Anatomy of an Image

A digital image is, of course, composed of a grid of colored pixels. The color of an individual pixel in an image is usually specified using three numbers, one for the red information, one for the blue, and one for the green. If your final image is an 8-bit image, then 8-bit numbers are used to represent the pixels in each channel. This means that any pixel in any individual channel can have a value between 0 and 255. When three 8-bit channels are combined, you have a composite 24-bit image that is capable of displaying any of approximately 16 million colors. While this is a far greater number of colors than the eye can perceive, bear in mind that a lot of these colors are essentially redundant. RGB values of 1,0,0 (1 red, 0 green, 0 blue) and 1,1,0 are not significantly different. Therefore, the number of significant colors in that 16 million-color assortment is actually much smaller.

If your image is a 16-bit image, then 16-bit numbers are used for each channel, resulting in an image that can have roughly 35 trillion unique colors. Though the difference between 1,0,0 and 1,1,0, will be the same as in an 8-bit image, because each pixel of each channel can have a value between 0 and 32,768, 16-bit images have more significant colorsthat is, more colors that your eye is capable of seeing.

It's important to understand channels because some edits and corrections can be achieved only by manipulating the individual color channels of an image. What's more, some problems are easier to identify and solve if you are in the habit of thinking in terms of individual channels. Finally, as you'll see later, an understanding of color channels makes it easier to make better use of your image editor's adjustment and correction tools.