Bandwidth Conservation Society / Tutorial
The GIF format is the common image denominator for web publishing. A versatile format, it allows for graphics to be compressed in a variety of ways. The big deal is the number of colors available. We'll show you how to make an 8 bit gif, 3 4 5 6 or 7 bits, but still achieve acceptable quality. Plus... comparisons of how an image looks at various bit depths.
Palettes Most GIF files you see on web today are made up of an 8-bit palette. Means that there are 256 available colors in any given picture or graphic. But, in most cases the palette can be reduced, which reduces the file size of the GIF, yet still retain acceptable image quality. (For instance a 6-bit GIF only uses 64 colors but can reduce the file size by over 25%)
And, the GIF format allows for the definition of an alternative color palette. Rather than using the standard 256 colors of your system palette, the GIF file can redefine the 256 colors in the palette. (Note: on some 8-bit video displays, with some browsers, this might get weird.)
The bottom line is that by reducing the palette (bit depth) you also reduce the file size. This chart shows the bit-depth vs number of colors:
(Note: For comparison purposes, we've included several formats in these examples. Depending on your bandwidth, you may experience a slight delay as these images load. There is no more than 50K per page.)
Compare this 8 bit GIF image (16,618 Bytes) using the adaptive palette option in Adobe Photoshop to:
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