Originally posted by tlwyse Are you implying that it's not necessary to save your image in 16bpc but to simply keep it 8bpc since Photoshop still processes it "as if" it's 16bit?
When you open an 8bpc file and do color transformations, Photoshop does all the calculations in 16bit right up until you save, at which point the colours are interpolated back to whatever is determined in your file format. The end result is kind of irrelevant, because you're still starting and ending with an 8bpc file. You haven't added any color information, you've just done the color transformations more precisely.
But if your target is the utmost color fidelity, then you still need to start with a 16bit image. ACR and Photoshop are not the same application. ACR passes the color data to Photoshop in either 8bit or 16bit, and that step is important to ensure that Photoshop gets the right initial color data. In any case, I'd rather work with 16bit files throughout the whole process. That actually DOES increase the number of colors available me, unlike AdobeRGB which just changes which colors are available.
It's all kind of irrelevant for this thread, because the camera doesn't let you choose 8bpc/16bpc. It only lets you pick sRGB or AdobeRGB in 8bpc. I don't remember for sure, but I don't think JPG even allows 16bpc.
The upcoming versions of Gimp will also work this way, with an internal color engine that works in 16bit at all times. It can even be enabled right now, experimentally.