MACROMEDIA FIREWORKS 2, Use Manual

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Importing and Exporting 105
PNG
The Portable Network Graphic, or PNG, is the most
versatile of the web graphic formats. However, not all
web browsers can take full advantage of PNG
characteristics. A PNG supports up to 32-bit color, can
contain transparency or an alpha channel, and can be
progressive.
Web format comparison
Compression
PNG compression is lossless, even in high color depths.
It compresses across rows and columns of pixels, yielding
better compression than GIF, which only scans rows. A
PNG can compress more than a GIF or JPEG of the
same color depth and quality.
The PNG format is best suited for creating complex live
transparency, high-color graphics, or better compressed
low-color graphics.
GIF JPEG PNG
Color depth 8-bit maximum Up to 24-bit Up to 32-bit
Compression Lossless; compresses
solid areas of color Lossy; compresses subtle
color transitions Lossless
Transparency support Yes No Yes
Advantages Lossless compression
Transparency Ability to control quality
loss in compression
Excellent compression of
photographic images Lossless compression
Alpha transparency
High color support
Disadvantages Maximum of 256 colors
Does not compress
gradient colors well No transparency
Loss of quality when
compressed Not completely
supported by common
browsers without using
plug-ins
Typical Uses Cartoon images
Logos
Animated banners Scanned photographs
Images with complex
textures
Images with complex
gradient colors Images with high
numbers of colors
Complex, live
transparency