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  Web palette
    Often you will see graphics rendered with less colors than the original image has. The consequences can be quite disastrous for photographs. They will get spotty, have strange discoloration at the edges of areas with the same color, fine lines will be lost.
    Graphics with fading or gradated colors may suffer something similar. These will suddenly change in shade. 'Height lines' like on a map, will appear where one shade changes to another. New lines and color areas appear, changing the original image.
    These effects may be limited to some extent by dithering. This technique us used for areas with colors that cannot be displayed by the screen. The area is constructed with a mixture of two colors that can be displayed. Sometimes an ordered (chessboard) pattern, sometimes at random. This depending on software and computer settings.

palette palette
Windows palette 256 colors Macintosh palette 256 colors

    Until now I only spoke of VGA screens. Macintosh screens present a slightly different story. The standard Macintosh palette looks a lot like the IBM compatibles. But it is different as you can see above. But it gets worse. Some screens can only display one palette at a time. If you have two graphics with two different palettes, you will see only one with the right colors.

palette Web palette 216 colors

    To prevent problems, all graphics should use the same palette. A palette that can be used by Macintosh and IBM compatible systems. You can use a so called web palette to do this. This contains only the colors that are present in both system palettes. Graphics based on this palette can be displayed without problems by all systems. At least, if you have a screen that is able to display 256 colors.

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