If you need the final image to be in sRGB, it would probably be easier to use the ACR controls to map the colors into the sRGB space without clipping rather than initially rendering into ProPhoto and subsequently editing the image in Photoshop.
Bill, I was looking into DCRAW's source code but I feel a bit lost to answer this: DCRAW uses Camera -> XYZ matrices (provided to Coffin by Adobe), and then another transformation XYZ -> output colour space used. In fact both matrices are multiplied in advance to do Camera -> output colour space in just one step.
The question is: is it possible that the exposure level of a given pixel has an influence to determina whether it will fall inside or outside the output colour profile space
Think of a pixel in a scene captured with RGB levels=(10,22,45), if it was shot 1 f-stop more exposed, for sensor linearity it would be coded as (20,44,90).
Is it possible that (10,22,45) when converted to the output colour space falls into sRGB gamut, but (20,44,90) gets clipped in sRGB?
I want to believe then that if (20,44,90) clips in the output colour profile but (10,22,45) doesn't clip, is just for saturation (luminosity) reasons
, not because the Hue determined by the pixel of the scene can alternatively belong to or not belong to the output profile gamut. Right?
If the answer to all that is yes, it means the degree of exposure of the RAW data will affect the possibility of converting levels on a pixel to a given output colour profile, so the Exposure slider in ACR is a good tool, not only to cancel the effect of the white balance, but also to avoid clipping due to excesive input exposure.
Am I right?