for 1125/60 and 1250/50 (1035 and 1152 active lines) HDTV formats defining values and a ‘4:2:2’ and ‘4:4:4’ sampling structure that is 5.5 times that of ITU-R BT.601. Note that this is an ‘expanded’ form of 601 and so uses non-square pixels. See also: Common Image Format IJ ITU-R/BT.799 See Dual link

iTV See: Interactive Television

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

Keycode

A machine-readable barcode printed along the edge of camera negative film stock outside the perforations. It gives key numbers, film type, film stock manufacturer code, and offset from zero-frame reference mark (in perforations). It has applications in telecine and film scanning for accurate film-to-tape or data transfer and in editing for conforming neg. cuts to EDLs.

Keyframe

A set of parameters defining a point in a transition, e.g. of a DVE effect. For example a keyframe may define a picture size, position and rotation. Any digital effect must have a minimum of two keyframes, start and finish, although complex moves will use more – maybe as many as 100. Increasingly, more parameters are becoming ‘keyframeable’, i.e. they can be programmed to transition between two, or more, states. Examples are color correction to make a steady change of color, and keyer settings, perhaps to make an object slowly appear or disappear. See also: DVE

Keying

The process of selectively overlaying an area of one picture (or clip) onto another. If the switch between the overlaid and background pictures is simply ‘hard’ this can lead to jagged edges of the overlaid, or keyed, pictures. They are usually subjected to further processing to produce ramped, slightly soft, key edges to give a cleaner, more convincing, result. The whole technology of deriving key signals from image data and the color corrections applied to keyed image edges, has greatly expanded through the use of digital technology, so that many operations may be used together, e.g. softening the key, color correcting key spill areas, and much more. See also: Chroma keying, Digital keying, Linear keying

Keystoning (Stereoscopic)

The result arising when the film plane in a camera or projector is not parallel to the view or screen, leading to a trapeze shape. On a stereoscopic image, where the cameras are ‘toed-in’ so that the object of interest coincides when viewed, there can be some mismatching of the outlines or borders of the two images. Techniques like corner pinning can be used to help correct this.

KLV KLV is a data encoding protocol (SMPTE 336M). The Key is a unique, registered sequence of bits that defines the type of content that is coming (video, audio, EDL, etc) and Length – number of bytes ahead of Value, the content ‘payload’ itself. Compliance to KLV means that a wider range of equipment and applications can understand each other’s files. See also: AAF, MXF

LAD

Laboratory Aim Density is a quality control method to maintain consistency in film prints. To aid in color timing, original negatives are timed relative to a LAD Control Film which includes reference patches and a figure of a girl (Marcie). There are differing LAD values for each type of print or duplication film that the original will be printed on.

Latency (of data) The delay between requesting and accessing data. For disk drives it refers to the delay due to disk rotation only – even though this is only one of several factors that determines time to access data from disks. The faster a disk spins the sooner it will be at the position where the required

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GLOSSARY OF TERMS