B&W Processing with darktable - module choice & ordering

Software darktable
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I’m trying to improve my B&W processing skills with darktable 3.2.1 and have a question for everyone here.

While there is more than one way to convert a color image to B&W in darktable, I decided to focus on two for my use: 1) Channel Mixer, and 2) Lut 3D. For the record, Lut 3D is my preference - I’ve found some B&W Luts that - in my opinion - produce some good looking images. However, if I’m not going to use a Lut, I’ll use Channel Mixer.

Here’s my issue: Back when I was shooting B&W on film, I would expose a frame of film with a (for example) yellow filter over the lens. This would result in an exposed negative which would print with a darkened sky making the clouds pop more.

Now with darktable I don’t need to attach a yellow filter to my lens, I should be able to get the same effect digitally. To do this I convert my image to B&W using one of the two modules I described above, and then (ideally) use the Color Zones module to darken blues and greens (mimicking what a yellow filter would do)… However when I tried doing just that with Color Zones it didn’t work right, Color Zones having almost no affect. I think that is because the Color Zones module occurs in the pixel pipe AFTER both Channel Mixer and Lut 3D, so by the time pixels get to the Color Zones module, the pixels in the pixel pipe are just shades of gray - so there would be no blue and green pixels for the Color Zones module to work on.

Yes, I could do the B&W conversion AND darken blues in greens in one step - albeit for the entire image - by using just the Channel Mixer. However sometimes I might want to change the tonality of just a portion of the image (i.e., in addition to changing the sky, I also want to change the B&W tone of a red flower to separate it from green foliage), and I am not sure if the Channel Mixer is the right tool for that level of work.

I think the right tool for playing with color levels is the Color Zones module - and please correct me if I’m wrong here. (Yes, Color Balance is potentially an alternative to Color Zones, but it also falls after Channel Mixer/Lut 3D in the pixel pipeline, so I would have the same issues with it as I do Color Zones)

I know I can change the order of modules in the pixel pipe for a particular image, and when I tried moving Color Zones BEFORE Channel Mixer/Lut 3D, that made Color Zones work the way I would want. However, I recall an earlier admonition in the 3.x release to the effect of “only change the order of modules in the pixel pipe if you really know what you’re doing” - and I’m pretty sure that my knowledge of darktable is not at the “really know” level.

Part of my question is how to ‘best’ change the order of modules in the pixel pipe. I could either move Color Zones up in the pixel pipe so it occurs BEFORE Channel Mixer/Lut 3D (I’d use one of the two modules not both), or move Channel Mixer/Lut 3D down in the pixel pipe so it occurs AFTER Color Zones. To complicate matters a bit, I suspect that there is a possibility that I might have multiple instances of Color Zones if I needed to tweak a number of colors…

Hope my explanation is clear - please don’t hesitate to ask for clarifications.

Thanks!

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I don’t think changing pipe order is such a big deal anymore in 3.2.1, I mean they even let you save your own pipe order presets. But if you want to edit colour, then it of course has to be done before turning the image black and white. I’ll often move Lut module around, as it yields different results in different places. Ditto channel mixer. As channel mixer clips values it is not really ideal placed in between exposure and filmic. So when using it to turn image black and white, I would place it after all other colour operations. (So, I would move either Lut or Channel Mixer, and leave color zones where it is).

I personally have created channel mixer filters (saved as presets), to mimic the behaviour of coloured lens filters. You can see them on page 2 of this document (columns on the right):
The Channel Mixer.pdf (68.9 KB)
If you input these in ‘grey’ destination, blend mode normal, you will get black and white. If you input them in ‘grey’ destination, blend mode lightness, you will get colour. (Don’t use the ‘lightness’ destination - the red channel is buggy).

Another way is to turn output saturation slider of color balance down to 0.

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As Tim said, don’t be afraid to change the order of the modules if it makes sense for your purposes. You see what happens.

Channel mixer and color zones are a good combination to create black and white photos. I will also recommend getting to know the drawn and parametric masks well to be able to handle objects and areas individually.

I will show an example of a possible way to do black and white conversion. In this example I will use the color look up table for color manipulation, as an alternative to the color zone, because it allows you to select colors according to their brightness.

This is what the initial photo looks like with corrected exposure:

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First I will use channel mixer to darken blue sky (target - grey, blend mode - HSV lightness). With HSV lightness, despite the gray destination, the photo still retains its colors. It only affects the brightness. You can see that the sky gets darker and the clouds appear much better:

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Now I use a new instance of the channel mixer to see how the black and white version looks like:

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The clouds are clearly visible, but the photo still looks a bit flat. The contrasts are missing, especially between the sky and the field. I will darken the sky even more with color look up table module.

Note that the color look up table is in before both instances of the channel mixer in the pixelpipe, so it is not affected by either module and I can choose the colors freely.

With color checker I select a color in the sky and with shift+left-click I replace the color on one of the patches. (changed patch has a white frame). Then with the slider lightness i darken this color:

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Now I want to increase the overall contrast. I do this with the color balance module, which is located in the pixelpipe above both channel mixer instances, i.e. after the black and white conversion:

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Next, I would like to highlight the softly illuminated field with the help of a new instance of color balance. For this I use a drawn mask:

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And after the denoising the photo looks like this:

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Before and after:

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17 Likes
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Thank you for your very helpful reply!

While I routinely use darktable’s masks - at least in a basic way - there is much I have to learn about using darktable. At some point I had read the description of blending using HSV Lightness and looked at the Color Look Up module but honestly never thought of a way they could be relevant to my B&W processing.

it is very clear that I was wrong!

Your examples open new avenues for manipulating images for me, and give me hints of additional darktable capabilities that I should experiment with.

Thank you!

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This is great. Can you please explain why you add the step of the first instance of channel mixer with the HSV Lightness blend? Why not go straight to the color lookup module and darken the sky and reduce the number of steps?

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@s7habo thank you for this detailed explanation and example! I too would like to improve my black and white processing skills so this gives me some new things to practice.

Does anyone else have additional recommended black and white workflows, especially ones that follows the recommended list of modules to use with filmic and a linear RGB workflow?

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There are several reasons for this:

With channel mixer you can in many cases get the results very fast without the need of additional instances because you only mix three color channels.

But in many cases it is not immediately clear if the photo is suitable for black and white conversion.

In this case, I used the first instance of the channel mixer for two different purposes; to see if the photo was suitable for black and white conversion and to see how the changes would affect the color version.

Sometimes the color version is simply improved, especially if the photo has strong color contrasts, which are further enhanced in this way. Then I can decide whether to keep the color version or convert the photo to black and white.

With the second instance I increased the contrast between the sky and the field even more and because I wanted to have a part of the sky even darker I used color look up table.

So this was a process and not necessarily the “shortest” way, as it is not always clear what the result might look like.

With an instance of channel mixer and color look up table this would be possible too, but I’m not sure if this would be faster because you had to play with a lot of patches which could be quite tricky.

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This is freakin’ awesome, I’ve never considered the use of these modules, used these ways. I typically use ColourZones to eliminate saturation and lower the luminosity of blue to darker. Sometimes, to magnify that, I’ll use Multiply blending and while that darkens the blue, it also makes the blue visible so I’ll use the Monochrome module. To increase contrast, I’ll reduce the dynamic range in the Filmic module (negative numbers).

Some of the LUTs I have (free from ON1) produce quite nice results but I consider these to be out-of-the-box presets and because I don’t (know how to) modify the LUTs, I don’t think of them as being part of my “creative process”, I prefer to use my own methods and skills to be creative (which sometimes fails but, I think of failures as weaknesses in my knowledge that I need to acquire).

I’m going to try this method, thanks for sharing.

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:+1: This is the best way to learn, boost your creativity and develop your own style!

The modular structure of darktable is the ideal playground for this. I wish people wouldn’t be so scared and dare to experiment with modules much more.

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Definitely. I’ve learned so much from the ‘you-stack-em’ toolchain of rawproc, where I could add, omit, and change around things to see what would happen.

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What is your go-to method for working on individual colours or narrow colour ranges? For example, if you wanted to work on the reds of an image and adjust the HSL for a more orangey look, which module would you use? I would immediately think of the color zones module, but to work on hue, saturation and lightness, you have to work in three tabs and set up nodes for each one - not perhaps the easiest way to do it. Color lookup table has a much easier interface in this regard, where you can select a colour (or create your own) and then adjust the HSL quickly. But this works in LAB and probably not recommended anymore for a scene-referred workflow…

I know from previous posts you’re a big fan of the channel mixer module, but not sure this would be suited to working on an individual colour or colour range. So do you have any tips or recommendations for how best to approach this?

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I have none. It depends on the photo. This is often just trial and error method.

If it works, it works. I don’t worry too much about it.

:point_down:

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LAB is not a no go in scene referred workflow - you just need to take care it’s limits. At least when you’re having a b/w result in mind, inaccurate colors aren’t really a problem …

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I’ve experimented a lot but still haven’t found what I would call an easy way to work on the HSL of a particular colour. I was just wondering if I’d missed a trick somewhere.
I feel like an RGB version of the color lookup table would be great. I’m not always happy with the results I currently get from it. And the color zones module is great for working on the Hue, Saturation or Lightness individually, but cumbersome for working on all three at the same time.

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Have you tried the parametric masks? There’s usually a way to select on colour (a/b, or R/G/B iirc)

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How about a one nice “Play Raw” where you can describe your difficulties and we can look at it to see with which approach we can find the solution?

The advantage of this is that it becomes concrete and many people can participate with the result that different ways of solving the problem can be found.

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For sure I’ll post a Play Raw if I come across a concrete example. But I’m not really having any difficulties per se, I can usually always get the results I’m looking for. I was just wondering if there were easier or cleverer ways of working with modules for individual colours. I brought the topic up because some of your posts (like this B&W one and the Channel Mixer one) bring up new techniques I’d never thought of before and I find them enlightening. Also, I realized there was no direct equivalent of Lightroom’s colour mixer module, which I remember from my Adobe days. It allows you to play with the HSL on individual colour ranges very quickly and easily. It’s nothing special, but it is very simple.

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Is there a reason that you and everyone are making this so complex? Maybe I am missing something? Why not use color zones to do your B&W conversion? Just select the black & white film preset in color zones and then adjust the colors to get the B&W look you want. That is what I do.

Note I am a complete novice darktable user. I am just trying to learn how to use it and experimenting right now. If all goes well then maybe I will leave Lightroom behind. I am using 3.2.1 on Win10.

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Image processing is complex, we just don’t try to hide that complexity.

If you’re happy with the look you’re getting, then keep going! Nothing wrong with that.

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Is my suggestion to the OP an inferior way to do what he wants?