Ordered Dither for Netscape Greys

The following text is a copy of part of the text appearing on my main palette page. You may have noticed that the 6x6x6 color palette has very few greys. In fact, if you don't unclude black and white, there are only 4 greys. This is a severe limitation of this palette. In many cases, you can achieve a reasonable result by using an ordered dither. The following is an image containing not only the greys of the 6x6x6 palette, but the intermediate greys.

Here is a magnified version of how the image looks on a 256 color system:

If you are on a 256 color system, you will see some dithering in the intermediate colors. The dithering rendered by Netscape is a pseudo-random dither. In some cases, an ordered dither will look much better. Here is the same image rendered with an ordered dither instead.

I chose a dither which is essentially a checkerboard pattern. This seems to produce the best results if an even color is desired. Netscape does not dither this second image because it has already been dithered to the Netscape colors. This is an example of choosing the dither for optimal effect.

One caveat, however: using an ordered dither in a GIF image will increase the file size. The difference is minor in this example because the images are small. However, this can become a significant consideration on larger images.

Go back to Victor Engel's No Dither Netscape Colors Go back to Victor Engel's Home Page

http://www.onr.com/user/lights/greymag.html

This Page Copyright © 1996 Victor S. Engel
This page and any of its contents may be reproduced only under specific conditions. Addendum to my general copyright: the image contained in the file netcol.gif may be freely copied in any form desired by anybody as long as the colors are not altered, the URL remains on the image, and the copyright notice remains. In other words, you may port the image to other formats, but do not change the colors or alter the content.