Pixel Graphics

Unlike many design applications, the computer graphics used on WWW pages is not vector-oriented, put pixel-oriented (see [2], chapter 1). This implies that a graphical design on a computer screen is represented as a rastered area of small, colored dots of the same size. Or you can view the image as rows made up of color dots placed next to each other. An image of 640 by 480 dots (or pixels) would have 640 dots per row, and 480 rows (which is the standard screen resolution of a Macintosh computer).

For the designer, this has several consequences for producing on-line graphics:

1. Images have a fixed size - if you try to change their size, they usually lose quality. You need to design them in their final size from the very beginning.
2. Not all computer displays have the same color representation (or even number of colors available for display). Most computers support 256 colors nowadays, although some older PC's still might be stuck with 64 or even 16 colors. A design with few colors will look appropriate on such machines, but a photographic logo or very colorful images will be dithered and will look very coarse.
3. On computers without 24-bit graphics (sometimes this is called true-color display or 16.7 million color mode or millions of colors) the operating system might reserve some of their colors for windows, buttons and other parts of their user interface, and a computer with 256 colors on-screen might end up with 224 free colors for image presentation. This will result in your 256 color design being dithered, a process that usually doesn't make it more beautiful.