You can often switch formats to save even more bytes. For example, you can often substitute PNG-8s used with or without dithering for JPEGs or GIFs at smaller file sizes. Figure 6-4 shows the effect that file format and quality have on file size.
|TIFF LZW Comp. = 84.4K||
BMP 24 bit = 73.3K
JPEG Max Qual. = 40.5K
GIF 6 bit - 90% dith = 10K
PNG 6 bit - 90% dith. = 8.7K
JPEG Med. Qual. = 6.3K
Figure 6-4. Image file size versus format
TIFFs, BMPs, and maximum-quality JPEGs are unsuitable for the Web (see the first row of Figure 6-4, all greater than 40 KB saved from original in Photoshop). Switching to a different format can make a significant difference in file size. The PNG in Figure 6-4 is 13% smaller than the GIF at equivalent settings.