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Part: VII Advanced Techniques: Scripting > Portable Network Graphics (PNG) - Pg. 394

Understanding Web Graphics 394 Figure C.12. Progressive JPEGs first appear blurry (on the left) and then clarify (on the right) as the data is received and interpreted by the browser. Portable Network Graphics (PNG) The Portable Network Graphics (PNG) format was introduced as an alternative to the GIF format. PNG supports 24-bit images and has transparency capabilities as well as antialiasing features, which allow for smooth lines. Its compression methodology makes the resulting files much smaller than GIF files. As with GIF, PNG is a lossless compression method, meaning that quality should not suffer as the image is compressed. Unlike GIF or JPEG, however, PNG supports many different bit depths and storage methods. This makes PNG extremely flexible. PNG can support RGB and grayscale images with one alpha channel--a channel of combined color data that can be used to create masks (see Hour 11, "Matting and Masks")--as a transparency mask. PNG can also support bitmap and indexed-color modes without alpha channels. PNG uses the saved alpha channel to define transparency in the file. The PNG saving options in LiveMotion are as shown here: · Indexed --Indexed PNG uses the same kind of approach to compression that GIF does, limiting the color table and producing 8-bit files. · Truecolor--This option supports the true RGB color without indexing the files. As with JPEGs, Truecolor PNGs produce 24-bit files.