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Web PaletteWeb Design in a Nutshell, eMatter EditionChapter 17Web PaletteCHAPTER 17
Designing Graphics with the Web Palette
When images with colors from the full 24-bit color space are displayed on 8-bit
monitors (capable of displaying only 256 colors), browsers do the best they can to
render the image using colors in their own built-in Web Palette. (Note that if the
browser is running on a 24-bit display, the Web Palette does not come into effect
and all colors will be displayed accurately.)
Remapping images to the Web Palette can result in unpredictable and undesirable
dithering. Not only that, sometimes flat colors shift to the nearest web-safe colors
without dithering. The algorithm for deciding which colors to shift and which to
dither (as well as choosingwhereto shift) differs depending on the browser brand
and version.
But because you knowexactlywhich colors will not dither, you can use the Web
Palette to your advantage by choosing these colors in the image creation process.
It requires a little extra effort, and an adjustment to a limited color choice, but the
payoff is that you get to see your image the way everyone else will, with fewer
surprises. It gives you, not the browser, control over whether and how the image
will dither.
If you don’t care about dithering or how your graphics appear on 8-bit monitors,
then this chapter is not for you.
The techniques in this chapter apply to graphics that use 8-bit palettes such as GIF
or PNG. Because PNG is not widely supported at this time, GIF is featured in the
following examples.
The Web Palette
The Web Palette consists of the 216 colors capable of being displayed by both
Macintosh and Windows systems. Therefore colors chosen from the Web Palette
will render accurately on Mac or PC displays (although they may still shift or dither
on low-end Unix displays).