JPEG Lossless Compression
- JPEG Lossless Compression
"JPEG Lossless Compression" is a means of compressing images such that the original image can be recovered exactly - so called Reversible Compression. It is only commonly used in conjunction with the DICOM standard for medical imaging.
The name JPEG stands for Joint Photographic Experts Group, the name of the joint ISO/CCITT committee which created the standard. The group was organized in 1986, issuing a standard in 1992 which was approved in 1994 as ISO 10918-1, which is the same document which defined the more commonly used and well-known JPEG lossy format, but they are totally different in concept and usage.
* JPEG lossy compression is based on the discrete cosine transform (DCT) and is always lossy, even if maximum quality is used.
* JPEG Lossless compression is however based on a Pulse Code Modulation (PCM) approach, and the original images can always be constructed exactly from the compressed data.
The exact compression ratio achieved by this method depends on the noise in the original image, but for most medical images, it is in the range 2:1 to 3:1.
References
*ITU T.81 JPEG compression as [http://www.w3.org/Graphics/JPEG/itu-t81.pdf PDF] or [http://www.digicamsoft.com/itu/itu-t81-1.html HTML]
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