Pixels and Colors
Resolution isn't the only factor governing the quality of your images. Equally important is the number of colors in the images. When you view a natural scene, or a well done photographic color print, you are able to differentiate millions of colors. Digital images can approximate this color realism, but whether they do so on your system depends on its capabilities and its settings. How many colors there are in an image, or how many a system can display is referred to as color depth, pixel-depth, or bit depth. Almost all newer systems include a video card and a monitor that can display what's called 24- bit true color. It's sometimes called true color because these systems display 16 million colors, about the number the human eye can discern.
How do bits and colors relate to one another? It's simple arithmetic. To calculate how many different colors can be captured or displayed, simply raise the number 2 to the power of the number of bits used to record or display the image. For example, 8-bits gives you 256 colors because 28=256. Here's a table to show you some other possibilities.
Black & white line art
Gray scale images
Number of Colors
Black and white images require only 2-bits to indicate which pixels are white and which are black. Gray scale images need 8 bits to display 256 different shades of gray. Color images are displayed using 4 bits (16 colors), 8 bits (256 colors), 16 bits (65 thousand colors) called high color, and 24 bits (16 million colors) or true color. Some cameras and image formats use up to 48 bits per pixel. These extra bits are used to improve the color in the image as it is processed down to its 24-bit final form.
In addition to affecting image quality, color depth also has an impact on file sizes. The more bits assigned to each pixel, the larger an image file becomes.