GLOSSARY OF TERMS USED IN VIDEO ENGINEERING

There are certain terms that are very important in video engineering and very much used to represent many properties of an video signal.

Aspect Ratio

The ratio of the visible-picture width to the height. Standard television and computers have an aspect ratio of 4:3(1.33). HDTV has aspects ratios of either 4:3 or 16:9(1.78). Additional aspect ratios like 1.85:1 or 2.35:1 are used in cinema.

Back Porch

The area of a composite video signal defined as the time between the end of the color burst and the start of active video. Also loosely used to mean the total time from the rising edge of sync to the start of active video.

Blanking Interval

There are horizontal and vertical blanking intervals. Horizontal blanking interval is the time period allocated for retrace of the signal from the right edge of the display back to the left edge to start another scan line. Vertical blanking interval is the time period allocated for retrace of the signal from the bottom back to the top to start another field or frame. Synchronizing signals occupy a portion of the blanking interval.

Blanking Level

Used to describe a voltage level (blanking level). The blanking level is the nominal voltage of a video waveform during the horizontal and vertical periods, excluding the more negative voltage sync tips.

Breezeway

The area of a composite video signal defined as the time between the rising edge of the sync pulse and the start of the color burst.

Chroma

The color portion of a video signal. This term is sometimes incorrectly referred to as "chrominance," which is the actual displayed color information.

Clamp

A circuit that forces a specific portion (either the back porch or the sync tip) of the video signal to a specific DC voltage, to restore the DC level. Also called "DC restore." A black level clamp to ground circuit forces the back-porch voltage to be equal to zero volts. A peak clamp forces the sync-tip voltage to be equal to a specified voltage.

Color Bars

A standard video waveform used to test the calibration of a video system. It consists of a sequence of the six primary and secondary colors plus white with a standard amplitude and timing. The active-low color sequence is white, yellow, cyan, green, magenta, red, and blue. There are several amplitude standards, the most common being 75% amplitude (brightness) with 100% saturation (intensity of the color).

Color Burst

The color burst, also commonly called the "color subcarrier," is 8 to 10 cycles of the color reference frequency. It is positioned between the rising edge of sync and the start of active video for a composite video signal.

Color Saturation

The amplitude of the color modulation on a standard video signal. The larger the amplitude of this modulation, the more saturated (more intense) the color.

Color Subcarrier

See Color Burst. 

Component Video

A three-wire video interface that carries the video information in its basic RGB components or luma (brightness) and two-color-difference signals.

Composite Video

A video signal that combines the luma (brightness), chroma (color), burst (color reference), and sync (horizontal and vertical synchronizing signals) into a single waveform carried on a single wire pair.

Differential Gain

Important measurement parameter for composite video signals. Not applicable in Y/C or component signals. Differential gain is the amount of change in the color saturation (amplitude of the color modulation) for a change in low-frequency luma (brightness) amplitude. Closely approximated by measuring the change in the amplitude of a sine wave for a change in its DC level.

Differential Phase

Important measurement parameter for composite video signals. Not applicable in Y/C or component signals. Differential phase is the change in hue (phase of the color modulation) for a change in low-frequency luma (brightness) amplitude. Closely approximated by measuring the change in the phase of a sine wave for a change in its DC level.

Fields and Frames

A frame is one complete scan of a picture. In NTSC it consists of 525 horizontal scan lines. In interlaced scanning systems, a field is half of a frame; thus, two fields make a frame.

Front Porch

The area of a composite video waveform between the end of the active video and the leading edge of sync.

Horizontal Blanking

See Blanking Level and Blanking Interval. 

Horizontal Line Frequency

The inverse of the time (or period) for one horizontal scan line.

Interlaced Scan

The process whereby each frame of a picture is created by first scanning half of the lines and then scanning the second set of lines, which are interleaved between the first to complete the picture. Each half is referred to as a field. Two fields make a frame.

IRE

An arbitrary unit of measurement equal to 1/100 of the excursion from blanking to reference white level. In NTSC systems, 100 IRE equals 714mV and 1-volt p-p equals 140 IRE.

Luma

The monochrome or black-and-white portion of a video signal. This term is sometimes incorrectly called "luminance," which refers to the actual displayed brightness.

Monochrome

The luma (brightness) portion of a video signal without the color information. Monochrome, commonly known as black-and-white, predatescurrent color television.

NTSC

National Television Systems Committee. A group that established black-and-white television standards in the United States in 1941 and later added color in 1953. NTSC is used to refer to the systems and signals compatible with this specific color-modulation technique. Consists of quadrature-modulated color-difference signals added to the luma with a color subcarrier reference of 455/2 times the horizontal line rate, typically 3.579545MHz with an H rate of 15.75kHz. Commonly used in 525-line, 59.94Hz scanning systems.

PAL

Phase alternate line. PAL is used to refer to systems and signals that are compatible with this specific modulation technique. Similar to NTSC but uses subcarrier phase alternation to reduce the sensitivity to phase errors that would be displayed as color errors. Commonly used with 626-line, 50Hz scanning systems with a subcarrier frequency of 4.43362MHz.

Pixel

Picture element. A pixel is the smallest piece of display detail that has a unique brightness and color. In a digital image, a pixel is an individual point in the image, represented by a certain number of bits to indicate the brightness.

Progressive Scan

The process whereby a picture is created by scanning all of the lines of a frame in one pass. See also Interlaced Scan. The process of converting from interlaced to progressive scan is called "line doubling."

Raster

The collection of horizontal scan lines that makes up a picture on a display. A reference to it normally assumes that the sync elements of the signal are included.

Refresh Rate

See Vertical Frame Rate. 

RGB

Stands for red, green, and blue. It is a component interface typically used in computer graphics systems.

Setup

A reference black level 7.5% (7.5IRE) above blanking level in NTSC analog systems. It is not used in PAL or digital or HDTV systems. In these systems, reference black is the same level as blanking.

Subcarrier

See Color Burst. 

S-Video

Commonly incorrectly used interchangeably with Y/C. See also Y/C. Technically, a magnetic-tape modulation format. 

Sync Signals/Pulses

Sync signals, also known as sync pulses, are negative-going timing pulses in video signals that are used by video-processing or display devices to synchronize the horizontal and vertical portions of the display.

Vertical Blanking

See Blanking Level and Blanking Interval. 

Vertical Field Frequency

The inverse of the time (or period) to produce one field of video (half of a frame). In NTSC it is 59.94Hz.

Vertical Frame Rate

The inverse of the time (or period) to produce one frame of video. Also called "refresh rate" or "vertical refresh rate."

Video Bandwidth, Minimum

The minimum analog bandwidth required to reproduce the smallest amount of detail contained in the video signal.

Y Cr Cb

A digital component video interface. Y is the luma (brightness) portion, and Cr and Cb are the color-difference portions of the signal.

Y Pr Pb

An analog-component video interface. Y is the luma (brightness) portion, and Pr and Pb are the color-difference portions of the signal. Typically used on high-end consumer video equipment.

Y/C

An analog video interface in which the chroma (color) information is carried separately from the luma (brightness) and sync information. Two wire pairs are used, denoted Y and C or Y/C. Often incorrectly referred to as "S-video."