Category Archives: J

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

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

JPEG 2000 (.JP2)

This is another image compression system from the Joint Photographic Experts Group (ISO/ITU-T). JPEG 2000 is very different from the original JPEG; whereas JPEG is DCT-based and examines images in a series of 8 x 8 pixel blocks, JPEG 2000 is wavelet-based using Discrete Wavelet Transform (DWT), to analyze the detail of pictures in a different way. Both coding and decoding require far more processing than JPEG, MPEG-2 or MPEG-4. Also JPEG 2000 is intra-frame only; there are no predictive frames (as in MPEG). Whereas MPEG tends to show macro blocks as it starts to fail, and the original JPEG shows ‘mosquito wings’ or ringing effects, JPEG 2000 can switch to lower data rates that can cause a softening of picture areas, which is far less noticeable. There are two file-name extensions; .JP2 is for ISO/IEC 15444-1 files and .JPX for ISO/IEC 15444-2 files.

JPEG 2000 is about twice as efficient as the equivalent I-only MPEG-2, and excels at high bit rates. It is used at up to 250Mb/s for DCI Digital Cinema applications, usually showing 24 pictures per second in 2K and 4K formats. It lends itself to a wide range of uses from portable digital cameras through to advanced pre-press and television acquisition – as well as Digital Cinema. Some favor it for use in TV distribution. The company intoPix, a specialist in JPEG 2000 technology, offers a video-over-IP solution using JPEG 2000 for HD and 4K UHD via 1Gb/s media networks with 10ms of latency. Its further technology developments are aimed at expanding the use of JPEG 2000 in TV.

See also: Compression, Compression ratio, DCT, Huffman coding, MPEG

Website: www.jpeg.org

JPEG (.JPG)

Joint Photographic Experts Group (ISO/ITU-T). It has defined many types of image compression. JPEG is a DCT-based data compression standard for individual pictures (intra-frame). It offers compression of between two and 100 times and has three levels of processing which are defined as: 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: Motion JPEG