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Chapter 21. Creating Web Graphics > Slicing Web Graphics

Slicing Web Graphics

I'm sure you've seen many Web pages where the page is obviously chopped up into pieces and reassembled in an HTML table. Why not just make it one big image with image maps to the links? Well, here are a few reasons:

  • If you want to add graphic links, you can't do dynamic rollovers with an image map. If you want just a piece of a page to change during a rollover, that piece has to be its own slice, so it can be swapped out with another piece that represents its change of appearance during a rollover.

  • A sliced-up page can appear to display faster than waiting for one big image to download. Note that this doesn't mean it actually does appear faster. Technically, a big image is supposed to download faster than many small ones, because it takes more data to transmit many little images than one big one. (Think of it this way: Sending a ten-page letter in ten envelopes involves much more time and effort than sending all ten pages in one envelope.) However, sliced images feel faster because you see complete images faster.

  • Some images benefit from having different optimization settings applied to different parts of the image. For example, if you have a home page image containing some lines and solid areas, and a photo in the middle, the image may retain more quality after compression if the photo was compressed as a JPEG and the rest as a GIF. By slicing up the image, you can apply the optimization that's most effective for each area. By the way, this example is the one way in which a sliced version might download faster. If a big graphic contains both solid areas and photos or soft-edged areas, customizing the optimization of each slice can take the most advantage of the compression potential for the image. But it will save time on the Web only if the time saved by the optimized slices more than makes up for the time lost to the additional overhead of transmitting multiple slices.


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