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In computing, JPEG (pronounced jay-peg) is a commonly used standard method of lossy compression for photographic images. The file format which employs this compression is commonly also called JPEG; the most common file extensions for this format are .jpeg, .jfif, .jpg, .JPG, or .JPE although .jpg is the most common on all platforms.

JPEG/JFIF is the most common format used for storing and transmitting photographs on the World Wide Web. It is not as well suited for line drawings and other textual or iconic graphics because its compression method performs badly on these types of images (the PNG and GIF formats are in common use for that purpose; GIF, having only 8 bits per pixel is not well suited for colour photographs, PNG can be used to losslessly store photographs but the filesize makes it largely unsuitable for putting photographs on the web).

Jpeg: Encoding

Many of the options in the JPEG standard are little used. Here is a brief description of one of the more common methods of encoding when applied to an input that has 24 bits per pixel (eight each of red, green, and blue). This particular option is a lossy data compression method.

Jpeg: Usage

JPEG is at its best on photographs and paintings of realistic scenes with smooth variations of tone and color. In this case it usually performs much better than purely lossless methods while still giving a good looking image (in fact it will produce a much higher quality image than other common methods such as GIF which are lossless for drawings and iconic graphics but require severe quantization for full-color images).

Jpeg: Photographs

JPEG compression artifacts blend well into photographs with detailed non-uniform textures, allowing higher compression ratios. For example, a low quality photo may have a 10%, filesize or 1.7 KB; mid quality at 50% quality would be 5.7 KB in file size, and at full quality, the filesize would be 36 KB.

Jpeg: Other lossy encoding formats

Newer lossy methods, particularly wavelet compression, perform even better in these cases. However, JPEG is a well established standard with plenty of software available, including free software, so it continues to be heavily used as of 2005. Also, many wavelet algorithms are patented, making it difficult or impossible to use them freely in many software projects.

The JPEG committee has now created its own wavelet-based standard, JPEG 2000, which is intended to eventually supersede the original JPEG standard.

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