Photoshop Smart and Raw
Adobe added Smart Objects to Photoshop back in CS2 but many photographers didn't initially find much use for them. They were a huge help for graphic artists, but unless you often composited multiple images into a single document, they didn't provide much value over a more traditional workflow. All that changed with Photoshop CS3 and then changed even more with Photoshop CS4 and Camera Raw 5.
For many photographers, non-destructive editing is the holy grail of serious image editing. Any technique that allows one to refine choices they made in the past without loss today means they get better results without having to worry about image degradation. Many changes can be made on an adjustment layer, but not all, so when Adobe lets us do more non-destructively, it's worth taking notice.
Filters are one area that has long resisted non-destructive applications. Photoshop CS3 gave us Smart Filters which I've written about before. By encapsulating regular image layers as a Smart Object, you could apply many filters in a way that their settings remain fully editable. This even works with sharpening filters, which gave rise to my article about Smart Sharpening a Smart Object using a Smart Filter. Smart indeed.
But one Smart enhancement I haven't touched on previously is the fact that Camera Raw 5 and Photoshop CS4 let you easily open raw files as Smart Objects. For the photographer, this is really smart indeed.
Everyone knows that image optimization in Camera Raw is non-destructive, as it is in all raw converters. In the case of Camera Raw, your editing choices get saved in an associated XMP "sidecar" file rather than being applied directly to the raw image data itself. Other raw converters have their own methods of handling things, but all of them start from the premise that edits don't actually affect raw data. And when you think about just what a raw image is, this is quite understandable. With so much of what you see on screen when editing a raw image being the result of the specific interpolation algorithms being employed, there really is no straightforward way of making most edits directly even if you wanted to. Non-destructive editing is the name of the game with raw converters since that's really about all that is possible.
But while successive versions of Camera Raw let you do increasingly complex tasks while still working on a raw image, at some point you were forced to commit those changes and open the results in Photoshop if you needed to go beyond what Camera Raw was capable of. And the moment you did so, your non-destructive Camera Raw edits became cast in stone (well, cast in pixels, actually) and you had to live with them. Even if all your edits from that point forward were on adjustment layers or done via Smart Filters, the changes you made in Camera Raw were effectively baked in. Granted, you could always reopen your original raw file in Camera Raw. So long as you still had the associated XMP sidecar file you could resume your image tweaking non-destructively without any problems at all. But there was this boundary between your Camera Raw edits and your Photoshop edits that could not be crossed non-destructively. Go back to your Camera Raw edits and you'd lose your Photoshop changes. Stick with your Photoshop changes and you could no longer non-destructively tweak your Camera Raw optimizations.
Experienced Photoshop users may be aware that with a bit of work you could get around this barrier even back when CS2 was released by means of the File >> Place command on the Photoshop menu, but doing so always seemed rather cumbersome to me. Most graphic design programs have the concept of "placed" files as embedded references to other files. When you place a file in Photoshop CS2 or above, it creates a Smart Object. So to create a Smart Object from your raw image in CS2 or CS3, you had to first create a new Photoshop document the same size as the raw image you wanted to use. Then in your new blank document, you could use File >> Place and navigate to the desired raw file image. After selecting the image, you could click on the "Place" button to open it in Camera Raw. When you were ready, clicking on "OK" button allowed you to continue on to Photoshop where your raw image result would be placed in the center of your open document. After dragging the corners to fill the open image area and hitting the "Enter" key the Place command would be finished. At this point, you could delete your empty Background layer and continue as normal with editing your image. As I said, somewhat cumbersome, but it did work.
Camera Raw 5 lets you get around this obstacle in a much more elegant way. While it isn't obvious from the user interface, if you hold down the Shift key the regular "Open Image" button changes to an "Open Object" button. Rather than opening your raw conversion into Photoshop as a new Background layer, "Open Object" opens your image as a new Smart Object. Mission accomplished. Now if you need to tweak your raw conversion any you simply double-click on the Smart Object layer and it will reopen in Camera Raw just as it should. You'll be right back where you were with all your non-destructive changes still fully editable. When you're finished making changes, click on the "OK" button (again in the same place as "Open Image" generally is) and you'll be back in Photoshop with all your adjustment layers and Smart Filters still intact. In this way, you can take full advantage of Camera Raw targeted adjustments and other new tools seamlessly with the full palette of tools provided by Photoshop.
Regardless of which version of Photoshop you are using, it's a good idea to do as much as you can non-destructively. There's no telling if you might change your mind about a certain edit in the future, so why lock yourself in when you don't have to?