Learn how to use the Channel Mixer Adjustment to make creative color adjustments to your images.
Many people avoid using this adjustment mainly because they don’t understand how it works but the fact is you can create very nice color changes to your images if you get to know how to use it. In this tutorial I will try to explain how the Channel Mixer Works works and how to use it.
What is the Channel Mixer and How it works
This little adjustment, as its names indicates, works with the channels of an image. Most of the times we work on the RGB color space so the channels are Red, Green and Blue and you can see if you click the channels tab in the layer palette or from Window>Channels.
As you can see each channel is just a grayscale representation of the original color image but if you cycle through each channel you will notice that the same color has a different brightness.
For example you can see that the skin tones of the model are a lot brighter on the Red channel than on the Blue channel. The reason for that is because the skin tones have lots of red tones on them which makes them “shine” more on the Red channel. On the Blue channel the skin is darker because there there is only a little amount of blue necessary to get the colors of the skin.
The channel mixer works by mixing these grayscales, it doesn’t work with the actual colors of the image but with these channels and their grayscale mixing their brightness value.
For each Output Channel you have 3 sliders with the colors Red, Green and Blue and it works like this: Let’s take Blue as the Output Channel, if you select it you will see that the Blue slider is at 100% and the Red and Green are to 0%. This indicates that the Blue grayscale is at it’s default state which means that the amount of blues have not been modified.
If we now change any of these three sliders we will add or remove blue and yellow and that’s because we set the Output Channel to Blue and the opposite of blue is yellow on the RGB color space. So if you move the sliders to positive values you will add more Blue and if you sent them on negative you remove blue and add yellow.
We can recover the blue tones on the image with the other two sliders. All we need to do in order for the image to look right, is ensure that the Total amount located under the three slider is to 100% which is the total sum of the three sliders.
We can add 50% to the Red or 50% to the Greens or 25% to both. Let’s try with 50% for the reds and to what happens.
The reason why the skin tones got this magenta tint is because we added positive values (more blues because we are still on the blue output channel) to the reds which is the predominant tone on the skin. As you can see the vegetation are not heavily affected by the fact that we added 50% on the reds. Let’s see what happens if we add 50% on the Greens now.
Because we added 50% blue on the greens, they now look a bit darker and have a blue tint on it. The rest of the colors on the image were also affected but far less than the greens. Notice that the Total is to 100%. Basically this adjustment works like the Color Balance but but in a more complex manner.
You will also see a slider named Constant, which lets you control the let’s call it “offset” on the overall image: positive values add Blue and negative values add Yellow.
That’s how the Channel Mixer adjustment works in Photoshop. We only worked on the Blue Output channel but the other two work on the same principle, the only difference is the colors you add or subtract when you move the sliders. The image below illustrates it.