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

[s7habo (Boris Hajdukovic)]

@Rajkhand

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.

[obe (Olaf Berthelsen)]

@s7habo

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

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.

[s7habo (Boris Hajdukovic)]

@obe

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…

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.

[obe (Olaf Berthelsen)]

@s7habo

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.

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?

[s7habo (Boris Hajdukovic)]

@obe

Yours answer seems to indicate that the channel mixer is an elementary and simple tool, easy to master.

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.

@obe

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?

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

[s7habo (Boris Hajdukovic)]

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

Please help me to understand "Channel Mixer"

Ok, I’m assuming you’ve read the link I posted earlier. The channel mixer is most commonly found in tutorials around the idea of two main approaches: (Awesome|Amazing|Incredible|<insert-hyperbole-headline-here>) B&W creation using Channel Mixer! Color/White balance adjustments. Now, to be fair, the Channel Mixer does offer a lot of control when creating B&W images, but it also happens that it may be the easiest way to understand what’s actually happening. That is, basically, two things. A…

[st.raw]

@obe

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 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.

[s7habo (Boris Hajdukovic)]

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.

[age]

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

[s7habo (Boris Hajdukovic)]

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

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!

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

[priort (Todd Prior)]

@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 editing color with the channel mixer - Google Suche

[s7habo (Boris Hajdukovic)]

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.

[priort (Todd Prior)]

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

[obe (Olaf Berthelsen)]

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….!

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?

[gadolf (Gustavo Adolfo)]

@s7habo

Why isn’t it red?

noob’s answer (trying hard ):
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.

[s7habo (Boris Hajdukovic)]

@obe

Channel mixer is complicated, because the red, blue and green channels interacts.

@obe

You observe a problem and decide to use the channel mixer as the appropriate tool to fix the problem and then do it.

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?

@obe

You observe a problem

@s7habo

Please give me an example, then we can talk more specifically.

I’m still waiting.

[priort (Todd Prior)]

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

[s7habo (Boris Hajdukovic)]

Great! I hope now you have information that you need:

I look forward to the results.

[age]

This is how i see the channel mixer for artistic color grading

example:
cyan + magenta = blu

original

what if we add cyan and magenta to blu?

add cyan and magenta in blue, add yellow to green

saturation

cinematic , similar to (teal / orange)

[quote=“s7habo, post:69, topic:17025”]
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:
[/quote]

Here you have added yellow and red to blu, yellow + red= orange

[priort (Todd Prior)]

Thanks Boris hopefully the transition to the DT channel mixer was obvious but your pic makes the point…I just thought the gentleman that is a retired teacher…explained and demonstrated it very well for anyone following the thread…thanks for the exclamation point…