Java A general purpose programming language developed by Sun Microsystems and best known for its widespread use in animations on the World Wide Web. Unlike other software, programs written in Java can run on any platform type, so long as they have a Java Virtual Machine available. Website: java.sun.com
JPEG (.JPG) Joint Photographic Experts Group (ISO/ITU-T). They have defined a compression known as JPEG which is a DCT-based data compression standard for still pictures (intra-frame). It offers compression of between two and 100 times and three levels of processing are defined: the baseline, extended and lossless encoding. JPEG baseline compression coding, which is overwhelmingly the most common in both the broadcast and computer environments, starts with applying DCT to 8 x 8 pixel blocks of the picture, transforming them into frequency and amplitude data. This itself may not reduce data but then the generally less visible high frequencies can be divided by a high 'quantizing' factor (reducing many to zero), and the more visible low frequencies by a much lower factor. The 'quantizing' factor can be set according to data size (for constant bit rate) or picture quality (constant quality) requirements - effectively adjusting the compression ratio. The final stage is Huffman coding which is lossless but can further reduce data by 2:1 or more. Baseline JPEG coding creates .jpg files and it is very similar to the I-frames of MPEG, the main difference being they use slightly dissimilar Huffman tables. See also: Compression, Compression ratio, DCT, Huffman coding, MPEG Website: www.jpeg.org
JPEG 2000 (.JP2) This is an image coding system that is totally different from the original JPEG as it is based on different principles. Whereas JPEG is DCT-based and examines images in a series of 8 x 8 pixel blocks, JPEG 2000 is wavelet-based - analyzing pictures in circular areas. Both coding and decoding require far more processing than MPEG-2 and MPEG-4. Also JPEG 2000 is intra-frame only, there are no predictive frames (as in MPEG). Whereas MPEG tends to show blocks as it fails, and the original JPEG shows 'mosquito wings' or ringing effects, JPEG 2000 knows nothing of blocks and a failure, running out of data space, can cause a softening of picture areas, which is far less noticeable. (See page 18) Website: www.jpeg.org
JBOD Just a bunch of disks. This could be a collection of disk drives connected on a single data bus such as SATA, Fibre Channel or SCSI. JBODs are cheap and can offer large volumes of storage that may be shared among their users. As there are no intelligent controllers, items such as data speed and protection may well be compromised. See also: SAN