Portable Network Graphics (PNG) was designed as a replacement for the GIF format in order to avoid infringement of Unisys' patent on the LZW compression technique.

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Although it took time for the PNG format to be supported, new web browsers support the PNG format and GIF images can usually be replaced by PNG images if desired. However, Internet Explorer versions 6 and earlier do not support PNG's alpha channel transparency feature without using Microsoft-specific HTML extensions.[17] Using standard HTML <img> tags for PNG images in Internet Explorer can produce a look different from that intended. Internet Explorer 7 supports alpha channel transparency without needing extensions.[18]

There have been claims that PNG files are generally larger than GIFs.[citation needed] PNG files can indeed be much larger than GIF files in situations where a GIF and a PNG file were created from a high-quality master image, as PNG is capable of storing more color depth and transparency information than GIF. However, identical 8-bit (or lower) image data rendered in PNG and GIF formats should yield similar sizes. Misinformation about PNG efficiency can generally be traced back to poor PNG support in older versions of some image manipulation programs, (for example Adobe Photoshop did not optimize PNGs for reduced color palettes by default). [citation needed]MNG, a variant of PNG that supports animation, reached version 1.0 in 2001, but few applications support it. Animated GIF remains widely used as many applications are capable of creating the files, and it remains the only animated image format capable of being rendered in nearly all modern web browsers without the use of a plug-in.[citation needed] Nevertheless, embedded Flash objects, MPEGs and other video formats are used in place of animated GIFs in many websites. Other approaches, such as individual frames served by AJAX, or SVG images may be animated via JavaScript. In 2004, a proposed extension to the PNG format called APNG was suggested. It was to provide the ability to animate PNG files, while retaining backwards compatibility in decoders that cannot understand the animation chunk. Older decoders would simply render the first frame of the animation.