Adjusting Color Depth
Color depth is a way of describing how many colors your hardware and software are capable of displaying. The buzzwords most often used are 8-bit, 16-bit, and 24-bit. Of course, color depth is sometimes described by the actual number of colors being displayed, such as 256 colors or 16.7 million colors.
Hardware is the real determining factor. Your Web browser, for example, will display as many colors as your system can use. The next limiting factor is the type of image being displayed. GIFs are capable of displaying only 256 separate colors. However, these colors can be chosen from all 16.7 million available colors. JPGs can display up to 16.7 million colors, which makes the JPG format a popular choice for photographs and other real-world images.
Eight-bit or 256 colors is what some systems use, although they are often capable of displaying more. Sometimes referred to as Video Gate Array (VGA), 8-bit is somewhat limited. With your system set to 8-bit, you're at the mercy of your browser software, as you'll see later, in the section on palettes.
Sixteen-bit color, often referred to as "hi color," is a good choice if your system's video memory is limited. Using 16-bit color is a great compromise between speed and color. With 16-bit color, up to 64,000 colors are possible (65,536 actually). With 64,000 colors, your Webviewing experience will be much more enriched. Using this color depth reduces the need for dithering.
Dithering , a process used to fool the eye into seeing more colors than are actually available, is discussed in depth a little later in this chapter.
Twenty-four “bit is the best color depth to use when creating and viewing computer images. To use this color depth, though, your video card must have at least 1MB of memory. The reason is that for each pixel you must have 24 bits (or 3 bytes) of memory available. With a little simple arithmetic, you can see that a 640x480 screen, which has 307,200 pixels (640x480), requires 307,200x3 bytes per pixel, which equals 921,600 bytes. Now that you have a basic understanding of color depth, it's time to look at palettes.