I was poking around the NAPP website and found a great tutorial on using Adobe Camera Raw to independently edit different areas of an image by switching back and forth between ACR and PhotoShop. It was a video, so I wrote my own narrative based on some work I did. I did this in CS4 but I think it also works in CS3 and possibly CS2. But as with all thing, your mileage may vary (I don't know about the right-click in step 5 for earlier versions).
From what I’ve learned you can only do this with two separate layers/areas (I tried a third and it just wouldn’t work right). I was playing around with an old image that I took and loved being able to do all of the editing work – including cropping, straightening and sharpening the statuette, etc. – in ACR. All I used PhotoShop for was to create a new Smart Object layer, make a selection, and insert a mask. Then I separately edited that second layer in ACR independent of the first layer.
Here is a Before and After:
Here is how I did this:
1. Open the original RAW/DNG file in Adobe Camera Raw.
2. With an eye on the portion of the image you want to edit, make adjustments in ACR – Cropping, Expousre, Blacks, Clarity, Luminance/Saturation, etc. In my case I focused on the statuette.
3. Instead of just opening the image, hold down the shift key. This will change the “Open” button to “Open Object,” which you should click on.
4. The image will open in PhotoShop as a Smart Object. In the Image thumbnail you will see a little Smart Object icon in the lower right-hand corner.
5. With the background layer highlighted, select Layers, Smart Objects, New Smart Objects via Copy. Or you can right-click on the background layer and select New Smart Objects via Copy from the menu that opens.
6. A new Smart Object layer will open. Again, in the Image thumbnail you will see a little Smart Object icon in the lower right-hand corner.
7. In the new layer, using the selection tool (I used the Quick Selection tool) highlight the areas of the image that you were ignoring while previously editing in ACR. For my image, I highlighted the statuette, clicked on Select, Invert, so that all the surrounding area was selected.
8. Double click on the new layer and it will open in ACR.
9. Edit to get the surrounding area looking the way you want it. I my case I wanted to deepen the blue background.
10. Click on Open, which will return you to PhotoShop.
11. Things may look all out of whack at this point. With the second layer selected, click on the “Mask” icon at the bottom of the layers panel (the icon is a little camera).
12. Now you’ll see the image from the background layer sort of pop over the second layer (it doesn't really, but you get the idea).
13. From this point onward, you can double click on each layer to return to ACR and manipulate them as you like.
One note of warning, if you are going to crop do it in your first session of ACR or at least before you create the second layer in PhotoShop. Things will get a little strange if you do the cropping in ACR later.
You will notice that through out this tutorial I did not create any other layers to manipulate the image. I only toggled into and out of ACR from each of the two Smart Object layers to make my edits. I could have gone through each and every step I took in ACR but it was all specific to my image. What I did learn is that this works really well when there are two very distinct areas to work on. When the difference are difficult to separate it becomes a bit more challenging.
While the statuette may not look very much changed from the original photo, it did go through quite a lot in ACR. And the background was really changed very radically. I had a few more images to include in this tutorial for some of the steps with this tutorial (really just an image on the selection) but you can see them on my Flickr page.
What you see is a color image that I manipulated. I have used the same image and made the background completely black (that includes the wood stool you see as the modeling table). So there is a lot you can do with the procedure. And in another image I brought up the stool a bit while keeping the background black. There is a lot of playing you can do with the technique -- and it's all non-destructive because you are working with a RAW file.
Even though what I did was a very simple image, this is a very powerful tool if used properly. I find myself using it more and more. I'd rather do as much editing in ACR as I can because it doesn't degrade images.