The channel mixer is basically 3 modules in 1: - using the red, green and blue destinations, it allows you to effectively do a matrix multiplication on the [R,G,B] vectors: [Rout] [Rr Rg Rb] [Rin] [Gout] = [Gr Gg Gb] x [Gin] [Bout] [Br Bg Bb] [Bin]
You use the sliders on the red, green & blue destination tabs to input the 9 coefficients of the matrix. Transformations between (linear) colour spaces are usually achieved by matrix multiplications, and you can use such a linear transform to "tweak the primary colours" of your colourspace (basically transform to a different colour space with slightly different primary colours). This is a fairly technical thing, and if you try to find suitable coefficients by "trial and error" I think it may be quite difficult to use unless you keep the adjustments very small, or use it with a mask. The following article has an example where this feature of channel mixer was used together with a mask to adjust the blue light from LEDs to bring them back into gamut. https://discuss.pixls.us/t/darktable-3-0-for-dummies-hardcore-edition/15864 - converting the image to monochrome. Basically, for each pixel it is setting the R,G,B values to the same value (which is a well-behaved colourspace results in some shade of grey). There are different strategies for how you decide which [x,x,x] value to map an [R,G,B] vector to (eg. averaging, max, etc.). Here I think there is nothing wrong with just using the presets to find a suitable look. - using [R,G,B] values to influence Hue, Saturation & Lightness (HSL). I'm hard pressed to understand what you would use this for in practice, and I saw a discussion on github which seemed to indicate the implementation here may even be broken. On Wed, 2 Sep 2020 at 05:05, Mikael Ståldal <[email protected]> wrote: > I have tried to use the channel mixer module, but I don't quite > understand it. I have only been able to effectively use the presets. > > I have read the user manual, but it didn't help much. > > I also looked at this video: https://www.youtube.com/watch?v=ZGvkSTjjtMw > but it seems like Bruce Williams was quite confused as well. > > Any suggestions for documentation or tutorials? > > ____________________________________________________________________________ > darktable user mailing list > to unsubscribe send a mail to > [email protected] > > ____________________________________________________________________________ darktable user mailing list to unsubscribe send a mail to [email protected]
