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The Portable Network Graphics file format, commonly referred to as PNG, is an image format similar to the popular GIF format. It is pronounced either as the word 'ping' or, more commonly, spelled out as 'P-N-G.'
The PNG image format was developed in response to the enforcement of a patent on the pervasive GIF format. GIF images were ubiquitous in the early 1990s, having spread throughout the nascent web and bulletin board systems after CompuServe's debut of the format in 1987. In 1995, the Unisys company announced that they would begin enforcing their patent of the GIF image format for software made for profit. PNG was developed as a royalty-free alternative to GIF soon after this announcement. In 2003, the US patent for the GIF image format expired, leaving it royalty-free as well.
In addition to the now-obsolete benefit of being royalty free, the PNG image format has a number of technical advantages over the GIF format.
Images saved in the PNG image format potentially have a much higher color depth than their GIF counterparts —- while GIF limits its palette to 256 colors, PNG can be true color. This allows for a much higher fidelity of image than GIFs are capable of, allowing for images on a par with their JPEG cousins.
Images in the PNG image format are also smaller than their GIF counterparts, though the higher color depth often results in larger files and the misconception that PNG is a bulkier format. Actually, if one forces a PNG to save in 256 colors, the file will nearly always be smaller than a GIF file of the same quality.
The PNG image format also allows for an alpha channel, providing transparency options that are not available in any other common image format. This transparency is, unfortunately, not supported by Internet Explorer, making its use as a web tool limited.
It should be noted that unlike the GIF format, the PNG image format does not support animation. Related formats (APNG and MNG) exist which do handle animation in a similar manner to the GIF format.
The PNG image format has a strong core following, even in the absence of patent issues to support its existence. It has suffered because of a lack of full support in Internet Explorer, but continues to offer a robust alternative to the two more common image formats of GIF and JPEG. With mainstream graphics programs such as Fireworks and Photoshop offering strong support for the PNG image format, along with its readily apparent technical superiority to the GIF format, it is likely that the popularity of PNG will only increase.