This took a surprisingly long time to figure out how to do, so I’m posting the answer here in the hopes that it’ll be easier to find in the almighty Google than the vague mentions on other pages that were tough to find.
I have a bunch of JPEG files that I wanted to open with the Adobe Camera Raw interface in Photoshop CS3. I knew that there was the option to do that from Adobe Bridge, and as far as I could tell from Adobe’s documentation, that was the only way. Unfortunately, both Photoshop and Bridge CS3 use so much memory just to have them running — even if they don’t have any images open — that I didn’t want to deal with slowing down my Photoshop editing with extra swapping caused by having Bridge open as well. And I have a bunch of JPEGs to work on, so I wouldn’t want to open and close Bridge all the time to keep memory usage down.
As it turns out, there are two options to open JPG files in Camera Raw without having to use Bridge at all.
The first is to go to File > Open As… in Photoshop, and from the pull-down menu where you choose what to open the file as, choose “Camera Raw.” This will open whatever file you select in the ACR interface, and works just fine for JPEGs.
The second option is to go to Edit > Preferences > File Handling. Under the File Compatibility section, there’s an option labeled “Prefer Adobe Camera Raw for JPEG Files.” If you check that, then Photoshop will run JPEGs through ACR by default. You can open the JPGs by dragging them to Photoshop, by using the standard File > Open dialog box, or any other way of getting Photoshop to open the file, and it’ll use ACR.
Hope that helps somebody. This is in Photoshop CS3, I have no idea if the same options exist in Photoshop CS4, since I haven’t used it yet. I’d expect it to have similar options, though. If anyone with CS4 can confirm that and post the answer here, that would be awesome.