"Black & White conversion" tool: How in the world does this work?

FlowtographyBerlin

Ok, I hope someone knows this, because a lot of you are using Lightroom:

I'm preparing to switch from Aperture to Capture One. For B&W conversion, CO doesn't have a channel mixer anymore, but only this B&W conversion tool thing that's also used in Photoshop ("Black & White" panel) and in Lightroom.

Now, this thing mixes up the world of subtractive (YMC) and additive (RGB) logic, six sliders. I get that each one of these sliders touches the "sensitivity" for the respective color. But that doesn't help me, because I need to understand the logic that's behind this thing. A channel mixer is very intuitive, because it simply mixes the three "channels" of the negative, just like you could back in the analog world (well, theoretically, but that's another discussion).

If it was YMC, I'd be ok with that, too, because it's simply the complementary of RGB, and the logic of filtering the negative to the positive. Doesn't matter.

With this "new" tool, though, what the heck does it actually do? So let's say, a "zero all sliders" setting corresponds to a certain mix of the channels, in case of CO, it's 30% red, 60% green, 10% blue. Now, when you move the "yellow" slider (not included in the logic of RGB), what happens? When you move the "green" slider, what happens?

And most of all: How do you achieve a 100% red-, green- or blue-channel conversion with this thing?

Does anyone happen to know of a documentation of this strange algorithm that somehow explains what's going on? As Photoshop and Lightroom are using it as well, chances may not be so bad, but I couldn't find anything until now. (I'm not talking about those "How-to-get-nice-black-and-white-pictures" tutorials that just tell you how to move some sliders.) I really need to understand this thing as I want to be able to make B&W conversion like I did before.

Thanks very much for any help on this, folks!

FlowtographyBerlin

P.S.: I already asked in the Phase One forum, and no one so far knew. I also emailed PhaseOne support, and neither could they explain it. Just so you know :-)

Ironheart

I think you may be overthinking it. The sliders simply map to those tones, so you can dial them up and down. They are not channels at all.

FlowtographyBerlin

@Ironheart: Thanks for your answer.

However, I don't think that trying to understand a tool so I can use it properly is "overthinking it". It's the only tool available for B&W conversion in Capture One (and LR, I believe), so I'd like to be able to use it.

Just like knowing what different blend modes in Photoshop do (overlay, hard light, soft light etc.), will enable you to use them for the purpose you want.

Or omagine using RGB gradation curves or the levels tool without knowing what it does, just by fiddling around with it until it "somehow fits".

No one here who knows this?

Ironheart

I've played with the tool, and I'm telling you it's just a tone map. It has nothing to do with color channels. That's all I meant by over thinking it. The red slider controls all of the "reds" and the cyan slider controls all of the "cyans". Thats it.

FlowtographyBerlin

@Ironheart, thanks for your answer. I'm not saying it's a channel mixer, I'm asking how to achieve the result that you get with a channel mixer, as the ones above are classic conversions.

So what you're saying is that this thing has a basic conversion setting (e.g. R30% G60% B10%, as in CO, don't know about LR) that you can then modify?