Television and Video Glossary -- P-R
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p (as in 60p) -- Frames per second for non-interlaced video.
P-Frame -- In a video compression scheme, data representing the differences between the complete subject frame and its predecessor. This is the most compact amount of data needed to generate the subject frame given the complete frame preceding, but it does not allow backwards single step or playback. See, also, I-Frame.
P&S -- Pan and Scan, q.v..
PAL -- Phase Alternate Line -- A 625 line 50 interlaced fields per second analog broadcast standard used in many parts of the world, primarily Europe, but not the U.S.A. So named because the chroma subsignal phase is different on each successive scan line to reduce picture artifacts. (NTSC uses such changing phase relationships also.) Programs are not interchangeable with NTSC even though they may occupy the same broadcast channels or be recorded on videocassettes of the same size and shape. Programs can be played back on SECAM equipment where they come out as black and white. There exist VCRs and TV sets that will play all three formats but they are not common in the U.S.A.
Pan and Scan -- Term used to describe a wide screen movie committed to video with a lesser aspect ratio. The picture is zoomed in on so that more or all of the TV screen is filled (to satisfy popular demand and improve vertical resolution), but both sides of the original picture obviously don't fit. A video technician "pans" the conversion machine (e.g. telecine) back and forth to capture what he considers or what he was told is the most important part of each scene while cropping the sides. Even film to film copies, notably 16mm and 8mm prints, have been made using the pan and scan technique. When you see the notice "... formatted to fit this screen ..." at the start of a movie broadcast on TV, that refers to the pan and scan transfer. In addition to losing "space" as the sides of the picture are cropped, movies as broadcast often lose "time" as they are "edited for (removal of possibly objectionable) content and to run in the time allotted".
Panamorph -- Trademark for an anamorphic lens that can be attached to many home theater or data grade video projectors to convert a 4:3 image to 16:9 or a 16:9 image to 2.35:1. The lens is advantageous when the best quality of image is achieved using the native lesser aspect ratio of the projector.
Passive Crossover, Filter, Switcher, etc. -- Refers to a circuit or group of electronic components that do not require any power other than the energy present in the input signal to perform the desired function.
Passive Radiator -- A woofer speaker cone that has no voice coil and whose vibration is caused by sound waves produced by another speaker in the same cabinet. It allows for some reinforcement of bass from the sound waves generated behind the powered speaker and also maintains the sealed cabinet needed for proper performance of acoustic suspension speakers.
Pay Per View -- Service offered by some cable TV or other program providers allowing a viewer to order a program by telephone (or nowadays sometimes directly through the cable TV tuner) and the system "unlocks" the tuner to permit viewing of the program. Generally applies to programs with predetermined fixed broadcast times. Programs that are broadcast only when someone orders them are referred to as "video on demand".
Pb, Pr -- Refer to the two color component video signals that accompany luminance (Y) to make up analog component video. Specifically, Pb = 0.564 ( B-Y ) and Pr = 0.713 ( R-Y). The normalizing factors were chosen so that the signals have a maximum of 0.500 volts and a minimum of -0.500 volts while Y varies from 0 to 1.000 volts not counting the negative going sync pulses.
Peak Music (or Momentary) Power Output (PMPO) -- Primarily an advertising gimmick. A measure of audio amplifier power output whose justification is that real life audio and music contains isolated short term peaks and can be faithfully reproduced by an amplifier that otherwise could not reproduce a continuous sine wave with such peak to peak voltages. There is no mathematical formula that relates a given stated PMPO with continuous sine wave output. Different equipment manufacturers compute PMPO using different methods that are often intended to yield the largest figure in watts for which measurements can prove. Amplifier power supplies contain capacitors that hold a charge that can act as a power reserve, and output sustained for but a a few milliseconds can sometimes be on the order of ten times the sustainable continuous power output.
Peek-A-Boo Scan Lines -- On what should be a non-interlaced display, usually an LCD panel, receiving a non-interlaced video signal, what appears to be every other row of pixels dark producing "gaps between scan lines" suggestive of interlaced video displayed on a CRT. It is more noticeable with eye movement following moving subjects. We believe it is intentional processing that darkens alternating rows of pixels on alternate approximately 1/60th second intervals to prevent comet trails and/or uses temporal dithering to achieve certain intensity (gray scale) steps.
Persistence -- Measure of how long phosphors (such as in a CRT) continue to emit light after excitation (such as from an electron beam) ceases. Long erpersistence reduces the visibility of gaps between the odd scan lines as the even scan lines fade etc. but increases motion blur.
Perverse Telecine -- Situation in 2-2 pulldown (such as for film to PAL video conversion) where pairs of (interlaced) video fields are arbitrarily treated as complete video frames and where each such "frame" contains content-wise non-matching odd and even fields.
Phone Plug/Jack -- A plug (and matching jack) 1/4 inch in diameter, the plug is just over an inch long. Originally used in telephone switchboards, it is still used for audio applications. A single plug can be used for two channels (e.g. stereo) when it has a third contact (the ring) between the usual tip contact and the rest of the plug further back (the sleeve). Similar plugs (and jacks) also come in a 1/8 inch or 3.5 mm diameter (Mini) size for mono or stereo and a 3/32" or 2.5 mm diameter (Micro) for mono only.
Phono Plug/Jack -- An RCA plug/jack. Originally used with record players.
Picture Height, as in "lines per picture height" -- Reference distance measurement for resolution of TV screens, used for horizontal as well as vertical discussion. So chosen because much of the time the resolution of a particular TV and video system was the same for a variety of screen sizes. Also chosen because resolution was traditionally measured across the largest circle that fits in the area referred to and for a TV screen the diameter of such a circle equals "one picture height".
Picture In a Picture -- A feature on TV sets whereby a small picture for a second program can be displayed in or near one corner of the screen. The viewer can switch back and forth as to which program occupies the whole screen. In order for two broadcasts to be so seen simultaneously the TV set must have two tuners (channel selectors). More commonly there is only one tuner and the second program must come from a VCR or other local source. Also, Picture Outside Picture for the second picture being outside the boundaries of the first picture which does not fill the screen.
Pillarbox -- Video formatting, typically for pictures of a lesser aspect ratio than the screen shape, where the picture fills the height of the screen and unused screen area is at the sides. Also (rarely) used to ensure that material at the extreme sides is not cropped due to overscan. See, also, Letterbox, Windowbox.
Pinna -- What we refer to as (or the exposed part of) a person's (or animal's) ear. It helps gather more sound waves than would otherwise reach a person's eardrums and also has directional characteristics so the person can better tell what direction a sound is coming from.
PIP -- Picture in a Picture
Pits and Lands -- An actual description of how data is encoded on an optical disk such as a CD or DVD. The reflective layer is smooth and flat except where pits or holes all in a continuous spiral and representing one continuous stream of digital data have been pressed or burned into the reflective layer.
Pixel, or Pel -- Picture element; the smallest spot on the screen that can be resolved as having a different brightness or color from what is next to it. The "number of pixels vertically" is equal to the number of scan lines; for example if you block off all but a narrow vertical stripe on the screen, you will see a series of dots, one per scan line. For a computer screen or digital video, the screen is divided into several hundred "grid positions" horizontally as well; a pixel must be exactly one of the grid positions, not half of one and half of the next. For analog TV pictures, we can say that the number of pixels horizontally is equal to the maximum number of alternating black and white dots that can be reproduced all the way across the screen, which equals the aspect ratio times the number of "lines of resolution per picture height" horizontally.
Pixellation -- A checkerboard or quilt like coarse grainy effect of tiny or even medium sized squares over portions of a picture. It is used to disguise or censor part of the picture content or is encountered due to inability of the processing of digital video to keep up with subject motion and other frame to frame changes.
Plasma Display -- Directly viewed digital video display consisting of a transparent panel as the viewing screen with an array of fine juxtaposed gas filled phosphor lined tubes or troughs or cells or pits, This is sandwiched by arrays of fine juxtaposed vertical conductive paths in front and horizontal conductive paths behind. To form a video picture, the conductive paths are energized in order one horizontal and one vertical at a time and the gas in the tube or cell where the paths cross is excited to give off ultraviolet light and the phosphors then glow, forming illuminated pixels. So named because the gas, when excited by electrical fields from the horiozontal and vertical conductors, enters a physical state referred to as plasma. The phosphors are the same kind sused on CRT tube viewing screens.
PMPO -- Peak Music Power Output; Peak Momentary Power Output, q.v.
Posterization -- Visible steps , bands, or stripes of slightly different shades of color (or gray), or a contour map effect, in what should be a smooth gradation of color shading (or gray shading) or blending. Results from the inability of the system to represent a large number of different shades of each color. Given two juxtaposed and different color patches as close to each other in terms of coloration as the system can render, the boundary between the patches is sometimes noticeable..
Pot -- Potentiometer, a kind of variable resistor, namely one with a fixed resistance element and with a sliding "center" tap. Usually found behind volume and tone control knobs and graphic equalizer sliders, also commonly used as the screwdriver adjustments in back of a TV set to fine tune convergence, pincushion distortion, etc.
Power Bandwidth -- The frequency range over which an amplifier can deliver at least half (within 3 dB of) its rated output in watts. This is not the same as frequency response which describes uniformity of output at lesser power levels with respect to input, over a frequency range.
PPV -- Pay Per View.
PQ -- Picture Quality.
Preamplifier -- (1) Amplifier stage used to bring a minute signal such as from a magnetic phonograph cartridge or a microphone to the usual line level (typically about one volt) so the signal can be treated similarly to other signals being switched and fed into a main amplifier. Such a "preamp" can be a stand alone component or can be combined with a main amplifier or power amplifier. (2) An audio component with switching circuits for audio and/or video sources and likely to contain but may not necessarily contain a phonograph preamplifier and/or surround sound processing circuits and/or optical audio input processing and/or radio broadcast tuners. Not contained are amplifier stages which drive loudspeakers.
Pre-Pro -- Short for "pre-amplifier processor" which in turn is another term for a pre-amplifier that includes features such as audio/video switching and/or video conversion (composite to S-video, etc.).
Presence Control -- Control in a three way speaker system that varies the signal level applied to the mid-range speaker. (The woofer level is seldom controlled.)
Presets -- Means for programming a tuner to allow quick "one button" selection of specific desired stations (as frequencies or channels). This can be implemented mechanically using cams and levers, or electronically using memory and computer circuits.
Prime, as in Y', R', etc. -- The video signal or its components are correctly referred to by the various terms Y, R-Y, G, Cb, etc. without the apostrophe or "prime symbol" when the signal has not been modified to compensate for the gamma of the picture tube or video display. The prime symbol is added, as in Y', Cb', etc. to refer to a video signal after gamma compensation. Prime Disclaimer -- To simplify things, all of the descriptions on this web site ignore the gamma compensation unless specifically discussing gamma, and the terms Y, R-Y, etc. are used without the apostrophe throughout. This represents a slight dumbing down and departure from correctness of the material on this web site.
psf -- Segmented Frame, q.v. Unfortunately often confused with "fps" for simply "frames per second"
Pulldown -- (1) The general term used to describe committing motion picture film material to video. So named because a projector or telecine machine typically has a "pulldown claw" to advance the film one frame at a time past the gate, or window through which the light beam from the projector lamp or other light source passes. The most common pulldown procedure is called 3-2 (or 2-3) pulldown (q.v.) since for immediate broadcast, alternating film frames are scanned three times and twice respectively before the pulldown claw is activated. (2) The slight slowing of a motion picture, video, or audio program for synchronizing purposes, or to cause it to run in the time allotted without editing of material. Pullup -- The slight speeding up of a motion picture, etc. for the purpose immediately preceding.
Push Pull Woofer System -- Speaker system with two woofers or subwoofers, one mounted normally, the other facing into the cabinet. The speakers are wired so both cones move "into" the cabinet at the same time, or in opposite directions relative to their respective frames and magnets. This configuration causes some even harmonic distortion caused by the speakers to cancel out.
PVR -- Personal Video Recorder; a digital video recorder.
Q (Quadrature Color Component)-- Video subsignal representing yellowish green to purple color content, used in NTSC broadcasting. See I, Q.
QAM -- Quadrature (Amplitude) Modulation .
QLED -- Quantum dot light emitting diode--- Refers to direct view TV sets and video displays similar to LED TVs with the stencil of LCD pixels in front of a back light panel with LEDs to form the image. Instead of or in addition to a screen layer with red, green, and blue passive subpixel filtering elements, there is a layer with quantom dots (q.v.) to enhance the color including providing increased brightness and color intensity. QLED was originally Samsung's trademark but has been made available to other manufacturers of TV/video screens with quantom dot technology.
QNED -- Quantum Nanocell Light Emitting Diode -- LG Electronics's TV/video display screen technology using its proprietary nanocell molecular layer to absorb, say, traces of blue from the red subpixels ,and thus enhance and purify colors. The display screen starts with the LED illuminated back light panel and LCD pixel stencil in front of it to form the image, lujminance wise. Then the light (from the red, green, and blue subpixel positions) goes through a quantum dot layer to convert more of the (white) light content to the red, green, and blue for the respective subpixels, and then through the nanocell layer to purify the respective subpixel contents. LG Electronics was denied a trademark for "QNED."
Quadrature Modulation -- A form of amplitude modulation where two signals can be modulated on the same carrier producing a single modulated signal with differing sidebands. The encoding of the two original signals involves phase relationships. It is not true that one signal is represented by the lower sideband and the other by the upper sideband, but both sidebands are needed to recover the original signals. A very common use is combining the two color components (Pb, Pr) of analog component video into a single color signal which in turn may be combined with luminance to form a single analog signal (composite video) that carries all of the essential video information. In video color practice a considerable amount of the higher frequency content and therefore horizontal resolution of the color components is lost so that the overall signal can be constrained to a certain bandwidth.
Quantum Dots -- Special materials or chemicals which emit light of one color when excited by light of a different color. The effect is comparable to phosphors excited by an electron beam or ultraviolet light. For example the blue component of white light might be converted to red so more of the total (white) backlight energy gotes through a red subpixel filter and less light output is wasted by being absorbed by said color filter. Better, more intense, and more accurate color reproduction is obtained compared with using only (passive) red, green, and blue filters.
q.v. -- (quid videt; "which see") -- Means to go to or look up the description of the item immediately preceding. On this web site, sometimes we provide a link so if you click on the "q.v." the respective page or paragraph appears.
R-Y (approximately Pr for analog video or Cr for digital video or V for some applications including PAL)-- Video signal component consisting of the picture red content from which has been subtracted the overall luminance (Y). See B-Y and also see Prime Disclaimer.
Radio Frequency -- For video, refers to the antenna inputs to a TV set, or the overall video signal containing many channels modulated on carrier frequencies as input to the TV set's tuner. Also refers to audio channels encoded on video disks by being modulated onto carrier frequencies as if they were going to be broadcast.
Radio Frequency Interference -- (1) Interference to radio and TV programs imparted when the programs are still modulated on carrier waves, during broadcast or during transmission via a cable system. (2) Electromagnetic energy capable of causing interference to radio and TV programs being broadcast.
Rainbow Effects -- Red, green, or blue edges on moving subject matter caused by the sequential projection of red, green, and blue picture content from a video projector with a single image generating element and a color wheel, which projectors include all modestly priced DLP projectors. Although the better color wheel projectors produce sets of red, green, and blue sub-images that match in content and also more flashes per second, the viewer's eye movements may still result in the viewer's seeing the colored edges.
Rainbow Swirls -- See Cross Color.
RAM -- Random Access Memory.
Random Access Memory -- The memory chips in a computer (or memory cores in very old computers). More generally, data storage where desired material or empty storage space can be located computationally or by lookup, and then accessed directly, specifically without having to riffle through intervening material and without having to take hints from indexing along the way. By contrast, tape is a sequential access medium as opposed to a random access medium.
Raster -- The illuminated rectangle on the face of a picture tube (CRT) produced by the scan lines whether showing a picture, a solid color, or snow (noise). "Underscan is when the raster does not fill the screen."
RBE -- Rainbow Effects, q.v..
RCA Plug and Jack -- A press-fit plug and jack connector with one conductor plus ground introduced (in the 1930s?) by Radio Corporation of America, later part of Thomson Electronics. The jack is a metal stud a little larger around than a pencil (about 3/8 inch) with a center hole that a small lollipop stick would fit (about 1/8 inch). The matching plug has one fat (1/8 inch) center pin that represents the live conductor, and a shell that presses onto the jack stud and that is almost always grounded. Normally the center pin is connected to the center conductor of a coaxial cable and the shell is connected to the shell or shield of the cable.
Reactance -- Resistance to the flow of alternating current within imposed by a coil of wire together with any metal about it, over and above the resistance to direct current the same coil of wire assembly imposes.The greater the frequency of the alternating current, or audio/video signal, the greater the reactance of a given coil.
Read Only Memory -- Data storage that may not be altered or modified during normal or routine use
Real Time Counter -- A display of elapsed hours, minutes, and seconds on a disk player or tape player, the information derived from video frames or from timing data encoded on a tape, contrasted with a counter that registers according to revolutions of a reel or spool or according to some other arbitrary method.
Rear Projection TV (set) -- A TV set in a "boxy" cabinet and having an optical system consisting of (for color TV, usually three) small CRTs or LCD panels or other picture forming elements, together with lenses and mirrors and perhaps a projection lamp used to project a picture against the back side of a translucent panel that serves as the viewing screen. RPTVs typically have screens ranging from 35 to 70 inches in size. The same concept is also used for small film and viewgraph viewers.
Receiver -- The best short definition of this term as it applies to electronics is "a device that captures an over the air broadcast (or satellite or cable or microwave transmission) and presents it for listening, data processing, or viewing". A "television receiver" is the complete TV set as we know it, which includes the cabinet, picture tube, loudspeaker, channel selector, usually a built in antenna, and all the related electronics. A "radio receiver" f.k.a. "radiotelephone receiver" is a "radio" as we know it, with built in antenna, tuning dial, loudspeaker, volume control, etc. But a "stereo receiver" generally does not include the antenna or loudspeakers, although it refers to the unit with everything else needed to receive FM stereo broadcasts, namely the case with built in radio tuner and tuning dial, amplifiers, volume and tone controls, sometimes pre-amplifiers for phonographs, etc. And an "audio visual receiver" generally includes a radio broadcast tuner, switching for video sources, audio amplifiers, but not a television broadcast tuner.
Red Push -- Accentuation of reds for the purpose of making flesh tones more attractive although not necessarily more correct. It is usually accomplished by designing of the color decoder to not conform strictly with the video standards and as a result it usually cannot be eliminated.
Regional Code-- Coding on a DVD intended to restrict playing of the DVD and therefore restrict release of the program content to specific geographic regions around the world. Roughly, Region 1 is the U.S.A. and Canada, Region 2 is most of Europe, Region 3 is most of Asia except China, Region 4 is the Australian continent, Mexico and South America, Region 5 is Russia, most of Africa, and India, and Region 6 is mainland China. A region code of zero means no restrictions.
Registration -- Convergence of the sub-images in each of the primary colors as it applies on the screen with respect to the three CRTs or LCD panels of a projection TV set, or on the printed page with respect to plates on printing presses, as opposed to with respect to electron beams that paint one spot at a time on a direct view CRT.
Repeater -- An amplifier (together with receiving and transmitting antennas if the signal is transmitted through the air) not at the beginning or end of a long transmission path and used to boost the strength of signals transmitted along/over that path. Applications could include the distribution of video within a building.
Resampling -- In video, the conversion of a video frame to have a different number of scan lines or pixels but also using artificial intelligence to make the picture look as if it originally had the final number of scan line or pixels. Specifically, various blending techniques involving almost all of the picture content are used so the finished frame does not look as if individual scan lines or rows of pixels or columns of pixels here and there were simply dropped or duplicated. Still, picture quality is lost irreversibly whenever resampling is done to yield a set of pixels less than twice the original set both horizontally and vertically. Significant picture quality loss occurs when resampling is done to yield a set of pixels less than about 140% (or reciprocal of the Kell factor) of the original set in each direction. This is because the only way to figure out what each new pixel should be is to interpolate (guess based on the nearest old pixels).
Resolution -- (1) Ability of a system to represent detail, expressed as pixels, lines or line pairs over some distance such as inches. For visual media, lines of resolution or line pairs of resolution is traditionally measured across the largest (perfect) circle that fits in the area being referred to. For a standard TV screen, such a circle would span 3/4 of the screen width. A lot of advertising deception involves mis-stating the lines of resolution to span the entire screen width. The number of lines of resolution horizontally need not equal the number of lines of resolution vertically (or diagonally). Because pixels can straddle and thereby lose detail in a digital system but not in an analog system, the number of pixels does not equal the number of lines of resolution (see Kell Factor). If resolution is expressed in pixels, both the horizontal pixel count and vertical pixel count spanning the entire screen should be specified. (2) Any one of a collection of formats for digital video in the sense that each "resolution" consists of a given number of pixels expressed as so many pixels horizontal by so many pixels vertically such as 640 x 480, together with other parameter specifications such as so many frames per second and/or so many microseconds for a horizontal retrace interval. So named because such a format can represent visual material with that many lines of resolution under ideal circumstances. Click here for more discussion on resolution.
Resolution Pumping -- The entire picture becomes slightly less sharp (typically when something starts moving) and sharpens up again a little later (typically when the scene becomes still). A common cause is less than sophisticated conversion from interlaced to progressive scanning (de-interlacing)..
RF -- Radio Frequency(ies). RFI -- Radio Frequency Interference.
RGB -- An analog video signal transmitted as three components (subsignals) using three wires and which subsignals are the respective picture color content of red, green, and blue, respectively. R, G, B -- The red, green, and blue components referred to separately. RGBHV -- The RGB signal where horizontal and vertical synchronization (sub)signals are carried on fourth and fifth wires, respectively. RGBS -- The RGB signal where horizontal and vertical sync. are combined (composite sync.) and carried on a fourth wire. RGsB -- The RGB signal with sync. combined with the green signal so that just three wires are needed. (There are no official designations for sync. on blue or sync. on red although these subsignals occasionally have sync. included as well.). RGBcvbS -- The RGB signal with sync. provided by an accompanying composite video signal with the same scan and frame rate on a fourth wire, often encountered with equipment using SCART jacks. Not all equipment that accepts RGBS will work with RGBcvbS although external devices exist that will strip off the (positive going) composite video from the (negative going) sync. pulses. (2) RGB by itself may be used to refer to red, green, and blue together in any context.
RGB-OLED --A more descriptive term for the original organic light emitting diode video screen/display technology, with just red, green, and blue (no white or other) subpixels at each pixel position.
RGBW -- Digital video/TV screen technology with white and colored subpixels but not all of red, green, and blue present at every pixel position. Common layouts are alternating pixels with red, green, and blue subpixels and with single white LEDs, and alternating pixels with red and green subpixels and with blue and white subpixels. This writer regards RGBW as capable of full luminance resolution, and that the degradation of color resolution especially on 1080i HDTV and higher resolution screens is not very obtrusive to the human eye. See, also, WRGB.
RIAA -- Recording Industry Association of America, a group that develops standards and policies for recordings. RIAA Curve -- A standardized frequency response curve (or contour) for recording of phonograph records, notably with attenuation of bass frequencies during recording to reduce the excursion of the cutting stylus, permit closer spacing of record grooves, and increase possible recording time, together with a compensating contour with bass boost for use at playback time.
Ringing -- In video, closely spaced repeated ghosts of a vertical or diagonal edge where dark changes to light or vice versa, going from left to right. The electron beam upon changing from dark to light or vice versa instead of changing quickly to the desired intensity and staying there, overshoots and undershoots a few times. This bouncing could occur anywhere in the electronics or cabling and is often caused by or accentuated by a too high setting of the sharpness control.
RMS -- Root Mean Square, q.v.
ROM -- Read Only Memory.
Root Mean Square -- The peak to peak voltage value of alternating current that is a square wave and that is otherwise equivalent to AC of said voltage that is a sine wave. The value is 0.707 times the sine wave peak to peak value. For amplifier power measurements, RMS is used to describe power output when the signal is a continuous sine wave.
RPTV -- Rear Projection Television (set)
Rumble -- Low frequency mechanical noise or vibration (such as from a motor) picked up by a phonograph needle and cartridge assembly and amplified, or picked up by a phonograph record cutting stylus assembly and recorded on the disk along with the audio.
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