New Channel Mixer thread... how do you channel mix?

I have noticed that you don’t have base curve and also no filmic but have channel mixture, can you please explain, so the first instance of local contrast is with blend mode multiply? And second normal?

Exactly. The base curve processes the photo too much. It is used to imitate approximately the look of the JPEG file produced by the camera. I prefer to keep control over contrast and brightness myself.

The dynamic range of the photo is narrow enough. There is no need to use Filmic to compress it.

Here you can see some examples why:

Yes. I don’t think the order is important. Just try it yourself to see if there is a difference.

I am a subscriber of your channel and have seen it before but here also I have questions regarding using channel mixture with blend mode in some and not in others. Would appreciate if you can explain your edits with it in more detail, are you tweaking the R,G,B channels visually for a look? as CM is a mysterious module! till date I thought it is useful for B&W conversation only.

That is the basis.

If you select Target to Gray in the Channel Mixer, you can then use sliders of the respective color channel to mimic analog color filters used in black and white photography.

Here is an example of red filter:

Blue in the image (sky) becomes darker, red becomes brighter.

Here is an example of blue filter:

Blue (sky) becomes lighter, green becomes darker.

Green filter:

Green is getting brighter.

If I now only want to influence only the brightness of the image without losing colors, I use lightness blend mode and the result is for example like this (red filter):

Here is the original for comparison:

You can also influence the color mood of the image by selecting one of the color channels as target and much more:

This is a very powerful tool and is not specific to darktable. Every better photo application has it, and if you want to know more, check out the countless tutorials and information on the internet.

Channel mixer is part of the basics of photo processing itself.

6 Likes

In some of your examples you use filmic and in some you don’t depending on the dynamic range of the photo…… Interesting, I thought that you always needed to apply some sort of curve (base curve, filmic or a manually adjusted tone curve) to lift the luminosity of the midtones in the rawfile and to introduce some sort of s-curve, pronounced or subtle…… But that is not the case.

Yes and no. If you do not need to compress dynamic range, you can use Filmic to get a “filmic” look (compression of shadows and highlights) - typical for dynamic range distribution of analog film. And that is definitely better than base curve.

What bothers me is that this causes loss of local contrasts in these areas and I have to correct this later.

Yours answer seems to indicate that the channel mixer is an elementary and simple tool, easy to master. But that turns out not to be the case. Normally I enjoy the down-to-earth-how-to-use videos from Bruce Williams. I just watched episode 46 of understanding Darktable “The channel mixer”. Bruce Williams spends 21 minutes showing the audience that the channel mixer is somewhat of a mystery (if not used to convert photos to BW).

It’s a smart trick to use the channel mixer with destination grey and blend mode lightness to darken/lighten specific colors.

I have been looking for tutorials explaining how to use the channel mixer in an easy controllable way to fine tune photos but without success. Do you know some good tutorials?

I didn’t say that. I said that the channel mixer belongs to the basics of digital photo-editing, i.e. understanding the color composition of three primary colors; red, green, blue.

Colour filters in black and white photography were already used in analogue photography. One of the most important functions of the channel mixer is the imitation of these filters in the digital world. Channel mixer has also been around in GIMP, Photoshop and many other applications for quite some time.

What’s your goal? To fine tune what? Please give me an example, then we can talk more specifically.

Here is the explanation for channel mixer in the GIMP:

https://docs.gimp.org/2.6/en/plug-in-colors-channel-mixer.html

1 Like

Here is an excellent explanation of @patdavid how the channel mixer works:

3 Likes

I think @s7habo used that method in one of his recent youtube videos. I should watch that again too. I also find the channel mixer a bit abstract to understand. I found it helpful to try it on a color wheel.

Okay, let’s simplify things even more:

Besides the very nice from @st.raw here is one more:

I’m using GIMP channel mixer here because it’s easier to keep track. As you can see, as a starting point there are 3 active channels, red in red, green in green and blue in blue. On the picture you can see the composition of the colors. Sky is blue, grass is green and yellow:

Now watch what happens when I switch off the green channel (only red and blue remain - green in green =0).
Now we only have blue, red and combination between these two (magenta):

And now I add the green channel to the blue one (green in blue =1) And as you can see, the green grass is now blue too. So, we still have only two color channels (red and blue) but with the difference that I added the green channel to the blue and the green part of grass is now part of blue channel!:

So, in this simple example, I mixed two color channels together to achieve a certain effect.

Here is another example with red and green. We now have in the picture only red, green and the combination of both (yellow):

If I want the sky to be more “reddish”, I add blue to the red channel, because the sky is blue (for the most part) and the sky is now part of the red channel:

Now these were just two simple examples with only two channels to understand the logic. You can combine all three channels in countless ways by mixing three colours with each other. There is no mystery behind it, but, you have to take your time and experiment to find out how to combine the colors well. In painting, too, you have to learn this first.

4 Likes

I’ve learned a little of channel mixer using gimp too .

It was easier for me to start mimic other more familiar tools.

  1. exposure compensation
  2. white balance (using only red in red, green in green and blue in blue).
  3. Extract the red channel ( or green, or blue)
  4. desaturate using luminance formula
  5. add saturation https://www.imagemagick.org/discourse-server/viewtopic.php?t=9140
    http://www.trsqr.net/photokit/vs.html

A little homework for channel mixer to see if any of you have understood it :man_teacher::

In the last picture, the sky is orange:

Questions:

  1. Why isn’t it red?
  2. How do you get it red so that green grass stays green?

Here is the original picture:

Have fun! :wink:

Please explain it so that the others can understand it well!

@obe @s7habo Olaf this is a photoshop video but this young man is really good and the principle hold and I think he is offering the type of explanation you are looking for…totally applicable to DT https://www.google.com/search?q=editing+color+with+the+channel+mixer&oq=editing+color+with+the+channel+mixer&aqs=chrome..69i57j33.5623j0j7&sourceid=chrome&ie=UTF-8#kpvalbx=_qxeEXq_vIaHI1QGC5ZeQBg30

Thanks @priort , but I know how channel mixer works.

Problem is to explain it to people who don’t know how the color channels interact with each other. This means that it’s not always clear if it’s necessary to explain the color channels and the color composition itself before you get into explanation about channel mixing.

Just looping you in…I had now doubt you understood it…

Hi’ @priort @s7habo @age @st.raw

Thank you guys for your responses and examples. I really appreciate your input and I will study the material closer in the days to come….:grinning:!

I have read the “please help me to understand the “channel mixer” thread a long time ago, and I think this thread and your examples illustrate the (users) problem with this tool.
Channel mixer is complicated, because the red, blue and green channels interacts. I’m sure that you can make some adjustment, observe the changes and deduct why the changes took place looking at the color wheel.
But ideally, it should be the other way around. You observe a problem and decide to use the channel mixer as the appropriate tool to fix the problem and then do it.

The theme in many tutorials seems to be something like: if we add some red to the blue channel, what happens then? This is of course also the basic mechanism. The user manual section covering the channel mixer is rudimental. The destination can be a color channel or grey like in the tutorials but the destination can also be hue, saturation and lightness. What happens here and what’s the purpose of this?

Darktable consists of many wonderful tools (more than 70!), tools that are partly overlapping. If the white balance needs fixing then you use the white balance tool, of course. I suppose you, if you are “clever”, could fix the white balance using the channel mixer. But you would not do that, would you?
In which situations is the channel mixer be the ideal/natural tool to use?

noob’s answer (trying hard :nerd_face:):
1 - That sky contains blue, red and green
2 - When you reset the blue channel, it becomes green (see @s7habo’s previous post)

Forget the above for a moment.
If you have red and add blue, you get violet/magenta
If you add green to violet, you get orange.

So the green sky made of red+yellow became now violet+yellow, because red isn’t no longer red, since blue was added to it.
And violet + yellow gives orange.

This seem to be about primary and secondary colors, and I used as reference this color wheel.

1 Like

:point_down:

:flushed:

How can you fix something with the tool, that you don’t understand?
How do you know it’s good for anything if you don’t know what it does? :thinking:

:point_down:

I’m still waiting.

2 Likes

@obe This is one of the best visual demonstrations I have seen…https://www.youtube.com/watch?v=zgTLw31PVNs