How to work with Channel Mixer
To work with Channel Mixer
Select the Choose Colors tab from the Menu Bar and choose Adjust. After that click Channel Mixer.
Select a color channel to edit from the Output channel drop-down box. Your choices are Red, Green, and Blue.
If you want to create a grayscale image, select the Monochrome check box. This sets the Output channel to black. You can then move the Source channel sliders. They set the percentage of each channel used for the grayscale value of the final image.
The Source Channels are used to define the current channel you are editing. For example, if you select the Red channel in the Output channel drop-down box and then set the Red slider to 50, you reduce the amount of red in the image to 50% of its original amount.
The Constant slider brightens and darkens the image across all the channels. The default of 0 is the original setting.