In this series, Helen Bradley discusses some handy Photoshop tools that are often overlooked or misunderstood, either because they’re hidden away or because their uses aren’t immediately apparent. Yet these tools provide smart and useful ways to perform various tasks in Photoshop, so they’re worthy of adding to your Photoshop skill list.
In this eighth part of the series, we look at channels, a feature that not only provides information about your image but can also be used for photo editing. You can use channel data to convert an image to black and white, and you can even save a selection in a channel for reuse later on.
When you open a photograph in Photoshop, it will already contain a number of channels. You can view them in the Channels palette by choosing Window > Channels. An RGB image such as a photo will have four entries in the channel list: one red, one green, one blue, and a composite channel made up of all three channels. By default you work with the RGB composite channel.
When you click on a channel such as the Red channel in the Channels palette, the other channels will be rendered invisible and you will see a grayscale image that represents the red in the image. In an RGB image, the areas that are darkest in the grayscale channel are those in which there is little of that particular color. The areas that are lightest are those with the most color. To see this at work, open a photograph that includes some blue sky, look at the blue channel, and notice that the sky area shows as white or light gray (see Figure 1). The opposite is the case with a CMYK image; however, as you’ll typically work with RGB color images, we will focus on them.
Figure 1 In an RGB image, the grayscale channels show the lightest values where there is more of that particular color in the image. Here the blue sky area looks almost white in the Blue channel.