The SO/ raw wasn't changed, some metadata about it might be. The equivalent of the sidecare, embedded I suspect in the PS document. If you had a raw and some metadata that said you wanted PV 2012, then you took both back to ACR or LR that was older than that PV, it wouldn't show it of course, it would "refert" to PV2010 or PV2003. I don't think that's different in Photoshop expect one would suspect the version of ACR understands the most modern features. But going back, it's the instructions that are not recognized. I don't see how the SO is different but again, I'm an novice in their use.
Hi Andrew,
Absolutely ... the embedded raw image isn't touched at all ... same as in Lightroom. There's no history in ACR and you can't go back into the SO and do an undo of a previous step, but the edits are totally reversible, so clearly the raw data isn't changed. The editing instructions must be stored as they are in a sidecar, but inside the psd or tif.
So there's no concern about losing the raw image (anyway, I always keep the original raw file with its xmp file, so I can always go back to that). That isn't my concern.
If you think of the Photoshop workflow it will make the issue clearer. OK, I open the image as a raw SO in Photoshop. Fine, no problem, I can then add adjustment layers, apply a sharpening filter to the SO, crop, straighten, whatever. Now I decide that the yellow saturation needs a tweak, so I double-click on the SO, do the edit in ACR and exit back into Photoshop. And so on.
Now imagine that this scenario happened not now, but in 3 years time, when Lightroom/ACR has moved on to PV2016, say, so that my SO has all of its adjustments in the PV2016 context (the sliders may be different to PV2012, the effect of the sliders may be different, the demosaicing algorithm may have changed, affecting the look of the image etc.). But now I decide I've had enough of CC, I don't want to continue to pay what has become an unacceptable annual fee for Photoshop, I am only using Photoshop occasionally by then ... whatever, basically I want to go back to the version of Photoshop I own, which is CS6.
I open the image in CC ... fine, no problem. I decide to make a tweak to the raw SO ... I go into it ... and, hey, everything's changed ... the colors have changed, the brightness has changed ... it's just wrong! When I go back into Photoshop the whole image has changed, even though I made no changes myself to the SO. The problem is that ACR has reverted to PV2012, but the raw image was 'edited' in PV2016. To give you an idea of how drastic this is, if you open a SO in PS CS4 that has been created using PV2012, the image is flipped horizontally, so left becomes right and right becomes left!
All is not lost, of course. I can go back to the original raw image and re-develop it; I can go into ACR and correct the image based on PV2012 editing, trying to get it back to what it was in PV2016. So it's not as though I've lost the original, I've just lost the ability to modify the raw SO without having to redo the whole raw phase of the development. It would be sort of equivalent to an image created in CC2016 with multiple layers, filters etc., opening fine in CS6, but flattened so that all the adjustment layers, smart filters etc are lost. Not quite as bad as that, but not far off.
Does that make sense? So then to ensure backward compatibility we should not move to the next raw process version, but stay in PV2012 as that will (should) allow us to go back to PS CS6.
The same thing is true of Lightroom ... if you go back to Lightroom 1 and try to edit a file that has been developed in Lightroom 5 with PV2012 you will have to pretty well redo the development. I think with Lightroom you can to some extent avoid this problem by using DNGs? But the problem doesn't really arise with LR at this point because we can (still) purchase it outright, so you can always freeze your development environment (that's assuming that what you freeze will still run on whatever OS is available in the future ... another whole can of worms!).
Robert