Lossless JPEG
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The Joint Photographic Experts Group, in addition to their well-known lossy image compression techniques, JPEG and JPEG 2000, also have three standards for lossless compression (of which JPEG-LS has a lossy mode):
Lossless JPEG was developed as a late addition to JPEG in 1993, using a completely different technique from the lossy JPEG standard. It uses a predictive scheme based on the three nearest (causal) neighbors (upper, left, and upper-left), and entropy coding is used on the prediction error. It is not supported by the standard Independent JPEG Group libraries, although Ken Murchison of Oceana Matrix Ltd. wrote a patch that extends the IJG library to support Lossless JPEG. Lossless JPEG has some popularity in medical imaging, and is used in DNG and some digital cameras to compress raw images, but otherwise was never widely adopted.
JPEG-LS was developed with the aim of providing a low complexity "near lossless" image compression standard that could be able to offer better compression efficiency than lossless JPEG. Part 1 of this standard was finalized in 1999; and when released, Part 2 of this standard will introduce extensions such as arithmetic coding. The core of JPEG-LS is based on the LOCO-I algorithm, that relies on prediction, residual modeling and context-based coding of the residuals. Most of the low complexity of this technique comes from the assumption that prediction residuals follow a two-sided geometric distribution (also called a discrete Laplace distribution) and from the use of Golomb-like codes, which are known to be approximately optimal for geometric distributions. Besides near lossless compression, JPEG-LS also provides a lossy mode where the maximum absolute error can be controlled by the encoder. Compression for JPEG-LS is generally much faster than JPEG 2000 and much better than the original lossless JPEG standard.
JPEG 2000 includes a lossless mode based on a special integer wavelet filter (biorthogonal 3/5). JPEG 2000's lossless mode runs more slowly and has often worse compression ratios than JPEG-LS on artificial and compound images[1][2]. JPEG 2000 fares better than the UBC implementation of JPEG-LS on digital camera pictures[citation needed]. JPEG 2000 is also scalable, progressive, and more widely supported.
[edit] External links
- JPEG 2000 still image coding versus other standards
- JPEG2000, JPEG-LS and other lossless codecs on greyscale images
- JPEG-LS home page
- LOCO-I home page
- Licensing terms for HP's LOCO technology in JPEG-LS (free reg. req.; not sublicensable; available only to companies)
- Links to Various Implementations
- Single-tone/grayscale JPEG-LS encoder algorithm
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![[1]](http://www.jpeg.org/public/wg1n1816.pdf){kind=link}
