darktable channels

A few questions and ideas regarding channels in darktable.

  1. Is there a way to view each R,G,B channel individually in gresycale, for the currently displayed image? I know they can be seen in colour when hovering the mouse over parametric masks input or output and hitting ‘c’, but it changes back to normal view as soon as you click away. Be nice if there was a little button, perhaps under the image by the toggle softproofing icons, to view each channel individually. If it already exists, can someone point me where.

  2. Is there a way to blend modules in each channel individually? Eg. I boost ‘exposure’ to +3ev, then slide input or output parametric mask in both R and G channels to 0, with the intention the adjustment will only affect the B channel. But I turn the exposure module on and off and nothing is happening, so it appears to have been taken out of all three channels, not just the two I turned down. Tried in Filmic module and same thing happened. Some may say the answer is to instead use blend mode ‘blue channel’, but if we wish to only boost exposure in the luminosity of blue channel we can’t do it, because we need the ‘lightness’ blend mode for that.

  3. In the channel mixer can we get the sum of each three sliders per channel, so we know when they = 100%?
    Two other ideas:
    a) A checkbox linking R,G,B to 100%. So if the box is checked, I’m in R channel and drag R down to 60%, G and B automatically rise to 20% each. Or if I drag G up to to 60%, R and B automatically lower by 30% each.
    b) Checkboxes to link two sliders proportionally. Eg. R/G, R/B, G/B. So if R/G is checked and I increase R by 20%, G will decrease by 20%, or vice versa, whilst leaving B alone.

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Just want to revisit this topic in light of the latest version.

Two ways come to mind, although not exactly what you’re looking for:

  1. In preferences > darkroom, you can turn change “display of individual color channels” to greyscale instead of false colour. Then when you press “c” while hovering over the masking controls, you’ll see a greyscale rendition of each of R, G and B.

  2. In the “gray” tab of color calibration, you can push up any of the sliders to 1.000 to see only that channel in greyscale. Save it as a preset, then do the same for the other two channels. This gives you 3 presets, one for each channel. You can then use an instance of color calibration as a “viewing” module for these individual colour channels. I’m not sure if this is a true representation of the channel however, especially as it will depend on the position of the module in the pixelpipe.

For modules working in RGB color space, there are RGB red channel/green channel/blue channel blend modes now, is this what you are looking for?

Thanks, yeah I started using the channel mixer/color calibration method, moving it to the top of the stack.

Not exactly. I was already aware of it. See point 2 in original post.