Radiometric units
Units (W/m, J, etc.) that are used to measure the quantity of electromagnetic radiation. Contrasts with photometric units (used for the measurement of visible light), which take into account the sensitometric characteristics of the human eye. See also Photometric units, Color temperature.

Raster
The sequential scanning pattern used in video that dissects the image in the pickup device and lays down the picture in the display device.

Raster line removal
See Scan line removal.

Real time
Video display that occurs at 30fps (RS-170) and 25fps for (CCIR) video synchronization.

Red, green, and blue
See RGB.

Registration
The proper overlapping of the red, green, and blue electron beams in a color pickup tube, CCD, or monitor, to form a correctly colored picture. See also Convergence.

Resolution
A measure of how fine a detail can be detected, in terms of distance in space or passage of time. Note that the convention used to measure spatial resolution in video is every black and white line counted, giving the term "TV lines."

Responsivity
Similar to sensitivity; a rating of the output current from a camera tube or CCD divided by the incident flux of light, usually expressed in signal current per watt of input radiation at a specific wavelength.

Retrace
See Flyback.

RGB (red, green, and blue)
A form of color video signal, or type of color camera or monitor. Does not use an encoded signal such as NTSC, which can be transmitted over a single cable or channel, but instead uses three separate cables for carrying R, G, and B signals. Without the loss due to encoding and decoding, the picture quality and resolution of an RGB system is superior to encoded color video.

RGB-sync, RGBY
Forms of RGB color video signals that require a fourth connection to carry a separate sync signal (RGB-sync) or luma signal (RGBY).

Ringing
An oscillatory transient that occurs as a result of a sudden change in input. In video monitors, ringing gives rise to narrow, reversed-contrast stripes to the right of sharp vertical lines or edges.

Rise time
The transient response of an electronic device or circuit to a rising square wave pulse. The rise time is measured as the time interval that elapses between a 10% and 90% rise of the steady-state value.

rms (root mean squared)
A method of expressing the amplitude of a signal in relation to its energy. For sine wave signals, its rms value is given by (peak amplitude/ /2 ).

Roll
A loss of vertical synchronization, causing the video picture to spontaneously flip or slip, up or down, on a monitor.

Root mean squared
See rms.

RS-170
The 525/60, 2:1 interlace standard format recommended by EIA for broadcast monochrome video in the United States. For color, the temporary standard RS-170A is used. For closed circuit, TV RS-170 is common, but other formats including RS-330 are also used.

RS-232C
A standard recommended by EIA specifying basic guidelines for a class of relatively slow (up to 20,000 baud), serial, communications links between computers and peripherals. In RS-232C, up to 25 data lines are available but only 3-5 are used.

RS-330
A standard recommended by EIA for signals generated by closed-circuit TV cameras scanned at 525/60 and interlaced 2:1. The standard is more or less similar to RS-170, but H-sync pulses are absent during V-sync. Equalizing pulses are not required and may be added optionally during the V-blanking interval.

RS-343A
EIA standards for high resolution monochrome CCTV.

Saticon
A vidicon-type image pickup tube. Exhibits low lag, high resistance to blooming, low dark current, near-unity gamma, and well-balanced spectral sensitivity. Popular for use in color cameras.

Saturation
In color, the degree to which a color is undiluted with white or is pure. The vividness of a color, described by such terms as bright, deep, pastel, pale, etc. Saturation in the color video signal increases proportionately with the amplitude of the chrominance signal. In black and white, the degree which the white signal is compressed and high light detail is lost.

Scan
The act of moving the video charge out of the detector. As in a CCD or solid state array where the charge is moved out of the array by clocking a potential from pixel to pixel, or by an electron beam moving across the detector in an image pickup tube. Also the movement of the electron beam across a cathode ray tube in a monitor.

Scan rate
The number of horizontal lines per frame and vertical scans per second that are repeated in video; e.g., 525/60, 625/50. In 525/60, 2:1 interlaced video, the V-scan is repeated at the field rate (which is half of the frame rate for 2:1 interlaced video) so that 525 H-scans take place 30 times per second. The H-scan rate is therefore 525 X 30 = 15.75kHz. With 525/60, 1:1 interlace, the H-scan rate would be twice this value.

Scope
Short for cathode ray oscilloscope. See Cathode ray oscilloscope.

Scroll
Movement of the video picture up or down the video screen at a moderate, even pace to expose the lower or upper portions of a scene that previously were not visible.

Sensitivity
Similar to responsivity of a camera tube or CCD but numerically different. It is the signal current per unit of illuminance on the faceplate in lumens. It is expressed in amps/lumen. Unless otherwise specified, the radiation is understood to be that of an unfiltered incandescent source at 2856 degrees K. See also Responsivity, Light transfer characteristics.

Serrations
The horizontal timing pulses that appear as positive-going notches in the negative-going vertical sync pulse in some timing signals. While the polarity of the serration pulses are reversed from the equalizing pulses, it is still the negative-going voltage change that signals the start of an H interval.

Setup
In a video picture signal, the difference between the black and blanking levels expressed in IEEE units. Also the ratio (expressed in percentages) of this value to the difference between the reference white and blanking levels.

Seventy-five ohm cable
A coaxial cable commonly used to carry video signals. The characteristic impedance of the cable for a signal frequency greater than 4kHz is 75 ohms.

Shading
A large-area brightness gradient in the video picture, not present in the original scene.

Shading compensation
Dynamic sensitivity control of the picture signal found in some precision video cameras and monitors. The compensation reduces the amount of change in the video level from center to edge, or edge to edge of the picture. Shading can also be compensated during analog or digital image processing by adding suitable waveforms, or by subtraction of, or division by, the background image.

Signal-to-noise ratio (S/N ratio)
In video, the ratio of the peak amplitude of the signal to the rms value of the noise. Usually expressed in decibels. The higher the S/N ratio, the cleaner the video picture.

Silicon
Also Silicon vidicon, S-T vidicon. Short for silicon target vidicon tube. (Not the same as SIT.) The Silicon is a vidicon-type camera tube with a silicon target having a very high sensitivity in the near infrared. Has quite good resolution but is subject to blooming. See also Ultricon.

Silicon Intensifier Target tube
See SIT.

Silicon Target Vidicon
See Silicon.

SIT (Silicon Intensifier Target tube)
A video camera tube of the direct readout type designed for low-light applications. Has a silicon target and an integral intensifier section, with direct electron input to the silicon target. Not the same as silicon target vidicon tube or ISIT. Has high sensitivity, good resolution, but under very low-light input conditions exhibits considerable lag. See also p-n junction diode.

Slave
A piece of video equipment whose synchronizing signals are derived from another piece of equipment that serves as the sync source.

Slow scan
A system of video scanning in which the time used to read each line has been increased in comparison to standard video. The bandwidth needed to faithfully transmit or record the signal is reduced in inverse ratio to the scanning time. Slow scan allows the video signal to be transmitted over a telephone line, or line scans to be registered on a chart recorder without loss of spatial resolution.

Slow scan CCD
A CCD image detector which has special circuits allowing for readout of the information at slower than standard video rates to reduce readout noise.

S/N (signal to noise ratio)
Also sometimes used as an abbreviation for serial number; can be somewhat confusing in the case of electronic equipment. See Signal to noise ratio.

Snow
Heavy random noise seen on the video screen. May arise from the camera at low light levels or defective cables or connectors.

Solid-state device
Also Solid-state sensors. In video, image pickup devices that use solid-state sensors such as CCD, CID, etc., rather than vacuum-tube-type sensors such as vidicons or intensifier camera tubes.

Solid-State sensors
See Solid-state device.

Spatial frequency
The frequency in space in which a recurring feature appears, e.g., 20 line pairs/mm. In a video signal, spatial frequency along the horizontal axis is proportional to 1/(time interval between the recurring signal) or to frequency (Hz, MHz, etc.) of the electrical signal.

Spectral response curve
In a photodetector, the curve that relates the electrical current or voltage, generated per unit power input for various wavelengths of light. Usually displayed in Amps/Watt per unit wavelength.

Spike
In electronics, a sharp brief voltage pulse. Powerful RF spikes that can damage video equipment and computers are generated when mercury or xenon arc lamps are started. To a limited extent, spikes entering through the power line (but not those rated as RF) can be suppressed with spike arrestors (transient suppressors).

Square wave response curve
Also CTF. See Modulation transfer function.

Standard signal
A signal whose peak-to-peak voltage is appropriate for the system. For EIA RS-170, RS-330, and CCD composite signals, it is 1.0 Vpp; for noncomposite picture signals, 0.7 Vpp; and for sync-only signals, .3V.

Streaking
Also Reverse polarity smear. In video, a picture condition in which very bright or dark objects appear to be extended horizontally beyond their normal boundaries, often in reverse contrast. May arise in the camera, in overdriven amplifiers, or by improper adjustments of the monitor's Contrast and Brightness controls.

S-T vidicon
See Silicon.

Sulfide vidicon
See Vidicon.

Sync (synchronization)
The H and V timing pulses that drive the video scanning system. Also the act of synchronizing. See Sync pulse.

Sync generator
An electronic circuit or device that produces the sync pulses for the H and V drives in video. See Sync.

Sync level
The level of the tips of the video synchronizing signals.

Sync pulse
Also Sync signal. The sharp square-wave pulses whose leading edges are used to synchronize the video scanning, blanking, etc.

Sync signal
See Sync pulse.

Sync source
A piece of video equipment that provides the sync signals that drive other (slave) video equipment in synchrony.

Sync stripper
A video circuit or device that separates the sync signal from the picture signal in a composite video signal. After the sync pulses are reshaped, they are made available for further use.

Sync tip
The levels of the tips of the H and V sync pulses. In EIARS-170 and RS-330 video signals, the level of the sync tip with proper termination is specified to be -40 IEEE units, or -0.3 V.

Target
In video image pickup tubes, the light sensitive structure deposited on the faceplate of the tube. Scanned by the electron beam, the target generates a signal output current corresponding to the charge density pattern formed there by the optical image. The target usually includes: the photoconductive storage surface, which is scanned by the electron beam; the transparent, conductive backplate (target electrode); and the intervening dielectric.

Target integration
A means of increasing the sensitivity and reducing the noise of a low-light-level scene in a video camera when viewing a static scene. The beam is shut off for a predetermined number of frames and read out in the first frame after the beam is turned back on. In vidicon tubes, the target automatically integrates the signal for 16.7 msec at standard scanning rates.

Temporal resolution
The ability to resolve time-related events, i.e., the use of electronic shuttering and gating to capture time-dependent events.

Termination
The insertion, or presence, of a proper load at the end of a signal cable. For closed circuit TV, an impedance of 75 ohms provides proper termination and impedance matching for commonly used video equipment and cables. An improperly terminated end of a cable can reflect the signal back as an echo and also alter the signal voltage.

Three chip color camera
A color video camera that uses beam splitters, three color filters, and CCDs to independently register the R, G, and B components of the image spectrum. The output can be an RGB signal or an encoded NTSC signal.

Threshold
The signal that can just barely be recognized or that gives a certain percentage of affirmative response in psychological testing. A high threshold signifies a lower sensitivity.

True color camera
A camera specifically designed to reproduce the spectral response of the human eye.

Two-to-one interlace
See Interlace. Also see Noninterlace, Random interlace.

Ultricon
An improved type of Silicon vidicon that has very high sensitivity in the near infrared and good resolution. It is less subject to blooming of the image highlights than standard Silicons, but not quite immune to blooming.

Underscan
The display of the entire video picture by shrinking the scan area on a monitor. See also Overscan.

Usable light range
The ratio of the maximum to the minimum levels of illuminance over which a video camera or camera tube can provide a usable signal. Being aided by automatic irises, gray wedge wheels, etc., in addition to varying electrode voltages where permissible, the usable light range can be several orders of magnitude greater than the intrascene dynamic range. See also Intrascene dynamic range.

V blank
Also Vertical blanking, Field blanking. The voltage that suppresses the beam current during vertical retrace in the camera tube and monitor; also the time interval of the V blank. V and H sync pulses and other signals that are not displayed on the monitor are added during this interval. See also Flyback.

Vertical blanking
See V blank.

Vertical frequency
The number of video fields scanned every second: 60 Hz for monochrome in the 525/60, 2:1 interlace format; 59.4 Hz for color video in the NTSC format.

Vertical resolution
The number of black and white horizontal lines per picture height that can be resolved vertically on the video monitor or in a video signal. Commonly, vertical resolution is given by the number of active H scan lines x the Kell factor, but is somewhat less for random interlace video. See also Horizontal resolution.

Vertical retrace
At the end of each field scan in a video camera or picture tube, the returning of the scanning beam from the bottom of the picture to the beginning position of a new vertical scan. Also the time interval for the V retrace, which takes place over 12-15 H scan intervals. Thereafter, the first several lines of the new V scan are still hidden at the top of the picture until the V blank ends. See also Flyback, V blank.

Vertical scan (V scan)
In raster scanned video, the slow, downward (as seen on the monitor) deflection of the electron beam that makes each active H scan appear in succession below the previous line. In NTSC video, the V scans alternate 60 times a second with the starting phases 0.5 H apart, thus giving rise to the odd and even fields. See also Scan, H scan, Scan rate.

Vertical sync pulse (V sync pulse)
The negative-going, V-timing pulse that occurs during the V blank interval in a composite video signal. The pulse triggers the vertical sweep generator in the monitor. In the NTSC color signal, the V sync pulse, which is 3 H long, is interrupted by six serrations.

V hold (Vertical hold)
The control on a video monitor or TV set that is used to adjust vertical sync and proper interlace of the scan lines. See also Interlace.

Video
The picture portion of TV, as contrasted to audio.

Video gain
The control on a video camera, monitor, processor, SEG, TBC, etc., that allows the user to alter the amplitude of the video picture signal. Results in a change in picture contrast and brightness.

Video in
The input connector for the video signal. Contrasts with Video out, except in a video monitor where the two are connected E-to-E and can be used interchangeably.

Video microscopy
Microscopy that takes advantage of video as an imaging, image processing, analyzing, or controlling device.

Video out
The connector on a piece of video equipment that provides an output of a composite video signal. When properly terminated, the full EIA RS-170, RS-330, CCIR or NTSC signal should measure 1 Vpp.

Video waveform
The display of the (composite) video signal onto a cathode-ray oscilloscope triggered by the V and H sync pulse. The amplitudes and waveforms, as well as precision of timing of the signal components are made visible.

Vidicon
Refers to the standard, or sulfide, vidicon tube, rather than to a family of vidicon-type camera tubes. Using antimony trisulfide as the photoconductive element in the target, the Vidicon has a relatively low sensitivity and high dark current, but high resolution, AGC compatibility, and low gamma. The low gamma signifies nonlinear response to light, but also results in a high dynamic range.

Vidicons
A family of video camera tubes in which an electrical charge density pattern is formed by photoconduction in the target and stored there. The signal current is generated as the electron beam scans the target in a raster. Includes the standard (sulfide) Vidicon, as well as the Newvicon, Chalnicon, Plumbicon, etc.

Vignetting
An unintentional, shaded loss of the edges of an image or picture by an optical component clipping the peripheral beams can lead to loss of contrast in video.

Vpp
Volts peak-to-peak. See Peak-to-peak.

V scan
See Vertical scan.

V sync pulse
See Vertical sync pulse.

Waveform monitor
A cathode-ray oscilloscope that can conveniently display the video signal. See also Video waveform.

White balance
A color video camera circuit that allows simple adjustment of the RGB signals to produce a correctly balance white. It is activated by pointing the camera to a reference white surface and pressing the white balance button.

White compression/clipping
Amplitude compression/clipping of the signals in the brighter regions of the picture. Results in differential gain that expands the dark and middle regions of the gray scale.

White level
Also Reference white level. The IEEE scale, or voltage level, of the video picture signal that corresponds to a specified maximum limit for white peaks.

White peak
Also Maximum white. The highest amplitude or peak in white reached by the video picture signal; measured in IEEE scale or voltage.

White punch
Reversing the polarity of video signals at very high levels of white. Very bright areas are displayed increasingly darker inside a white rim.

Y
Symbol for the luminance portion of the picture signal in NTSC video.

Yoke
The assembly of electromagnetic coils that are placed over the camera tube, or the neck of a picture tube or a cathode-ray tube of the magnetic focusing type. The focusing coil in the yoke controls the convergence of the electron beam. The H and V deflection coils deflect the electron beam so that it sweeps the target or phosphor in a standard video raster.