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 single color channel (R, G, or B) can be viewed as a grayscale image, where the lighter the image, the lighter the corresponding color will be.
- You can include values from another channel to modify your current channel values.
It’s a common enough adjustment method that it shows up in many different editing programs. Here is the same control in GIMP, RawTherapee, and darktable:
So, let’s look at an image. Here’s the lovely Sarah Carag from a couple of years ago:
If you set the Green and Blue channel respective green/blue sliders to zero (0), you’ll see just the red channel representation of your image:
It’s probably easiest to focus on a single channel for the moment, but this applies to all of the channels in the mixer.
These are the values of red in your entire image. If you were to now adjust the green slider in the Red channel, you would see that you weren’t really introducing any green color into the image, but would actually be increasing the total amount of red. For example, I’m going to raise the green slider to 50 in the Red channel:
This now adds the Green channel values to the Red channel (50), increasing the total red channel values.
You can see how the red channel blows out now on her cheek and forehead (the values have reached their upper limit and are clipping).
To see what this does to your normal image, set the Green and Blue channel sliders back to their default (Green channel, green slider = 100, Blue channel, blue slider = 100):
Here’s the original image again for comparison:
Notice that you haven’t introduced any green colors into the image by adding it in the mixer, but rather have adjusted the Red channel values instead.
Make a note, this is important:
Adjusting color sliders in a channel for other colors won’t change the color of the channel, just adjust that channels intensity. (in the Channel Mixer).
It’s simply another way to adjust the color intensity/value on a channel-by-channel basis, using other channels as a modifer. (You can also subtract from your channel by using negative numbers).
I don’t normally use the mixer for much outside of B&W conversion in my normal workflows, but one thing you can try when looking at images of people is to make minor adjustments to favor the red channel values overall, as it’s generally pretty on skin tones.
Try something subtle like bumping the Red channel reds a bit, dropping the Red channel blue/green to counter, and bumping red slider in the other channels, while dropping the corresponding sliders:
Here’s the original image again for comparison (again):
I would experiment, keeping in mind that modifications in a channel will ultimately only alter the values of the channel color (how they mix is a different story… and in fact is one of the ways to adjust WB for the image by pushing/pulling each channel to achieve a desired balance).