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ARCHIVED: What is the PNG graphics file format?

Portable Network Graphics (PNG) was developed as a replacement for the GIF standard, partly because of legal entanglements resulting from GIF's use of the patented LZW compression scheme, and partly because of GIF's many limitations. PNG is superior to GIF in many ways, offering the following features:

  • Images that are the same size or slightly smaller than their GIF counterparts, while keeping lossless compression

  • Support for indexed colors, gray-scale, and RGB (millions of colors)

  • Support for 2-D progressive rendering, which is based on pixels rather than lines (as in interlaced GIFs and progressive JPEGs); this means that contents of a progressively rendered PNG file become apparent earlier in the load process

  • An alpha channel that allows an image to have multiple levels of opacity; whereas GIFs only allow a given pixel to be fully transparent or fully opaque, this feature lets you create images with degrees of transparency, better blending images with their backgrounds

  • Gamma correction, which allows you to correct for differences in how an image will appear on different computer display systems

  • File integrity checks, which help prevent problems while downloading or transferring PNG files

PNG does not support multiple images within the same image file, which means that you can't make animations with PNG, as you can with GIFs. For transmission of some types of images (e.g., true-color photographs and black-and-white images), other file formats may give better results. For more, see A Basic Introduction to PNG Features. Most graphics applications and virtually all browsers support the PNG format.

For more information, consult the PNG home page.

This is document aekl in domain all.
Last modified on January 07, 2013.

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