Is there a way to import additional color spaces into Camera Raw? If I have a file that is not in one of the standard color spaces, and open it in camera raw I believe i am viewing the file with my chosen default Camera Raw color space, not the color space of the file. Then if adjustments are made and the file is saved it will be saved in the chosen Camera Raw color space. The color space choices in Camera Raw are limited. Is there a way to import additional color spaces into camera Raw?

No.

Bummer!

Are you talking raw or jpeg/tiff?

If jpeg/tiff, as long as the file has an embedded profile, Camera Raw (and Lightroom) will use the embedded profile–but understand that if you have CR process the file, it will be transformed from the embedded profile into CR's internal processing space which is ProPhoto RGB colors and a linear gamma. You would NOT be able to use the embedded profile for this processing anyway (the odds that ANY other space would work is exceedingly small).

After processing, you could export (or save out) a regular ProPhoto RGB 16 bit file and to a convert to profile to get it back into some other color space...but why bother?

My goal is to soft proof my Camera Raw adjustments in the Camera Raw viewing window, using the final destination profile. Then save the file using that color space.

That's not possible at this time. You'll have to soft proof and convert in Photoshop. But then, it would be more prudent for most users to apply output specific tweaks (over a good working space like ProPhoto RGB) on layers since most people have multiple output needs.

I think so, but it is not so simple.

If you convert the native raw image in DNG format, the DNG converter adds color conversion information to the file, in form of several matrixes. This information relates to the conversion from the camera's color space in CIE XYZ, and from there the conversion depends on the target color space. ACR too uses that information when processing the raw data.

Going backwards, one could find alternative conversion values, which, when applied to raw data of that particular camera would lead to a different color space, although ACR would still believe, that it arived at ProPhoto.

Changing the DNG file is a piece of cake. However, calculating the required conversion matrixes may not be so simple, particularly, because the DNG file contains two sets, for two different illuminations; the conversion values for other illuminations will be derived (interpolated) from these given sets.

Note, that the conversion values are constant for any given camera model.

I am not sure if I would go this way, except perhaps if this kind of raw processing were a major part of my occupational activity.

I work on, and archive all my master files in the ProPhoto RBG color space.
I just wish that after I made a copy of the file and converted the file to the destination space, I could use Camera Raw for the image specific tweaks for that color space.