I have both Lightroom (5.6) and Photoshop (CC 2014.1.0) both set to operate using ProPhoto RGB. Lightroom is set to use it for external editing in Photoshop CC 2014 (via a TIFF), and Photoshop has it set as the default RGB color space. When select a raw file that I'm working on in Lightroom and choose Edit in > Edit in Adobe Photoshop CC 2014, it opens in Photoshop CC 2014 as the a fore mentioned TIFF file in ProPhoto RGB color space. But I just noticed that the histograms shown by both applications differ significantly even though, as far as I can tell the images match. Here's the histogram from Lightroom:
And here's the histogram from Photoshop:
Do I have something set up wrong? I don't really understand why they differ. I'm seeing clipping in the blue channel in Photoshop that isn't there in Lightroom. I know Lightroom uses the Melissa RGB colorspace, but my understanding was that this was a linear version of ProPhoto RGB. Is the linear/log nature of the two color spaces the cause of the differing histograms? What am I looking at here? Any thoughts would be great. I can't see that this is negatively impacting my results, but I am certainly curious as to what is going on.