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Figure 6-4. Image file size versus format

Chapter 6 - Web Page Optimization

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 balloon saved as bmp
BMP 24 bit = 73.3K
balloon saved as max jpeg
JPEG Max Qual. = 40.5K
balloon saved as 6 bit gif 90% dithered
GIF 6 bit - 90% dith = 10K
balloon saved as 6 bit png 90% dithered
PNG 6 bit - 90% dith. = 8.7K
balloon saved as medium quality jpeg
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.

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