NG (pronounced "ping") is a new type of graphics format for images. It is an extensible file format for the lossless, portable, well-compressed storage of raster images. Raster images are digital images created or captured (for example, by scanning in a photo) as a set of samples of a given space. A raster is a grid of x-(horizontal) and y-(vertical) coordinates on a display space (And for three-dimensional images, a z-coordinate). A raster image file identifies which of these coordinates to illuminate in monochrome or color values. The raster file is sometimes referred to as a bitmap because it contains information that is directly mapped to the display grid. A raster file is usually difficult to modify without loss of information. PNG was developed in 1995 and in time is expected to replace the popular GIF format that is widely used on today's Internet.

L i c e n s i n g
The GIF format patented by Compuserve (now owned by America Online), 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 Compuserve.) The PNG format, on the other hand, was developed by an Internet committee expressly to be patent and license-free. In fact, PNG was approved as a standard by the World Wide Web consortium to replace GIF because GIF uses a patented data compression algorithm called LZW.

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Note: The most recent versions of Netscape Navigator and Microsoft Internet Explorer now support PNG.

PNG was designed to be:

• Simple and Portable   Developers should be able to implement PNG easily.
• Legally Unencumbered   PNG is freely open to the public. To the best knowledge of the PNG authors, no algorithms under legal challenge are used. (Some considerable effort has been spent to verify this.)
• Well Compressed   Both indexed color and true color images are compressed as effectively as in any other widely used lossless format, and in most case more effectively.
• Interchangeable   Any standard conforming PNG decoder must read all conforming PNG files.
• Flexible   The format allows for future extensions and private add-ons, without compromising interchangeability of basic PNG.
• Robust   The design supports full file integrity checking as well as simple, quick detection of common transmission errors.

   Robustness against transmission errors has been an important consideration. For example, images transferred across Internet are often mistakenly processed as text, leading to file corruption. PNG is designed so that such errors can be detected quickly and reliably.

Since GIF is no longer freely usable, because CompuServe patents it and no other commonly used format can directly replace it, plus, the creation of a new format over GIF would provide improvements. It was an excellent opportunity for creators to design a new format that fixes some of the known limitations of GIF. The creators of PNG might have used an adaptation of an existing format, for example GIF with an unpatented compression scheme. But this would require new code anyway and it would not be all that much easier to implement than a whole new file format.

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