Category Archives: P

Pack

A set of clips, mattes, DVE settings, color corrector, keyer, etc., that are used together to make a video layer of a composited picture. Quantel equipment allows packs to be saved and archived so they can be used later for any re-works.

PAL

Phase Alternating Line. The analog color coding system, which effectively compressed three TV frames of red, green and blue sent from the camera or scanner, into one whole color picture. It was widely used for television in Europe and in many countries around the world, always with the 625/50 (lines per picture/interlaced fields per second) system, except in Brazil (see PAL-M). The engineers designing PAL had the advantage of seeing the NTSC system, and managed to improve on it but by swinging the phase of the reference color ‘burst’ on alternate lines, hence Phase Alternating Line. NTSC had no way of automatically correcting the drift of its subcarrier that carried the color information. So, as the phase drifted, so did did the color’s hue. Hence the system’s other name ‘Never Twice the Same Color’! As PAL switched the subcarrier phase by 90-degrees line by line (+45 and -45 from the color axis), the phase and so the hue of the colors, could be averaged, so rendering the correct hue at the receiver. This required every decoder to have a one TV-line delay, which was expensive. However the price quickly dropped as sales took off in the mid 1960s.

Bandwidth for the PAL-I system (here ‘I’ indicates 625/50 line/field scanning) is typically 5.5 MHz luminance, and 1.3 MHz for each of the color difference signals, U and V which are coded with the luminance. Note that the PAL term is frequently used to describe any 625/50I analog format even if it is component, or in the 576/50I digital television system where PAL coding is not used.

PAL-M

A version of the PAL color coding system, but using a 525-line 60-field structure. It was only used in parts of South America (Brazil).

PAM

Production Asset Management could be considered as a subset of MAM It is intended to co-ordinate the work of all stages involved with post production, and so ensure it runs efficiently and meets planned deadlines and budgets. It can enhance collaboration and manage down to a detailed level for edit suites and media storage, and manage those contributing other elements, such as special effects. Management of items such as the original video, audio, EDLs, proxies, versioning, content protection, backup, can be included. But PAM is not tightly defined and some say that it ends when the media file is ‘flattened’, with all the effects, corrections, cuts, mixes, etc, are applied and resolved to produce one layer of video and the finished tracks of audio.

PAN

Personal area network used for communicating between computer-based devices, such as phones, mobile TVs and PDAs as well as fixed computers, all within a few meters, and through to other networks such as the Internet. PANs can be wired, via busses such as USB or IEEE 1394, or wireless (WPAN) using technologies such as Bluetooth.

Parallax (Stereoscopic)

This refers to the separation of the left and right images on the projection device or display screen. Positive Parallax puts an object behind the screen (on screen objects in the left eye image are to the left of the same objects in the right eye image). Negative parallax puts an object in front of the screen (on screen objects in the left eye image are to the right of the same objects in the right eye image).

Zero or neutral parallax puts an object on the screen (on screen objects in the left eye image are overlaid on the same objects in the right eye image).

The only difference between stereo cameras should be parallax or angle between the axes of the lenses, as in Camera Convergence – anything else can disturb the stereo viewing experience. This requires close attention, so that the cameras are set-up the same and with the same filters. Color differences, skewing, vertical misalignment, differential weave and hop, lens flares, poor VFX fixes, scratches and dirt can all cause problems.

Fast cuts between shots with strong positive and strong negative parallax can be unsettling in some circumstances. This is because the eyes and brain are being asked to jump uncomfortably quickly between positions and then make sense of the result. This can be mitigated by the use of ‘handing off’ – dynamically changing the convergence of an outgoing shot in relation to an incoming shot. Another method of dealing with this is trying wherever possible to cut between shots that are somewhat close in parallax.

Vertical parallax is a vertical offset between stereo images and is very uncomfortable to watch – so it is necessary to remove it during post production if there has been camera misalignment during shooting.

Note: The term ‘Parallax’ is sometimes used interchangeably with ‘Congruence’ or ‘Disparity’.

Parallel processing

Using several processors simultaneously with the aim of increasing speed over single processor performance. It often refers to array processor computer hardware that carries out multiple, often identical, mathematical computations at the same time. Generally array processors are designed with specific tasks in mind and so are not suitable for running complex operational software. Due to system administration and the fact that not all processors will complete their tasks at the same moment, causing waiting time, the increase in speed gained by sharing the task may not be proportional to the number of channels available.

Due to the very different structure of a parallel processing computer, software designed to run on a single processor system may well need significant changes to take full advantage of a parallel system. The current expansion of popular PC CPUs to offer two, four or more processor CPUs generally works with established applications by running the various applications on separate core processors, rather than one application on multiple processors.

PCI Express

This data interface is widely available on PCs. Unlike its predecessor PCI interfaces, PCIe provides fast serial connections which are more reliable for handling fast data than the parallel connections used with previous PCIs. A range of cards offer 1, 4, 8 or 16 full duplex (same speed both ways) data ‘lanes’. These are written as 1x, 4x, etc. A larger 32-lane card is available but rarely used. The cards are hot swappable.

PCIe is commonly used to connect storage such as optical and hard discs and SSD drives. The available data speed has increased over three versions so v3.0 offers a data speed up to 985 MB/s per lane.

See also: www.hardwaresecrets.com

Perf film

Short for perforations. It is a way to describe some information about the format of images on 35mm film by how many of the perforations, or sprocket holes, are used per image. For example, Full Frame is 4 perf.

Photo-real

Video and film effects that are constructed in such a way that they look totally real, and not synthetic, are referred to as photo-real effects. This use of effects has rapidly increased and so changed the way many productions are shot and post produced – leading to lower budgets and better looking results.

Achieving photo-real results requires careful planning from before the shoot and computer imagery through to compositing in post production. Excellence in keying, so there are no telltales of blue screen halos 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. They are widely used in Quantel equipment where FPGAs also offer a fast track for the implementation of new improvements and ideas.

See also: Moore’s Law

Plug-in

Software, usually from a third party, that brings more functions 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.

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)

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

Professional Disc (PFD)

Sony’s name for their Blue Laser disk technology used in XDCAM products and for data recording. This has many similarities to the Blu-ray disk, with CD/DVD dimensions it is housed in a cartridge, weighs 90g and offers 23.3 GB storage on one-side and a data rate of 9 MB/s (72 Mb/s). It can support 70 minutes of 50 Mb/s MPEG IMX and faster-than-realtime transfers. Good for around 10,000 re-record cycles it is more compact, faster and more versatile than tape.

Further development has produced a dual-layer model with 50 GB, then a triple with 100 GB and a quad version with 128 GB, providing up to four hours of recording.

See also: Optical disks

Progressive (scan)

Method of scanning lines down a screen where all the lines of a picture are displayed in one continuous vertical scan (progression), 1, 2, 3, 4… etc. There are no fields or half pictures as with interlace scans. Progressive scanning has become more common as it is used with computer displays and all panel displays – LCD, LED and Plasmas, and is used in television formats, e.g. – 1080/24P, 720/60P, 1080/30P… The ‘P’ denotes progressive. A high picture refresh rate is required to give good movement portrayal, such as for fast action sports and camera pans. Higher frame rates such as 1080/50P 1080/60P are in use; they require infrastructure capable of 3 Gb/s, known as 3G SDI. With ITU-R Recommendation BT.2020 for UHDTV standards describing only progressive scans for its 4K and 8K formats, it looks as though the future is progressive.

It has been noted that rapid movement displayed on the larger screens needed to fully appreciate the contents of the big pictures, requires higher frame rates to smoothly display movement. Thus BT.2020 includes frame rates extending up to 120 f/s. This presents considerable challenges for handling the resulting vast data.

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. Among the prominent projection technologies in the large projector area are D-ILA from JVC, SXRD from Sony and DLP from Texas Instruments. These projectors work by shining the projector light at reflective chips that display the image, so modulating the light that is reflected towards the projector’s lens. Movies are mostly made using 4K resolution, delivering great detail, without film’s scratches, dirt and weave, the audience is treated to consistent high quality results. Many digital cinema players and projectors can deliver 3D.

There is a wide range of digital projectors now available that are used for business presentations as well as for home cinema.

See also: Color management, Digital Cinema, DLP, D-ILA, SXRD

ProRes

A range of lossy, video compression systems developed by Apple Inc. Designed for editing it is described as ‘intermediate’, between uncompressed and more highly compress delivery quality. ProRes 422 can work with formats from SD to 5K using 10-bit, I-frame only, variable bit rate coding. For HD 60i there are three qualities; Normal 147 Mb/s, High-Quality 220 Mb/s and ProRes (LT) 100Mbit/s. There is also ProRes Proxy at 36 Mb/s for offline. For SD there are Normal 42 Mb/s and High-Quality 63 Mbit/s.

ProRes 4444 adds support for a 16-bit alpha (key) channel, and video sampling up to 12-bit.

See also: Quick Time

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.

pSF

A Progressive Segmented Frame (pSF) format splits a progressive image into two sequential fields. It is identical to 2:2 in terms of motion profile.

Purpose-built hardware

Hardware and software built for a specific task (e.g. a DVE), not general purpose (computer). Purpose-built hardware was 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. This became important in image processing where tasks require a great deal of power, especially as the demands increase in proportion to the picture area – significant for working with HDTV and UHD.

However, as standard/general-purpose platforms continue to become ever more powerful, so it can make sense to swap out some purpose-built hardware, which tends to be more costly, for software solutions. This ability to swap is a part of Quantel’s generationQ to use GPUs to provide accelerated image processing.