JPEG
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Overview
JPEG (pronounced JAY-peg, standing for Joint Photographic Experts Group) 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 itself specifies only how an image is transformed into a stream of bytes, but not how those bytes are encapsulated in any particular storage medium. A further standard, created by the Independent JPEG Group, called JFIF (JPEG File Interchange Format) specifies how to produce a file suitable for computer storage and transmission (such as over the Internet) from a JPEG stream. In common usage, when one speaks of a "JPEG file" one generally means a JFIF file, or sometimes an Exif JPEG file. There are, however, other JPEG-based file formats, such as JNG, and the TIFF format can carry JPEG data as well.
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 usually produce much better results for such images than, for example, GIF, which can be lossless only if the image contains 256 or fewer unique colours.
It should NOT be used for images containing text, such as menus or headings, as the compression method used tends to blur sharp edges, making text difficult to read. GIF or PNG files are a better choice for these types of images.
JPEG compression artefacts blend well into photographs with detailed non-uniform textures, allowing higher compression ratios.
Quality examples
The mid-quality photo uses only one sixth the storage space but has little noticeable loss of detail or visible artefacts. However, once a certain threshold of compression is passed, compressed images show increasingly visible defects.
See also
External links
- Wikipedia JPEG Article - http://en.wikipedia.org/wiki/JPEG
| Common web-based image formats |
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| GIF | JPEG | PNG |
Categories: Merge | Web Design | Images
