and choose Clear Settings. The tif file remains forever altered in that a history is embedded within the file, but for all practical purposes the changes are erased.
Thanks for your explanation, Richard. I've been fiddling around with your explanation for a bit to see if I fully understand it, which I probably don't, but it is more than sufficient for now.
First off, you confirmed what I thought is that the change metadata that would be caught in an xmp sidecar if working with a true raw image is instead embedded in the JPEG or TIF image that you changed in ACR.
Per your explanation, I see that apparently the only or perhaps the normal route to eliminate the changes and get back to the original images is to right-click on the image in Bridge (I have but don't yet use Lightroom), choose 'Develop' and 'Clear Settings' - that clears the last set of changes you made in ACR but does not 'eliminate' them - i.e., if you then right-click on the image in Bridge, choose 'Develop' and 'Previous Settings' you go back to the most recent set of changes you made in ACR.
Where it gets more confusing is that if I Open Object that ACR image in PS and then save it as a .TIF file, you can no longer get that right-click / 'Develop' option in Bridge - appears that the ACR changes are 'baked in' at that point. However, oddly enough, if I save that TIF image as a JPEG image, I can still get the right-click / 'Develop' option in Bridge on the JPEG but not the TIF version.
Just understanding things a bit better at this point was my objective and I appreciate your feedback on this issue - perhaps like a lot of PS or ACR stuff, somewhat complex depending on how deep you go.
Hope I didn't confuse anyone else with the above, but just wanted to provide some further rookie feedback on the issue. Your reply answered my question - thanks again for the assistance.
Yes and no. I drastically cut the exposure on a tif in camera raw, brought it into PS, and then saved it out of PS as a jpg. The changes were apparently baked in, i.e. when I opened it with a non-Adobe application the image was underexposed.
I then right-clicked in Bridge on the jpg, chose Previous Conversion, and the underexposure was compounded, i.e. it had been doubled and the image was almost black.
So I believe trying to find "truth" in other than what I initially described goes way beyond Adobe's intent (and probably testing) for the operations.
Fyi, before making and changes in either ACR or PS, I always save a tif copy of the image as "rev00" if it's an image that might have some value personal or otherwise. The idea being that I will never intentionally make any changes to a "rev00" image - when I'm ready to work with it I simply save it as "rev01" and work with that.
Notwithstanding the nature of ACR changes to raw or JPEG/TIF, I think I'll stick with my "rev00"/TIF philosophy as an ultimate go-back if I need it or want to try some different approaches to working with the original image.
Thanks again for your feedback,
Somewhat different issue, but I agree with you - keep the original pristine and safe, in at least two locations. I'll occasionally generate a tif via scanning, otherwise all of my original photo data is raw. In either event a copy is make locally and "in the cloud" before any mods.