MACROMEDIA FLASH 8-USING FLASH Use Manual page 474

4.
Select a bit depth to set the number of bits per pixel and colors to use in creating the image:
Select 8-bit for a 256-color image.
Select 24-bit for thousands of colors.
Select 24-bit with Alpha for thousands of colors with transparency (32 bits).
The higher the bit depth, the larger the file.
5.
Select one of the following options to specify appearance settings for the exported PNG:
Optimize Colors
reduces the file size by 1000 to 1500 bytes without affecting image quality but increases
the memory requirements slightly. This option has no effect on an adaptive palette.
Interlace incrementally shows the exported PNG in a browser as it downloads. Interlacing
lets the user see basic graphic content before the file has completely downloaded and
might download the file faster with a slow network connection. Do not interlace an
animated PNG file.
Smooth
applies anti-aliasing to an exported bitmap to produce a higher-quality bitmap
image and improve text display quality. However, smoothing might cause a halo of gray
pixels to appear around an anti-aliased image placed on a colored background, and it
increases the PNG file size. Export an image without smoothing if a halo appears or if
you're placing a PNG transparency on a multicolored background.
Dither Solids
applies dithering to solid colors and gradients. For more information, see
Dither options in step 6.
Remove Gradients
application to solid colors using the first color in the gradient. Gradients increase the size
of a PNG and are often poor quality. If you use this option, select the first color of your
gradients carefully to prevent unexpected results.
6.
If you selected 8-bit for Bit Depth in step 4, select a Dither option to specify how pixels of
available colors are mixed to simulate colors not available in the current palette. Dithering
can improve color quality, but it increases file size. Select from the following options:
None turns off dithering and replaces colors not in the basic color table with the solid
color from the table that most closely approximates the specified color. Turning dithering
off can produce smaller files but unsatisfactory colors.
Ordered provides good-quality dithering with the smallest increase in file size.
Diffusion
provides the best-quality dithering but increases file size and processing time. It
also works only with the web 216 color palette selected.
474 Publishing
removes any unused colors from a PNG file's color table. This option
, which is turned off by default, converts all gradient fills in the