Channels can be used to remove some color casts. For example, an image with a blue cast can be adjusted by selecting the Blue channel as the channel to work with in the Channels palette, but ensure that the RGB composite channel is visible so you can see what you’re doing. Choose Image > Adjustments > Levels and drag the Levels Midtone slider to the right to remove the blue cast (remember that the darker areas of a channel represent less of that color).
Finally, you can give an image a surreal look by altering its colors using the Channel Mixer. One method is to add a new Channel Mixer adjustment layer and set the Red Output Channel to 100% Green. Set the Green Output Channel to 100% blue and the Blue Output Channel to 100% red. This alters the colors in the image, but retains the details—often giving you startling results (see Figure 8).
Figure 8 By using the Channel mixer you can replace one color in the image with another to create more artistic effects.
As you can see, channels have a myriad of uses, ranging from the practical to the artistic, and they’re a must-know tool for creating great black-and-white images.