PNG (Portable Network Graphics)

PNG (pronounced ping as in ping-pong; for Portable Network Graphics) is a file format for image compression that, in time, is expected to replace the Graphics Interchange Format (GIF) that is widely used on today's Internet.

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PNG (pronounced ping as in ping-pong; for Portable Network Graphics) is a file format for image compression that, in time, is expected to replace the Graphics Interchange Format (GIF) that is widely used on today's Internet. Owned by Unisys, the GIF format and its usage in image-handling software involves licensing or other legal considerations. (Web users can make, view, and send GIF files freely but they can't develop software that builds them without an arrangement with Unisys.) The PNG format, on the other hand, was developed by an Internet committee expressly to be patent-free. It provides a number of improvements over the GIF format.

Like a GIF, a PNG file is compressed in lossless fashion (meaning all image information is restored when the file is decompressed during viewing). A PNG file is not intended to replace the JPEG format, which is "lossy" but lets the creator make a trade-off between file size and image quality when the image is compressed. Typically, an image in a PNG file can be 10 to 30% more compressed than in a GIF format.

The PNG format includes these features:

  • You can not only make one color transparent, but you can control the degree of transparency (this is also called "opacity").
  • Interlacing (see interlaced GIF) of the image is supported and is faster in developing than in the GIF format.
  • Gamma correction allows you to "tune" the image in terms of color brightness required by specific display manufacturers.
  • Images can be saved using true color as well as in the palette and gray-scale formats provided by the GIF.

Unlike the GIF89a, the PNG format doesn't support animation since it can't contain multiple images. The PNG is described as "extensible," however. Software houses will be able to develop variations of PNG that can contain multiple, scriptable images.

This was first published in September 2005

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