@Morgan_Hardwood @heckflosse Thanks for the swift reply guys!
So I did some more experimenting last night and here’s what I found.
- Yes you were right about the A and B channels of LAB. If they are used then the image will not be fully BW no matter what else you do and how many of the many saturation sliders you pull down to 0.
- RGB saturation does act differently, but I do remember knowing about that from back in the day. Before the BW conversion tool I used to use the LAB Saturation slider.
- Even with the A and B channels untouched, I’d get a slightly different value, usually in the blue (1% or so more than the others) when I’d monitor a spot, and I concluded that it’s due to CIE environment which was on. I did however not want to go without it because I liked the contrast it produced.
- I tried to dial down all the saturation sliders I could find, and it finally worked when I turned down the Saturation and the Chroma sliders in CIE - though note, that even though the exported JPG will have equal amounts of RGB in each pixel, the RawTherapee spot measuring tool still gives slightly different measurements between the channels for any given pixel. Weird.
I wonder if a final “desaturate” checkbox could be implemented at the very end of the chain in order to just be sure and not need to measure pixels 