JPEG is a commonly used method of lossy compression for digital photography (image). The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality.
JPEG compression is used in a number of image file formats. JPEG/Exif is the most common image format used by digital cameras and other photographic image capture devices; along with JPEG/JFIF, it is the most common format for storing and transmitting photographic images on the World Wide Web. These format variations are often not distinguished, and are simply called JPEG.
The term "JPEG" is an acronym for the Joint Photographic Experts Group which created the standard. The MIME media type for JPEG is image/jpeg (defined in RFC 1341), except in Internet Explorer, which provides a MIME type of image/pjpeg when uploading JPEG images.
The compression method is usually lossy, meaning that some original image information is lost and cannot be restored, possibly affecting image quality. There is an optional lossless mode defined in the JPEG standard; however, that mode is not widely supported in products.
There is also an interlaced "Progressive JPEG" format, in which data is compressed in multiple passes of progressively higher detail. This is ideal for large images that will be displayed while downloading over a slow connection, allowing a reasonable preview after receiving only a portion of the data. However, progressive JPEGs are not as widely supported[citation needed], and even some software which does support them (such as some versions of Internet Explorer) only displays the image once it has been completely downloaded.
JPEG compression artifacts blend well into photographs with detailed non-uniform textures, allowing higher compression ratios. Notice how a higher compression ratio first affects the high-frequency textures in the upper-left corner of the image, and how the contrasting lines become more fuzzy. The very high compression ratio severely affects the quality of the image, although the overall colors and image form are still recognizable. However, the precision of colors suffer less (for a human eye) than the precision of contours (based on luminance).
Motion JPEG (M-JPEG) is an informal name for a class of video formats where each video frame or interlaced field of a digital video sequence is separately compressed as a JPEG image. Originally developed for multimedia PC applications, where more advanced formats have displaced it, M-JPEG is now used by many portable devices with video-capture capability, such as digital cameras.
M-JPEG is frequently used in non-linear video editing systems. Modern desktop CPUs are powerful enough to work with high-definition video, across the wide variation in graphics and operating-systems in use. Because it is a mature format, needs no special hardware on modern PCs, and natively offers random-access to any frame, M-JPEG support is widespread in video-capture and editing equipment.
Prior to the recent rise in MPEG-4 encoding in consumer devices, a progressive scan form of M-JPEG also saw widespread use in the "movie" modes of Digital Still Cameras, allowing video encoding and playback through the integrated JPEG compression hardware with only a software modification. Again, the resultant quality is inferior compared to a similar sized MPEG, particularly as sound (when included) was often uncompressed PCM at a low sample rate or low-compression, low processor-demand ADPCM.
Apple announced on September 1, 2010 that their newest version of the Apple TV would support Motion JPEG (M-JPEG) up to 35 Mbit/s, 1280 by 720 pixels, 30 frames per second, audio in ulaw, PCM stereo audio in .avi file format. Certain media players such as the Netgear NeoTV 550 do not support the playback of M-JPEG.
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