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gedstar- I think he meant that when he exported the image from either ACR or LR into PS, he didn't notice that it was set for a low-medium rez version of the image, not the full rez version.
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Canonnn - I think that the answer to your question will probably be, "no", but it all depends on exactly what you did with the image after it was in PS. For example, you mentioned that you composited it. Sometimes, if the images are in good shape when they go into PS, all you have to do to make a composite is set up some masks, move the component images into the right places, and do some minor lighting adjustments with adjustment layers. If that is the case with this particular composite, then you can probably get away with simply up-rez'ing the old PS file by the appropriate factor, and then replacing the content with new higher rez versions. The reason one might be able to get away this is because the layer masks needed for many composites (and obviously, all adjustment layers, masked or not) can be up-rez'ed much more without problems than actual pixel content can be (fake) up-rez'ed.
OTOH, if you did substantial pixel-level work on the component files after they were moved into PS, then you probably won't be able to get away with just replacing the (fake) up-rez'ed low-Rez versions with the actual higher rez versions. Examples of operations that certainly won't carry over are the various forms of sharpening, cloning, etc. In addition, basically *any* destructive editing to the component images will have to be re-done, because these procedures are not "remembered" by PS.
Sorry, but I don't think the prospects are very good.
I hope I understood your situation.
Cheers,
Tom M