and better looking results. Achieving photo-real results requires careful planning from the shoot and computer imagery through to compositing in post production. Excellence in keying, so there are no telltales of blue screen haloes or color spill, are among the many techniques required for successful results. See also: Compositing, Digital keying

Pixel (or Pel) A shortened version of ‘Picture cell’ or ‘Picture element’. The name given to one sample of picture information. Pixel can refer to an individual sample of R, G, B, luminance or chrominance, or sometimes to a collection of such samples if they are co-sited and together produce one picture element. See also: Aspect ratio – of pixels, Sub-pixel

PLD

Programmable Logic Device. This is a family of devices that has included PROMs (Programmable Read Only Memories), PLAs (Programmable Logic Arrays) and PALs (Programmable Array Logic). Today FPGAs (Field Programmable Gate Arrays) are the main interest. These range in size and complexity from a few dozen up to millions of gates to provide a compact and efficient means of implementing complex non-standard logic functions. See also: Moore’s Law

Plug-in

Software, usually from a third party, that brings added functionality to a computer application. For post production this may add highly specialized aspects to digital effects.

POTS

Plain Old Telephone Service. This is the analog connection that many people still speak on, or connect their modems or fax machines to. Its applications have gone far beyond its initial aims.

Printer lights The illumination used to expose film in a processing laboratory. ‘White’ light is passed through red, blue and green filters so that the exposure to each can be individually controlled. Film is contact printed, placing the new film stock against the processed film that carries the images. The amount of light can be varied to provide the required exposure to show more detail in the highlights or the shadows or to keep to the mid-range of the scene brightness. To print an overexposed negative will require higher values and underexposed lower values of printer lights. A change of 1 in the value represents 1/12th of a stop adjustment in exposure. Differential adjustments of the values provides basic color correction (timing). The values for the lights are recorded as grading (timing) numbers onto disk or paper tape. See also: Color timing, Film Basics (Tutorial 2), One-light pass, Timing

Print film

Film stock designed specifically for distribution and exhibition at cinemas. Unlike negative film, it is high contrast and low on latitude. This is designed to give the best performance when viewed at cinemas. Obviously a release print has to be clear of the orange base so this is bleached out during processing. See also: Film basics (Tutorial 2)

Profile See MPEG-2

Progressive (scan) Method of scanning lines down a screen where all the lines of a picture are displayed in one continuous vertical scan (progression). There are no fields or half pictures as with interlace scans. Progressive scanning is becoming far more common as it is used with computer displays and all panel displays – LCD and Plasmas, and is now starting to be used for some DTV formats, e.g. – 1080/24P, 720/60P. The ‘P’ denotes progressive. A high picture refresh rate is required to give good movement portrayal, such as for fast action and camera pans. For television applications using progressive scanning, this implies a high bandwidth or data rate and high scanning rates on CRT displays. Progressive scanning does not show the dither of detail associated with interlaced scans. See also: 24P, Interlace, Interlace Factor

Projectors (digital)

Digital projectors input digital images and project them onto cinema-sized screens. Huge advances in this technology in recent years have been one of the driving forces behind digital cinema. For post production or DI, many houses offer big screens for customers to see what the final cinema experience will look like. With resolutions up to 4K, the viewing public is very impressed with the results as, without film’s scratches, dirt and weave, they are treated to consistent high quality results. Combined with suitable digital cinema players some projectors can sequentially display the left and right-eye images of stereo movies for a 3D film experience. See also: Color management, Digital Cinema, DLP, D-ILA, SXRD

Pseudoscopic (Stereoscopic) If a stereoscopic signal is reversed (e.g. each eye is being fed the opposite eye signal) a strange ‘punched in’ effect appears. This is also referred to as inverted stereo or reversed stereo.

Publishing See Deliverables Pulfrich effect (Stereoscopic)

Horizontal motion that can be interpreted as binocular depth. A stereo effect which is produced when 2D images moving laterally on a single plane are viewed at slightly different times by each eye.

Purpose-built hardware

Hardware and software built for a specific task (e.g. a DVE), not general purpose (computer). Purpose-built hardware is able to provide much improved processing speeds, between 10 and 100 fold, over systems using the same technology applied to general-purpose architecture and operating system software.

Quantization

Factor applied to DCT coefficients as a part of the process of achieving a required video compression. The coefficients relating to the least noticeable aspects of picture detail – e.g. high frequencies with low amplitude – are progressively reduced so that the final data will fit into the specified data file space. This space is often fixed and relates directly to the quoted compression ratio for I-frame only schemes such as DV. Note that the required quantization will vary according to scene content. Given that too much data would cause problems by overflowing the allotted capacity of the file, compression schemes are cautious and designed to undershoot the file limit. To what extent the files are filled is a measure of the quality of a compression scheme – a reason why the quoted ‘compression ratio’ does not tell the whole story.

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GLOSSARY OF TERMS