Frame blanking pulse

Fragments of personnel blanking pulses of odd and even fields. Equalizing pulses and frame sync pulses are visible.

Frame blanking pulse ( Eng. Vertical Blanking Interval , abbreviated VBI ), also known as VBLANK - a component of the video signal of analog television , existing to cancel the kinescope beam during the reverse motion ^[1] frame scan . Each interlaced video frame contains two frame blanking pulses, one for even and odd fields . With progressive scan, the frame contains one frame blanking pulse. The frame blanking pulse and its components are formed by the synchro-generator of a video camera , VCR or computer video card .

Content

History

The blanking pulse is inherited by modern television from earlier cathode ray tube systems. Its duration is significant due to the inductive inertia of the deflecting magnetic coils, which carried out horizontal and frame sweeps, deflecting the electron beam. The magnetic field , and therefore the position of the luminous point on the screen, cannot change instantly, so the return stroke takes a certain period of time. For frame scanning, it is equal to the duration of several lines of horizontal scanning, since the generators of both scan work continuously. Lines falling on the reverse frame scan do not carry images and are therefore called passive. Different designations of decomposition standards may take into account the number of all lines or only active. So, in the European decomposition standard 625/50, adopted in Russia , active lines 576, and 49 - passive, occurring on both frame blanking pulses with a duration of 1.6 milliseconds each ^[2] . Designation 576i is compliant with interlaced 625/50 standard. Modern televisions that are not equipped with cathode ray tubes do not require time to reverse the sweeps, however, analog television standards exist unchanged for the possibility of receiving television programs by all televisions, including with a kinescope .

Composition of a blanking pulse

Together with the frame blanking pulses , frame sync pulses as well as equalizing pulses for interlacing synchronization are transmitted ^[3] ^[4] . The frame blanking pulse is one of the main components of the television clock signal, and in addition to the video signal, television is present in the video signal of analog computer video interfaces, such as VGA , S-Video and others ^[5] ^[6] . The VGA interface for transmitting frame blanking pulses has a separate contact. During the frame quenching pulse, the image is not transmitted and on the screen it is not displayed at all, because it coincides with the reverse course of the scan ^[7] . During the return stroke in the cathode ray tubes, the beam is extinguished to prevent the image from being crossed out. For reliable beam blanking, the frame blanking pulse is transmitted at a level corresponding to the black level in the image ^[8] . During the frame blanking pulse in modern television, service signals can also be transmitted, since the pulse is invisible on the screen. Service information, equalizing and personnel clock pulses are transmitted at a level “blacker than black”. In interlaced scanning, blanking pulses begin at the beginning of the line in the odd half frame and from the middle of the line in the even half frame. The composition and characteristics of the personnel quenching pulses are determined by international agreements adopted to ensure the compatibility of various devices and the international exchange of television programs. In modern analogue television, the blanking parameters are normalized in accordance with the recommendation of ITU BT.1700 ^[9] .

Service Information

In analog and digital television broadcasting systems, a blanking pulse is used to transfer service data, since they are not displayed on the screen and have a long duration sufficient to transmit several kilobits of information. A standard television signal during a frame blanking pulse transmits special measuring lines designed to control the parameters of the transmission channel. The 23rd line per pulse time contains a 14-bit WSS code ( Wide Screen Signaling ), which carries information about the aspect ratio of the image and additional screen porridge ^[10] . Also, closed captioning , teletext , copy protection codes, and other data encrypted with the XDS protocol (for example, ratings for V-chip ^[11] ) can be transmitted in a frame pulse. In addition, the frame blanking pulse is used during video recording for a special kind of time code - VITC - recorded instead of a pulse ^[12] . Transmission of horizontal sync pulses during the frame does not stop to avoid horizontal sync failure. Therefore, the frame blanking pulse has a complex shape and it contains horizontal sync pulses and equalizing pulses ^{[13] with a} duration of 2.35 microseconds ^[14] . The latter are intended for the exact combination of rasters of even and odd interlaced fields. In the SECAM color television system , color recognition signals are also transmitted during the blanking pulse, the presence of which reduces the time for transmitting service information (see Teletext article).

Other uses

In video games, vertical pulses are also used for synchronization. Most of the graphic operations on game consoles, including the 16-bit era, could only be performed during a frame blanking pulse (which programmers often called VBLANK), requiring programs to perform all graphics processing exclusively during this time. The need for synchronization in game code has made programming difficult for early game systems like the Atari 2600 . Computer graphics most often use standards other than television for display, for example, decomposition standards for computers differ in the direction of higher resolution and progressive scanning is possible. Therefore, the frame blanking pulse may vary in duration, and be unique in each frame, but it is mandatory in analog video interfaces designed for monitors with a cathode ray tube.

Most household video recorders use a frame blanking level to set the recording level. The Macrovision protection system against unauthorized copying ^[15] inserts false sync pulses into the frame interval that do not allow the VCR recording level automatic control system to work normally, and disrupts the synchronization of the resulting copy. As a result, copying videos with normal quality becomes impossible.

Notes

↑ Clock selector (Russian) . Teleradio. Date of treatment August 15, 2012. Archived on August 18, 2012.
↑ 1.2 Structure of a television signal (Russian) . Basic information about the television signal . "Observatory". Date of treatment August 15, 2012. Archived on August 18, 2012.
↑ Extinguishing impulse (Russian) . TSB. Date of treatment August 15, 2012. Archived on August 18, 2012.
↑ Equalizing impulses (Russian) . TSB. Date of treatment August 15, 2012. Archived on August 18, 2012.
↑ Synchronization signal (Russian) . The principle of constructing a television signal . "Operating principle". Date of treatment August 15, 2012. Archived on August 18, 2012.
↑ Sync generator (Russian) . SITE ABOUT PC "SPECIALIST" AND ITS CLONES. Date of treatment August 15, 2012. Archived on August 18, 2012.
↑ Parameters of the full television signal (Russian) . "Color television." Date of treatment August 15, 2012. Archived on August 18, 2012.
↑ Structural diagram of a black-and-white image transmission system (Russian) . Date of treatment August 15, 2012. Archived on August 18, 2012.
↑ Characteristics of composite video signals for standard analog television systems (Russian) . RECOMMENDATION ITU-R BT.1700 . ITU (February 2005). Date of treatment December 11, 2012. Archived December 16, 2012.
↑ Keith Jack. Widescreen Signaling (WSS) Application Note AN9716.1 . Intersil (August 1998). Date of treatment January 3, 2015.
↑ What is the V-Chip? (eng.) . Family Safe Media. Date of treatment August 15, 2012. Archived on August 18, 2012.
↑ Field time code (Russian) . Kramer electronics. Date of treatment August 15, 2012. Archived on August 18, 2012.
↑ Equalizing impulses // Great Soviet Encyclopedia : [in 30 vol.] / Ch. ed. A.M. Prokhorov . - 3rd ed. - M .: Soviet Encyclopedia, 1969-1978.
↑ Television signal (Russian) . Satland. Date of treatment August 13, 2012. Archived August 18, 2012.
↑ MACROVISION (Russian) . Date of treatment August 15, 2012. Archived on August 18, 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 .

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

“Peter Norton's® Inside the PC, Seventh Edition.” , Sams Publishing [Indianapolis] Copyright ©, 1997 [and translated by “BHV - St. Petersburg, 1999]. ISBN 0-672-31041-4 (English), ISBN 5-7791-0111-6

[1] Clock selector (Russian) . Teleradio. Date of treatment August 15, 2012. Archived on August 18, 2012.

[2] 1.2 Structure of a television signal (Russian) . Basic information about the television signal . "Observatory". Date of treatment August 15, 2012. Archived on August 18, 2012.

[3] Extinguishing impulse (Russian) . TSB. Date of treatment August 15, 2012. Archived on August 18, 2012.

[4] Equalizing impulses (Russian) . TSB. Date of treatment August 15, 2012. Archived on August 18, 2012.

[5] Synchronization signal (Russian) . The principle of constructing a television signal . "Operating principle". Date of treatment August 15, 2012. Archived on August 18, 2012.

[6] Sync generator (Russian) . SITE ABOUT PC "SPECIALIST" AND ITS CLONES. Date of treatment August 15, 2012. Archived on August 18, 2012.

[7] Parameters of the full television signal (Russian) . "Color television." Date of treatment August 15, 2012. Archived on August 18, 2012.

[8] Structural diagram of a black-and-white image transmission system (Russian) . Date of treatment August 15, 2012. Archived on August 18, 2012.

[9] Characteristics of composite video signals for standard analog television systems (Russian) . RECOMMENDATION ITU-R BT.1700 . ITU (February 2005). Date of treatment December 11, 2012. Archived December 16, 2012.

[10] Keith Jack. Widescreen Signaling (WSS) Application Note AN9716.1 . Intersil (August 1998). Date of treatment January 3, 2015.

[11] What is the V-Chip? (eng.) . Family Safe Media. Date of treatment August 15, 2012. Archived on August 18, 2012.

[12] Field time code (Russian) . Kramer electronics. Date of treatment August 15, 2012. Archived on August 18, 2012.

[13] Equalizing impulses // Great Soviet Encyclopedia : [in 30 vol.] / Ch. ed. A.M. Prokhorov . - 3rd ed. - M .: Soviet Encyclopedia, 1969-1978.

[14] Television signal (Russian) . Satland. Date of treatment August 13, 2012. Archived August 18, 2012.

[15] MACROVISION (Russian) . Date of treatment August 15, 2012. Archived on August 18, 2012.