Understanding the Video Signal

This article has two parts: the first part is an excerpt from the “Understanding CCTV Series,” and the other part is an abstract from STAM InSight (IP Australia), which contains the entire CCTV Program on compact disc read-only memory for employee coaching and productivity enhancement.

The Video Signal – The fundamental electrical signal

We will discuss the video signal in this article, which is the fundamental electrical signal that begins at the camera and travels through a transmission system to the room where the video is being displayed. In the world of CCTV, this signal is referred to as Composite Video. It has a maximum amplitude of one V from peak to peak, at its maximum. The various elements of the composite video signal and their respective functions are frequently defended in this manner by us. The following components are assembled to form the composite video:

• Video signal
• Horizontal sync pulse
• Vertical sync pulse

1. Video Signal

When light falls on a CCD chip, it causes a charge to be generated within the pixels, which is directly proportional to the amount of sunlight that falls on them. A large amount of light indicates a larger charge.

Afterwards, the charge is browsed out of the CCD chip, and the charge is transformed back into a video signal. The method by which this charge is read from the chip is dependent on the type of CCD chip being used.

The amplitude of the video signal increases in direct proportion to the number of sunshine rays hitting the pixel. The maximum amplitude of the video signal in a highly composite video is 0.7 volts in an extremely composite video.

As an alternative to this, the white or brilliant part of an image can have a significant strength of zero. In other words, it can be completely white. The signal from the white elements will be 7 volts, whereas the signal from the black or dark elements will be 0 volts.

2. Vertical Sync Pulses.

A video image is created by assembling video frames. Thirty frames per second are displayed in NTSC, whereas twenty-five frames per second are displayed in PAL.

This video frame is divided into two fields, designated as odd and even fields, to prevent picture flicker in CCTV. These two fields are separated for the camera and then combined once more for the monitor’s purpose. This can also be referred to as the interweaving of fields in some circles.

Every frame or field may have a correct vertical pulse added at the end of the structure or area.

When this sync pulse is received, it informs the electronic devices within the camera Associate in Nursing, different CCTV that the sector has come to an end and makes them ready to receive the next frame or field in the sequence.

The heartbeat’s length is determined by the amount of time it takes for the electronic devices to receive the following field. This pulse has an amplitude of 0.3 Vs. and a duration of 1 second. Once this is added to the video signal, it provides a complete amplitude of one volt from peak to peak from start to finish.

3. Horizontal Sync Pulse

NTSC frames contain 525 lines per frame, whereas PAL frames contain 625 lines per frame.

Everything that happens along the line reflects the strength of the video signal.

Every line has a horizontal synchronising pulse added at the beginning of each line.

This sync pulse informs the electronic devices in the CCTV system that a line has returned to the associate in the Nursing end and that they should be ready for when the following line is to be initiated. Additionally, it has an amplitude of 0.3 volts in addition to that.

Some Video Signal’s statistics and additional information you will need to know

1. Horizontal and Vertical Scanning Frequencies

The following tables detail the different frequencies under the PAL and NTSC systems.

• The time required to maneuver from the top of one line to the beginning of the following line or from the end of one field to the beginning of the next field is referred to as the retrace or fly back. Because no image information is scanned throughout the retrace, it is recommended that it be blanked out.

• In television, blanking refers to the process of “achieving a black level.”

• Retracing must be extremely fast because there is so much lost information in the picture during this wasted time period.

• The time required for horizontal blanking is approximately 16 percent of the total time needed for each horizontal line.

• The time needed for vertical blanking is around 8% of the whole standing field time.

2. Horizontal and Vertical Synchronization

In scanning, the blanking pulse places the video signal at the block level, and the synchronisation pulse initiates the specific retrace in the scanning process.

A horizontal sync pulse is inserted into the video signal during the time between the horizontal blanking pulse and the vertical blanking pulse.

A vertical sync pulse is inserted into the video signal between the vertical and the horizontal blanking pulse. The following is that the frequency of each synchronisation pulse is increased.

3. The Color Signal

A colour video signal is the same as a monochrome video signal, except that it includes the colour information contained within the scene, which is transmitted on an individual basis.

The two movements that follow are transmitted one after the other.

• Luminosity signal: also known as the Y signal, contains variations in image information similar to that found in a monochrome call. It is used for breeding the picture in black and white.

• Chrominance signal: Also known as the C signal, this signal contains information about colour and brightness. It is transmitted in the form of modulation on a subcarrier channel. The subcarrier frequency for NTSC is 3.58 megahertz, while the frequency for PAL is 4.43 megahertz.

During the operation of a colour receiver, the chrominance signal is recovered and combined with the luminosity signal to provide a colour image. When using a monochrome receiver, the chrominance signal is not used, and the picture is reproduced in black and white instead of colour.

Composite Video Signal Construction

The following are the segments of the composite video:

• The camera signal output responds well to changes in the amount of sunlight in the scene.

• The scanning is synchronised by the synchronisation pulses.

• The blanking pulses that are used to form the invisible retrace

For colour signals, the chrominance signal and the colour sync burst are both included in the calculation.

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