data is under the replay head. As disk diameters have decreased so rotational (spindle) speeds have tended to increase but there is still much variation. Modern 3.5-inch drives typically have spindle speeds of between 7,200 and 10,000 RPM, so one revolution is completed in 8 or 6 ms respectively. This is represented in the disk specification as average latency of 4 or 3 ms. It is reduced to 2 ms in the faster drives operating at 15,000 RPM.
Latitude
A B C D E F G H I J
K L
M N O P Q R S T U V
W X Y Z
Latitude is the capacity of camera negative film (especially) to hold information over a wider brightness range than is needed for the final print. This provides a degree of freedom that is needed because it is impossible to see if the exposure is totally correct until the film comes back from the laboratory – long after the set has been struck and everyone has gone home. Latitude provides room for later adjustment in printing to compensate for over or under exposure. This contrasts with using digital cinematography where it is possible to see the results immediately and make any required adjustment at the shooting stage. This procedure can reduce the need for a very wide latitude (which cannot extend to the release prints) by ensuring the lighting and camera set ups are always correct at the shoot. See also: Camera negative
Layer(ing)
A collection, or ‘pack’ of clip layers can be assembled to form a composite layered clip. Layers may be background video or foreground video with their associated matte run. The ability to compose many layers simultaneously means the result can be seen as it is composed and adjustments made as necessary.
LCOS Liquid Crystal On Silicon – an imaging chip technology that has been likened to a cross between LCD and DLP. Like LCDs this uses one liquid crystal per pixel to control the light, but whereas LCD is transmissive, the light travels through the crystals, LCOS is reflective, like DLP. LCOS is the basis for many imagers, JVC’s implementation is D-ILA and Sony’s SXRG appear to use similar some ideas – though many refinements are used. See also: 14:9, Anamorphic, ARC
Level
See MPEG-2 Lights
See Printer lights
Linear (editing) The process of editing footage that can only be accessed or played in the sequence recorded. Tape and film are linear in that they have to be spooled for access to any material and can only play pictures in the order they are recorded. With spooling, jogging and pre-rolls, so called ‘mechanical considerations’, absorbing upwards of 40 percent of the time in a VTR edit suite, linear editing is slow for everyday editing. The imposition of having to record items to an edit master tape in sequence limits flexibility for late adjustments: e.g. inserting shots between existing material may involve either starting the job again or re-dubbing the complete piece. See also: C-mode, Digital disk recorder, True random access
Letterbox
A method used to show higher aspect ratio (e.g. 16:9) images on a low aspect ratio (e.g. 4:3) display. While all the contents of the pictures can be seen there are strips of (usually) black above and below the picture which some people do not like.
Linear (keying)
In linear keying the ratio of foreground to background pictures at any point on the screen is determined on a linear scale by the level of the key (control) signal. This form of keying provides the best possible control of key edge detail and anti-aliasing. It is essential for the realistic keying of semi-transparent effects such as transparent shadows, through-window shots and partial reflections. See also: Keying
LSB
See Digit LTC
Longitudinal Timecode. Timecode recorded on a linear track on tape and read by a static head. This can be easily read when the tape is moving forwards or backwards but not at freeze frame – when VITC, timecode recorded with the picture material, can be used. See also: VITC
LTO-2, LTO-3 Data storage formats from Quantum using linear, not helical, recording technology. Used for data archive and transfer, these perform lossless compression on the data and are currently quoted as storing up to 800GB on a single tape cartridge and replay at up to 245 GB/h – based on a 2:1 lossless compression ratio. See also: DTF, SAIT-2 Website: www.
quantum.com
Luminance
A component of video: the black and white or brightness element, of an image. It is written as Y, so the Y in Y,B-Y,R-Y, YUV, YIQ and Y,Cr,Cb is the luminance information of the signal. In a color TV system the luminance signal is usually derived from the RGB signals, originating from cameras or telecines, by a matrix or summation of approximately: Y = 0.3R + 0.6G + 0.1B (based on ITU-R BT.601) See also: Coded, RGB, Y (B-Y) (R-Y), Y,Cr,Cb, YUV LM LUT Look-up table. This is a table of multipliers used to convert values from one type of digital scale to another. The LUT will contain a distinct multiplying value for every input digital value. For example, a LUT can be used to convert brightness values measured by an electronic sensor, which will be linear, to logarithmic values which more accurately reflect our perception – and the way film responds to light. As modern post production equipment is expected to work across media – film, TV, DVD, D-cinema, etc., there is increasing need for conversions using LUTs to suit differences in color space between display systems (CRTs, DLPs, etc.) as well as in the media themselves. A 1D LUT maps one input value to a new output value; gamma changes can be implemented with a 1D LUT. A 3D LUT maps three input values to a new output value. 3D LUTs are widely used for print matching and X’Y’Z’ colorspace transforms where the output of, say, the R value depends on the input R, G and B values. Thus three 3D LUTs are required for full colorspace transforms. See also: Color cube
Macroblock See MPEG-2
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GLOSSARY OF TERMS
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