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Các khái niệm cơ bản về Camera

Các kiến thức cơ bản về Camera
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Các kiến thức cơ bản về Camera
WDR (Wide Dynamic Range)
Digitally adjusting exposure in areas of the frame to maintain optimum detail in both the shadows and highlights of the image.


TVL (TV Lines)
Analog surveillance video resolution is measured in terms of broadcast TV lines as viewed on a monitor screen. Video quality is charted with converging lines of higher and higher density. The TVL resolution number is the line density where the camera is no longer able to reproduce individual lines. The higher this number is, the better the picture.


The digital recording resolution can be expressed in effective pixel dimensions.

Typical pixel dimensions:

            480 TVL                            510 x 492               
600 TVL 768 x 494
650 TVL 811 x 508
700 TVL 976 x 582

SLR (Strong Light Reduction)

Sometimes also called HLC (High Light Compensation), SLR is the masking of a very intense light source such as car headlights in order to bring up detail in the normally lit areas, such as a license plate or face.


A camera function allowing the user to select a slower shutter speed in order to let extra light into a camera. This provides higher sensitivity in low light conditions and may eliminate the need for artificial light.


The resolution of a surveillance camera’s image is measured in the number of pixels contained in the image. The higher the number of pixels, the more detail in the image. Higher resolution images give you the ability to zoom into the image to see fine detail.

Typical Resolutions

  • VGA: 640 x 480
  • D1: 720 x 480
  • Full D1 (FD1), 960H: 960 x 480
  • 720p: 1280×720
  • 1.3 MegaPixel: 1280×1024
  • 1080p, 2.1 MegaPixel: 1920×1080
  • 3 MegaPixel: 2048×1536
  • 5 MegaPixel: 2592×1920
  • 6 MegaPixel: 3072×2048


(Images are for illustrative purposes only and are not actual camera images)

A 1080p image has more than 6 times the number of pixels as a VGA image.

Real Time

DVRs that display and record at the full frame rate of 30 fps per channel of video are called “real time.”
Many DVRs do not have the processing capability to record in real-time. They record only intermittent frames coming from the camera. A full frame rate produces the smoothest, clearest picture.
A DVR usually specifies the total frame rate for all channels. If you have a 4 channel DVR with a total frame rate of 120 fps, each channel records at 30 fps which means it can record in real time.

PoE (Power over Ethernet)

The feature of providing both data and power over the one ethernet cable, eliminating the need for a separate power cable.
PIR (Passive Infrared):
A passive infrared sensor is often used in motion detectors. Motion is detected when an infrared source with one temperature, such as a human, passes in front of an infrared source with another temperature, such as a wall. The sensor does not dectect the “heat” from the object passing in front of it. Instead it detects that the object breaks the field which the sensor has determined as the “normal” state. Any object, even one exactly the same temperature as the surrounding objects will cause the PIR to activate if it moves in the field of the sensors.
The term passive means that the PIR device does not emit an infrared beam but merely passively accepts incoming infrared radiation.
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