The purpose of the Channel Mixer adjustment layer is to allow us to control
the mix of each color channel to determine the resulting colors and tones in the
image. Specifically, for a RGB image, it allows us to mix the various
amounts of Red, Green and Blue.
Figure 1. Channel Mixer Dialog Box
The basic way to use this method is to first look at the red, green and blue
channels individually on the Channels panel. Find the one that looks
closest to the desired results. Reactive all channels, switch back to the
Layers panel and create a Channel Mixer adjustment layer. When we first
open the Channel Mixer dialog box, it defaults to Red at 100%, Green and 0% and
Blue at 0% and the monochrome box is unchecked. Change the color channel
in the Output Channel drop down box to the channel that looked the best on the
Channels panel and then click the monochrome box. Then move the three
sliders to fine tune the image. Do not change each percentage to 100%.
The percentage is not how much of a channel's information is used, but it's
weight in the total mix of information. Since it is usually best that the
total mix of information add up to 100%, then it is usually best if the three
channels add up to 100%. It is valid for a channel to have a negative
Theoretically, if we use Channel Mixer to set one of the
three primary colors to 100% and leave the other two at 0% and check the
monochrome box, it should match the image we see on the corresponding
channel in the Channels panel. I have found this not to be true.
The images are very similar, but they are not exactly the same in
To make reds a darker tone, decrease the red percentage. To make greens
a darker tone, decrease the green percentage. And to make blues a darker
tone, decrease the blue percentage. If we increase the percentages
instead, the change in tone will be reversed.
As we move the sliders, Adobe Photoshop uses each channel's percentage to
determine the weight that channel's information is to be used when calculating
the resulting black and white tone.
Figure 2 shows the resulting tone using the customary Channel Mixer method.
Figure 2 is just one of many results that can be achieved with this method.
Figure 2 was created using the Channel Mixer values in Figure 1 above.
The advantage of this method is we have control over the tones as we change the
percentages. The disadvantage is the balancing act that needs to be
performed to keep the total near 100%.
Figure 2. Custom Channel Mixer
Figure 3. Channel Mixer to Preserve Measured Tone
The Channel Mixer method is one of the most popular
customary methods. You can learn how to use Channel Mixer in the Tone
Management System (TMS) to retain measured luminance on the
TMS Measured Luminance page.