MACROMEDIA FIREWORKS MX 2004-USING FIREWORKS Use Manual page 241

Making areas transparent
You can set transparent areas for GIFs and 8-bit PNGs so that in a web browser the background
of the web page is visible through those areas. In Fireworks, a gray-and-white checkerboard on
document previews denotes transparent areas.
Optimized image preview in Fireworks; image exported with transparency and placed on a web page
with a colored background
Note: 32-bit PNGs automatically contain transparency, though you won't see a transparency option
for 32-bit PNGs in the Optimize panel.
You should use index transparency when exporting GIF images that contain transparent areas.
With index transparency, you set specific colors to be transparent upon export. Index
transparency turns on or turns off pixels with specific color values. Because GIFs support index
transparency, it is the most common form of transparency used on the web.
Note: GIF images are exported without transparency by default in Fireworks. Even if the canvas
behind an image or object appears transparent in Original view in Fireworks, this does not mean that
the background for that image will be transparent when you export it as a GIF for use on the web. You
must choose Index Transparency before export.
You can also use alpha transparency, although it is not often used with web graphics because only
PNGs support it and most web browsers do not support PNG format. Alpha transparency is
often used in exported graphics that contain gradient transparency and semi-opaque pixels. Alpha
transparency is also useful for exporting files to Macromedia Flash or Director, because both
applications support this type of transparency.
Note: Setting colors to transparent affects only the exported version of the image, not the actual
image. You can see what the exported image will look like in a preview. For information about the
document preview buttons, see "Previewing and comparing optimization settings" on page 233.
Optimizing in the workspace 241