Game Development Reference
Figure 6.4 A character
sequence of individual PNG
files, with Onion Skinning
turned on in Flash.
8-BIT PNGs WITH AN ALPHA CHANNEL
PNGs come in two flavors: 32 bit (or 16 million colors with a full 8-bit
alpha channel) and 8 bit (256 colors). A seemingly little known fact about
Adobe Fireworks is that it can generate a special type of PNG, which has
an 8-bit color channel and an 8-bit alpha channel (sometimes called
PNG8+8). If you
re using artwork that has a fairly flat color palette or that
t degrade when the number of colors is reduced, this format is an
outstanding option. It allows you to keep nice clean edges and transpar-
ency, thanks to a true alpha channel while reducing the file size by over
50%. In fact, this format is often smaller than the compressed version of
a 32-bit PNG inside of Flash, and the resulting images look better.
Hopefully, this format will eventually find its way into Photoshop
For Web feature. Until then, you can always use Fireworks to batch process
your 32-bit PNGs to 8-bit PNGs.
Of course, these are just guidelines, not hard-and-fast rules, but
using a combination of formats that take file size into account up
front will save you time in the optimization phase. Another aspect
of dealing with raster images is how Flash will handle them when
compiling the game. Flash has a couple of different options when
it comes to exporting images that can have an impact on how your
game looks. Simply double-click on an image in your library to
view its properties. You can also select multiple images at a time
and adjust the properties of all of them at once.
When you import a JPEG file that has already been optimized in
another application, Flash will use it
by default. But in case of
PNGs, if the image has 256 colors or less, Flash will automatically