Television and Video Glossary -- H-L
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Hard Matte -- Refers to wide screen movies that are filmed using a camera that blocks off the top and bottom edges of the 4:3 aspect ratio film frame, recording only that part of the image that will become the finished picture and leaving unused the top and bottom edges of each frame on the film. (This is how panoramic 35mm still cameras work.) Some producers use this technique so that the theater projectionist cannot err (or deliberately modify the presentation) by opening up the projector's aperture plates too much.
Harmonic Distortion -- Distortion in audio consisting of the addition of multiples (harmonics aka overtones) of the frequencies originally present in the source material. Harmonic distortion in an amplifier occurs when the relationship between the input voltage and the output voltage (the transfer characteristic) is not uniform (linear).
HDCP (High-bandwidth Digital Content Protection) -- A data encrypting system developed by Intel, Inc. to inhibit the unauthorized distribution of digital video material through copying. It consists of "keys" (data) incorporated in the video data together with proprietary encryption (scrambling) circuitry and software in the various video components (tuner, TV, DVD player, etc.) that handle HDTV. Material that is protected may only be transmitted digitally and to components that decrypt the material prior to processing and re-encrypt the material before transmitting the material to another component using certain digital transmission formats including DVI that include the encryption.
HD-DVD -- Trademark for a now obsolete format for a DVD used for high definition video. The format was conceived in 2002 with Toshiba and NEC as the initial developers. The first players and disks were marketed in 2006. In 2008, support and interest declined in favor of the Blu-Ray format, and HD-DVD faded away.
HDMI (High Definition Multimedia Interface)-- A set of digital video standards for transmitting video and audio together and also component remote control signals over wires between components such as between DVD player and TV set at distances up to about 30 feet. The video data formats are the same as for DVI, including for ATSC HDTV transmission, but not all of the TV video formats and none of the "personal computer" video formats are included in the standard. The plug or jack assembly is rectangular-ish about 3/4 inch by 3/8 inch.
HDR (High Dynamic Range) -- In digital video, using ten bits instead of eight for each pixel's luminance or for color information, allowing approximately 1000 gradations instead of approximately 250. This has been used to provide added picture detail in highlights and shadows without having visible steps or "contour lines" (posterization) in what should be areas or color patches with gradual continuous change in shading..
HDTV -- High Definition Television.
HD Built-In -- Refers to a (full fledged) HDTV receiver, that is, a TV set with HDTV tuner, and with video circuits,and display elements to display all standard HDTV programs using at least one of the HDTV formats. Current marketing standards do not disqualify a set from having the HD Built-In label due to deficiencies in de-interlacing, video bandwidth, or optical resolution.
HD Capable -- HD Built-In.
HD Ready -- Refers to a TV set that accepts baseband video in one or more of the high definition formats, that displays a picture using one or more of the high definition video formats, but which does not have a tuner (channel selector) to receive HDTV signals off the air or from a cable system.
Head End -- The equipment that formats and combines and modulates the various audio and video source materials to occupy the channels of a cable or satellite TV system, or the physical location of said equipment.
High Definition Television -- A generic term describing TV signals, video formats, and equipment, providing either (1) pictures of approximately twice the horizontal resolution and twice the vertical resolution of common standard late 20'th century TV broadcasts extrapolated to a 16:9 aspect ratio, or (2) pictures made up of approximately a million pixels or more. 1280 x 720, or 0.92 megapixel, is generally regarded as the lower limit of picture detail content or resolution for HDTV. See, also, ATSC.
Home Run -- Continuous cable that runs from a room outlet box to an electric panel or other large central junction box as opposed to daisy chaining from one outlet box to another. For audio and video cables, this is recommended over cable runs from one room to another room where the permutations become too numerous and complicated. Also the use of branching, splicing, and splitters in audio and video cable runs in the walls is very undesirable. Individual cables are much preferred.
Home Theater -- (1) Place in the home where movies, skits, puppet shows, etc. may be presented and which is customarily used for those purposes, usually where the seats, fixtures and equipment are left in place when not in use. (2) The concept and art of presenting movies in the home with most of the ambience of a well run commercial movie theater, which includes showing the movie in its original aspect ratio and not edited or formatted for TV, and providing left, right, and rear sound channels. In the early days of home theater, one minimum standard called for a screen of only 27 inches from corner to corner although accompanied by at least five sound channels for movies.
Home Theater In A Box -- A (usually modestly priced) kit consisting of a DVD player, A/V receiver with several audio amplifier channels, cables, and several speakers usually including a subwoofer (but no TV or video monitor). So called because the kit is usually packaged in one, or nowadays usually two, cardboard box(es).Usually does not have enough amplifier power to produce sound levels comparable to a commercial theater in a large room.
Home Theater Personal Computer -- A computer used to process video in the home and equipped with specialized software, video cards and other equipment for that purpose.
Horizontal Retrace Interval; Horizontal Blanking Interval -- The time during which the electron beam is turned almost off (as if to draw black) and moved from right to left to get ready to draw the next scan line on the picture tube. Roughly, the horizontal retrace interval starts with a few milliseconds of zero level (the front porch) followed by a few milliseconds of negative signal level (the sync. pulse) followed by a few milliseconds of zero level (the back porch). In NTSC broadcast video, 10.9 microseconds are set aside for this purpose; the entire scan line, retrace interval and all, takes 63.5 microseconds. The time it takes to draw an entire line is adequate to allow the electron beam to draw at most 530 dots alternating black and white, given a 4.2 MHz bandwidth; the horizontal retrace interval takes away about 90 of these dots. Of the remaining 440 (give or take a few), 330 fit in the largest circle that in turn fits in the 4:3 screen, which leads to the 330 line horizontal resolution that is often mentioned when it comes to NTSC analog broadcast TV. The smallest dot achievable which determines the maximum number of dots into which a scan line may be subdivided also depends on the program source and the quality of equipment. The term also refers to additional data separating the data representing each row of pixels in digital video.
Hot Spotting -- Some parts of the picture, always the same parts of the screen for a given seating position, are brighter than other parts. This happens when the screen, usually by design, reflects more of the projected light in some directions than in other directions, hopefully more towards the favored seating positions. Except that the light projected towards the left side of the screen may reflect differently compared with light projected towards the right side.
HTiB -- Home Theater in a Box, q.v..
HTPC -- Home Theater Personal Computer, q.v..
Hue -- A "single color" disregarding lightness or darkness (luminance). A simple somewhat vague way to describe hue is to say that pink and red are of the same hue and azure, blue, and navy are of the same hue. Hue Control -- Another name for Tint Control.
Hulu -- A subscription service offering a large library of films and TV shows plus live TV and news as video-on-demand, usinsgstreaming via the internet. Owned by Disney (majority ownership) and Comcast. Some of the offerings are not exclusive i.e. are.also available on competing streaming services.
i (as in 50i, 60i, etc.) -- Fields per second, or a letter code to refer to interlaced video as opposed to progressive scan video. Much literature nowadays is describing interlaced video using written formats such as 480/60i, namely. with the "i" after the field rate.
I (In Phase Color Component) -- Video subsignal representing reddish orange to greenish blue color content, used for NTSC broadcasting. The term is not quite correct since the I component is actually about 33 degrees out of phase while in-phase demodulation of the color subcarrier yields the B-Y or Pb component. See I, Q.
I-Frame (Intra-Frame) -- In a video compression scheme, such as for picture information on a DVD, a frame that is complete. In order to begin playback, an I-frame must be located. Other frames (B-frames, P-frames, q.v.) are just the differences from adjacent frames. Thus frame 1 may be an I-frame. Frame 2 on the DVD might be a P-frame which when combined with frame 1, yields the complete frame 2 for display. Frame 3 on the DVD might be a B-frame which when combined with the complete frame 2 we just derived (or from complete frame 4 in backwards single stepping), yields the complete Frame 3, and so on. Usually there is an I-frame about every ten frames, so the player doesn't have to hunt too far when resuming playback after a manual pause in the middle of the program.
IEEE (Institute of Electrical and Electronics Engineers) -- A professional organization which has established some standards for radio and television electronics. Formerly Institute of Radio Engineers (IRE).
IM -- Intermodulation, usually used to describe distortion, as in IM distortion.
Image Stabilization -- Means of reducing shakiness in motion pictures (or blur in still pictures) recorded by hand held cameras. A typical optical method uses gyroscopes, which inhibit sudden or rapid rotational twisting or panning movements. Some newer methods for still cameras use moving lens elements. Electronic methods for video cameras attempt to shift field or frame subject content horizontally or vertically by a few pixels so as to match the content of a previous field or frame. Electronic image stabilization of interlaced video often results in reduced vertical resolution.
Integrated Amplifier -- Another term for an audio amplifier unit with preamplifier stages for microphones and/or phonograph cartridges, switching of multiple inputs, tone controls, and power amplifier stages to drive speakers.
Interlaced -- The drawing or transmission of all of the odd scan lines, then all of the even lines, for each video frame. Interlaced video was originally invented to reduce flicker given that the video technology of the time could not draw video frames fast enough to keep the top of the picture from fading on a CRT before the bottom of the picture was completed.
Interlace Factor -- The ratio of the number of psychologically perceived analog lines of vertical resolution in an interlaced video picture to that in a progressively scanned video picture, both pictures having the same number of scan lines and both pictures otherwise being equivalent. It is difficult to evaluate the interlace factor because it is difficult to produce interlaced and progressively scanned pictures with all other characteristics equal. See, also, Kell Factor.
Intermodulation Distortion -- Distortion, such as generated in an audio amplifier, consisting of spurious frequences that are sums or differences of frequencies in the original source material, as if amplitude modulation was taking place.
Interpolation -- Guessing what goes in between. A typical example in video is converting the video to have a different number of scan lines or pixels. If we imagine both a grid of the source pixels and a grid of the target pixels on the screen at the same time, a target pixel may be centered between two (or among four) source pixels. Sophisticated interpolation is not just taking the average of the nearest source pixels' content but may also vary from pixel to pixel and even be influenced by the content of pixels several removed from each target pixel. (Guessing what comes next or what goes beyond is called extrapolation.)
Invar -- Trademark for a metal alloy used for picture tube shadow masks, which alloy expands and contracts due to temperature changes less than most metals. Used so that more brightness can be obtained which requires stronger electron beams which in turn cause the shadow mask to heat up more and where expansion causes the holes to go out of alignment with the phosphor dots or stripes, in turn causing picture discoloration.
IPG -- Interactive Program Guide. See Electronic Program Guide.
I-Q -- Refers to one method of encoding of the color content of a video signal such that all colors could be depicted using a two dimensional diagram, more specifically a color wheel. There are two color signals one (I or In Phase) of which represents oranges and blues and the other (Q or Quadrature) represents greens and purples. (Both together are used to represent other colors.) This choice of colors permits giving the oranges and blues, which the human eye is more sensitive to, more frequency bandwidth (1.3 MHz standard) and thus greater color resolution in NTSC video. The remaining colors had to be limited to about 40 lines of resolution (0.5 MHz sideband width) since one of the sidebands of the modulated color signal is so limited and both the I and Q color components cannot be recovered from just the other sideband. Many TV sets today and all consumer VCRs limit color resolution to a theoretical maximum of 40 lines for all colors due to inexpensive circuitry. When it is not necessary to construct a composite video signal, the color signals U and V representing (approximately) blue-yellow and red-cyan respectively, are usually used instead of I and Q. We believe that all of the descriptions on this page can be understood quite well by persons without tremendously high intelligence quotients. Click here for more on video signal formats.
IR -- Infra-red. Most TV and similar remote controls use a modulated beam of infra red light.
IRE (Institute of Radio Engineers) -- Former name of the IEEE. The term IRE is still used with some electronic standards such as video signal brightness level e.g. 50 IRE.
iScan -- Trademark of Anchor Bay Technologies (company may have changed hands recently) for its line of stand alone de-interlacers and scalers, which are also usable as NTSC to VGA converters.
ISF -- Imaging Science Foundation, a group of professionals that sets standards for calibrating of television and video equipment.
JPEG -- Joint Photographic Experts Group -- Organization which, among other things, developed standards for digital compression of material representing pictures, photographs, and motion pictures.
Judder -- Minute unnatural jerky movements in motion pictures, either in space or in time. It (in space) can be the result of consecutive film frames not pulled precisely to the same position in the projector gate. In terms of time, judder in video may be noticed because 24 frames per second for film source does not divide evenly into 60 fields or frames per second for NTSC video, and some film frames' content is shown on the screen for more time than other frames' content (3-2 pulldown, sometimes becoming 4-2 pulldown in certain situations).
Jumbotron -- Trademark for a video display, typically several feet across, using clusters of discrete LEDs for its pixels. These LEDs being approximately 1/8 inch in diameter each, with red, green, and blue ones for each pixel, the resolution of the display is typically far below current HDTV resolutions.
Kell Factor -- The ratio of the number of psychologically perceived lines of resolution to the number of scan lines or pixels (spanning the same distance) taking into account all possible deficiences related to scan lines and pixels including gaps between the latter and including the fact that scan lines or pixels can straddle details in the original subject leading to in some cases a total blur, but not counting the effects of interlacing. The larger the better, 0.7 is considered very good. Deficiencies such as scan lines too thin or too thick, and flickering due to a low scan rate worsen the Kell factor. Click here for more on Kell factors. See, also, Interlace Factor.
Keystoning -- The trapezoidal or other departure from perfect rectangular shape of a projected picture because the projector from its sitting or hanging position has to be aimed at the screen at an angle that is not correct for it. The further from the lens the projector beam goes, the more stretched out will be the picture content at that place on the screen. Some video projectors have electronic keystone correction which electronically reshapes the picture on the display elements within to compensate for this projection distortion and cause the picture as projected on the screen to be in the proper shape. Some projectors have optical keystone correction achieved by adjusting lenses or mirrors inside.
Kinescope -- (originally a trademark) A CRT; picture tube, also a movie produced by capturing (cinematographing; filming) the picture as displayed on a TV screen. The word may have originated from the small portion of the field of vision spanned by the (at the time) small TV screen at normal viewing distance; being similar to the portion of the field of vision spanned by the image seen in a microscope or telescope.
Large -- Setting on an amplifier that does not restrict the bass frequencies to a separate subwoofer output channel. Used when there is no subwoofer and/or when the other speaker systems have their own woofers (and are probably physically large) and are not vulnerable to overdriving if fed the full frequency range audio.
Laser Disk -- The accepted terminology for now obsolete 12 inch consumer playback only video disks recorded and read using a laser (and also 8 inch disks recorded using the same format). The video recording is of a composite video analog signal with about 5.3 MHz of luminance bandwidth which gives a maximum horizontal resolution of 425 lines per 4:3 picture height. There are two analog soundtracks and two digital soundtracks; not all players can play the digital soundtracks. All players can play both the CAV and CLV disk formats.
Laser Rot -- Tarnishing of the (metallic) reflective layer in a laserdisk or DVD or similar disk, making the disk unplayable, unreadable by the player's laser. Caused by a defect in manufacturing or deterioration of various materials in the disk that results in moisture reaching the reflective layer.
Layer -- A DVD is constructed of several layers of different materials. There are up to four data containing layers and the player can play two of these layers in sequence without the disk's being removed and turned over. Each layer can hold approximately two hours of standard definition (e.g. NTSC; PAL) video. To play "the other layer" the player's laser beam is refocused slightly. Layer Change -- The jitter or stutter that sometimes occurs as the DVD player reaches the end of the recorded material on one layer and switches to playing the other layer.
LCD -- Liquid Crystal Display, q.v.
LCD TV -- Applies to TV sets and video screens/displays with liquid crystal display (q.v.) panel or panel layer with the array of rows and columns of pixels as a dynamic stencil to form the image in "black and white.", This is positioned in front of an illuminated screen sized panel (direct view sets) or in a light beam (projection sets), For color, another screen sized layer has an array of translucent almost microscopic red, green, and blue cellophane like filters as subpixels. For projection sets, usually there are three LCD stencils for red, green, and blue respectively, and the three light beams are superimposed on the screen. In 2023 the stencil of LCD pixels is still the predominant image producing element in TV and video screens and displays although fluorescent back ligthing has largely been superceded by LEDs. The LCD stencil in front of an opaque (usually) white panel has been used for signs and changeable graphics and "electronic books" but does not give TV quality pictures in terms of contrast and gray scale.
LCoS -- Liquid Crystal on Silicon.
LD -- Laser disk .LD also refers to that format that became marketed for home video with thousands of movie titles issued and developed jointly by MCA and Philips.
LED -- Light Emitting Diode -- An electronic component containing solid material that emits light when electricity passes through it, without the use of vacuum, gas, heating elements, supply of fresh material or fuel, or removal of spent material. .(Diode refers to the component's conducting electricity in one direction only; other components in the same circuit supplied with alternating current will receive a pulsating direct current.)
LED TV -- Currently refers to an LCD TV set (with back light panel, liquid crystal pixel stencil layer, and subpixel layer of red, green, blue filters) where light emitting diodes illuminate the back light panel. (or provide a projection light beam). Different names and terms, such as OLED and Jumbotron(tm), have been used to refer to sets with no back light and where pixels or colored subpixels are individual LEDs, or where color is derived other than by using an array of subpixel sized colored cellophanes..
Lens Shift -- Ability of a projector to optically shift the projected image up or down or from side to side relative to the projector to screen axis, that is, without repositioning or tilting of the projector, and also without electronic scaling, shrinking, or stretching of the image.
Letterbox -- The colloquial term used to describe a video program where the original scene has a larger (wider) aspect ratio than the TV screen and is zoomed out (shrunk) so that the entire width fits in the screen. An inescapable consequence is that there is unused screen area and wasted scan lines/pixel rows at the top and bottom. The term came about because viewers had the impression they were looking through a mail slot in a door or out of the slot of a gigantic mailbox. The vertical resolution of subject matter in letterbox editions is less compared with full screen pan and scan editions of movies. Although I have not seen any movies prepared for video in the following way it might have been interesting to gauge the public's reaction if instead of black bars, an image of a theater proscenium curtain appeared above and below the letterboxed picture.
LFE -- Low Frequency Effects.
Linear Audio Track, Linear Stereo Tracks -- The analog audio track(s) positioned at one edge of a video tape and recorded/played back by a separate stationary tape head. Due to the slow linear tape speed, the high frequency response of consumer VCR recording on these tracks is quite limited, extending to perhaps 8 KHz at most. Also, due to the precision of mechanical parts needed for accurate slow tape movement, wow and flutter is more likely to be greater.
Line Doubler (...Tripler, ...Quadrupler) -- A device whose purpose is to output video fields or frames with twice (or three times or four times) as many scan lines, which task is most simply accomplished by delivering each scan line's content to the the TV set twice (... three times, ... four times) and in quicker succession to keep up with the incoming field or frame rate. The original purpose of these devices was to reformat standard video for specialized video projectors and specialized large screen TV sets (then rarely seen outside professional environments) which use more scan lines to avoid showing noticeable gaps between scan lines. Today's de-interlacers are loosely also called line doublers because their output is video of the same format as that from a "plain" line doubler. High quality de-interlacers use techniques more complicated than just delivering each scan line twice. Click here for more detailed information.
Line Level -- The voltage level, usually around one volt, at which audio or video signals are transmitted from one component to another such as from a DVD player to a TV set, but not counting microphone connections (a much lower level) or speaker connections (a much higher level). Standards exist for the voltage levels so that most components from different manufacturers can be connected together easily, but occasionally a non-standard voltage level may be encountered for signal transmission between two specific components.
Line Pair -- On a test pattern consisting of closely spaced black parallel lines on a white background, a line pair is one black line together with the white space on one side of it. When photographers say "lines of resolution", they mean line pairs. In television and video, one line pair equals two TV lines, or two pixels, of resolution.
Line Pairing -- Superimposing of the respective scan lines of odd and even interlaced fields on the (CRT) screen, generally due to a defect or miscalibration of the TV set. The result is halving of the vertical resolution as well as (usually) more noticeable gaps between scan lines. The "540p mode" on a CRT HDTV set is nothing more than intentional line pairing of what would otherwise be a 1080i display.
Lip Sync. Error -- Situation in motion pictures where picture and sound are not synchronized in time. So named because the error is particularly noticeable as subject lip movement that does not match the words spoken. For film and some videotape methods, the sound head is several inches away from the projector gate / video heads, recording and production takes that into account, but careful adjustment is still needed. Video processing units, such as line doublers that accumulate several frames of video in order to do their processing, can introduce lip sync. error.
Liquid Cooled Tube -- A (vacuum) tube with a surrounding jacket or cavity filled with liquid for conducting away of heat. For CRT projection TV the cooling liquid is typically contained in the lens assembly mounted against the faceplate (display screen surface) of the tube where, incidentally, most of the heat is generated.
Liquid Crystal Display -- A panel on which tiny spots become transparent or almost opaque in response to electronic signals and which, given enough of such spots, can display changeable text, graphics, patterns, and images. For TV and video, an array of thousands or even millions of LCD elemenst as rows and columns of pixels is used as a dynamically changing stencil over an illuminated (usually) white screen sized panelor in a projector's light beam to display images and motion pictures. The opacity of spots (or pixels) on the stencil depends on polarization. The crystals themselves change polarization and they together with an additional covering panel or layer that imparts a fixed polarization combine effects to determine how much light is transmitted and therefore determine the brightness of each pixel. Liquid Crystal on Silicon -- A liquid crystal display panel or element, for projection TV, with the crystals atop a mirror rather than on a transparent panel. Its advantage over regular LCD is a higher contrast video image in that the light beam must pass through the liquid crystals stencil twice, (reflecting off the mirrored surface behind).
Lobing-- Fading due to cancellation of sound as one moves about the room when there are several speakers in use, including multiple speakers in the same cabinet. So named because a graph of sound intensity (loudness) versus angle off the speaker cluster center axis suggests multiple fingers or lobes or wings. The locations where cancellation is heard vary with the frequency being reproduced. Since sound bounces off the walls, it is almost impossible to predict where in a room the best sound quality will be heard.
Local Dimming -- In LED back lit TV and video screens, the ability to selectively dim individual or groups of LEDs to achieve deeper blacks in parts of the picture with predomiinantly dark content. This is done because the LCD pixel layer, or dynamic stencil, which governs luminance content, does not block all of the back light coming through the areas of the picture intended to be black. It is not perfect; what should be a large uniform black area, such as a star studded night sky, may have gray patches where the LEDs behind are brighter e.g. where stars are positioned.
Long Play -- The "middle" tape speed of a VHS VCR yielding four hours of recording/playback time on a "two hour T-120" tape. It was introduced shortly after VHS VCR's themselves were introduced (with a single faster speed). Not all VCR's will make recordings at the LP speed.
Lossy -- Refers to compression methods that discard some of the information or data to make a video or audio program occupy less storage space or less transmission bandwidth. This results in inability to perfectly reconstruct the original program. Lossless -- Refers to compression methods from which the exact original can be reconstructed.
Loudness Control -- Control on an audio amplifier that (switches in a circuit that) adds bass boost and some treble boost as the volume control is turned down, to counteract the human ear's lesser sensitivity to low and high frequencies at lower volumes.
Low Frequency Effects -- Bass, and the vibrations produced by bass shakers, if any.
Lower Field -- The field of "odd" scan lines is called the lower field because it usually possesses the lowermost scan line containing picture information. This scan line may contain only a half line's worth of picture information.
LP -- (1) Long Play, q.v.; "middle" tape speed on a VCR. (2) A 33-1/3 RPM phonograph record, long playing compared with the (1950's) previously standard 78 RPM records.
Luminance, or Luma -- Brightness of a light emitting object, or the portion of a video signal that represents brightness. Used by itself, the luminance signal is sufficient to produce a full black and white image. It is said that the luminance signal is responsible for the picture detail. This is true because as the video standards (NTSC, etc.) were defined, the luminance signal was given a larger bandwidth to permit the carrying of all of the picture detail while the color signal was deliberately constrained to consume less bandwidth and consequently possess less detail. Those readers who know the difference between "luminance" and "luma" should refer to Prime Disclaimer. Except where otherwise noted, we use the two terms interchangeably throughout this web site which usage is not entirely correct.
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