Video signal

Signalogram of one television line of a video signal. The upper level is “white”; middle level - “black”; the lower level is “blacker than black”. Bold line - video signal, color area - color signal

The video signal is the main component of the television signal . It is a complex broadband electrical signal containing encoded information about a television or facsimile image . In addition, the video signal is used in radar ^[1] .

The concept of video signal is applicable to both analog and digital television, as well as to computer information display systems based on cathode ray tubes .

Content

Video Composition

Sometimes a video signal is considered a signal that carries only information about the brightness of the image, however, the real video signal contains all the service information necessary for the transmission and playback of the image. Any video signal contains ^{[2] a} variable component that carries information about the brightness of image elements, as well as a clock signal ^[3] , consisting of clock pulses, horizontal and frame blanking and equalizing pulses . A full color television signal (PCTS) ^[4], in addition to the video signal, contains a subcarrier modulated by a color signal and contains information about the color of image elements, as well as a color burst signal ^[5] . In television broadcasting, an additional service measurement information is added to the video signal, which is not displayed by standard television receivers and used to adjust the characteristics of the transmitting channel, as well as to transmit teletext or closed captioning . In addition, the video signal often contains a kind of time code - VITC, transmitted during a frame sync pulse . This signal is also invisible on the screen and is used for video editing .

Unplayable Part

The video signal of one line and the duration of its active and non-displayed parts. At the bottom - lowercase sync pulses

A bit more than 70% of the video signal is used to transmit useful image information. The rest of the time is occupied by the transmission of the blanking signal and service information. This ratio is inherited from the first television technologies using cathode ray tubes. The television image in such tubes was built by an electron beam rejected by a special magnetic system, which needed a period of time necessary for the backward beam during frame and line scans.

During the return stroke, the video signal contains a special ^[6] ^[7] quenching pulse, blocking ^{[ how?} ^] electron tube of a kinescope for complete extinction of an electron beam. Otherwise, the image on the screen will be crossed out by a beam making a reverse stroke. For reliable locking of the beam current, the quenching pulses are transmitted at the “black” level ^[8] , that is, the level of the video signal corresponding to the blanking corresponds to the black color of the image. Sync pulses are transmitted at a level “blacker than black”: their level is taken as “0”, then the black level corresponds to 0.3 levels of the full signal, that is, white, equal to one.

The video signal contains horizontal and frame blanking pulses transmitted along with horizontal and frame sync pulses.

Reverse frame scan takes time, corresponding to several lines. Such lines are called passive and do not participate in image construction, but are included in the decomposition standard .

In the European standard 625/50, the reverse scan of the personnel scan takes 49 lines (24 and a half lines per field), so 576 lines of this standard are considered active. American Standard 525/60 contains 483 active lines ^[9] .

With the European standard for decomposition 625/50, the duration of one line is 64 microseconds ^[10] , while its displayed part takes no more than 52 μs., Since the rest of it is occupied by the quenching pulse. Thus, a bit more than 80% of the time is used to transmit an image with horizontal scanning. The same picture develops with a frame scan that uses approximately 92% of the frame duration to transmit active lines.

Notes

↑ Great Encyclopedic Dictionary "Great Russian Encyclopedia", 1991
↑ Full television signal (Russian) . The principle of constructing a television signal . "Operating principle". Date of treatment August 16, 2012. Archived on August 19, 2012.
↑ Television signal (Russian) . "Color television." Date of treatment August 16, 2012. Archived on August 19, 2012.
↑ Parameters of the full television signal (Russian) . "Color television." Date of treatment August 1, 2012. Archived on August 19, 2012.
↑ Signals of color synchronization (Russian) . The principle of image signal formation of color television . "Operating principle". Date of treatment August 16, 2012. Archived on August 19, 2012.
↑ Full television signal (Russian) . The principle of constructing a television signal . "Operating principle". Date of treatment August 16, 2012. Archived on August 19, 2012.
↑ Extinguishing impulses (Russian) . "Color television." Date of treatment August 16, 2012. Archived on August 19, 2012.
↑ Structural diagram of a black-and-white image transmission system (Russian) . The basics of television . Date of treatment August 16, 2012. Archived on August 19, 2012.
↑ Worldwide broadcast television. Standards and Systems, 2004 .
↑ Scan parameters (Russian) . The principle of constructing a television signal . "Operating principle". Date of treatment August 16, 2012. Archived on August 19, 2012.

Literature

A.E. Peskin, V.F. Trufanov. World Broadcast Television. Standards and systems . - M.,: “Hot line - Telecom”, 2004. - 308 p. - ISBN 5-93517-179-1 . (inaccessible link)

V.E. Dzhakonia. Tv - M.,: “Hot line - Telecom”, 2002. - S. 41-56. - 640 s. - ISBN 5-93517-070-1 .

[1] Great Encyclopedic Dictionary "Great Russian Encyclopedia", 1991

[2] Full television signal (Russian) . The principle of constructing a television signal . "Operating principle". Date of treatment August 16, 2012. Archived on August 19, 2012.

[3] Television signal (Russian) . "Color television." Date of treatment August 16, 2012. Archived on August 19, 2012.

[4] Parameters of the full television signal (Russian) . "Color television." Date of treatment August 1, 2012. Archived on August 19, 2012.

[5] Signals of color synchronization (Russian) . The principle of image signal formation of color television . "Operating principle". Date of treatment August 16, 2012. Archived on August 19, 2012.

[6] Full television signal (Russian) . The principle of constructing a television signal . "Operating principle". Date of treatment August 16, 2012. Archived on August 19, 2012.

[7] Extinguishing impulses (Russian) . "Color television." Date of treatment August 16, 2012. Archived on August 19, 2012.

[8] Structural diagram of a black-and-white image transmission system (Russian) . The basics of television . Date of treatment August 16, 2012. Archived on August 19, 2012.

[_7aec8bca48e687cc-9] Worldwide broadcast television. Standards and Systems, 2004 .

[10] Scan parameters (Russian) . The principle of constructing a television signal . "Operating principle". Date of treatment August 16, 2012. Archived on August 19, 2012.