CCTV CAMERA RESOLUTION - TVL - Television Lines explained
Resolution is the quality of definition and clarity of a picture and is defined in lines
meaning more lines = higher resolution , means better picture quality.
The Resolution depends on the amount of pixels (picture elements) in the CCD chip. If a camera manufacturer can put in more number of pixels in the same size CCD chip, that camera will have a higher resolution. In other words the resolution is directly proportional to the number of pixels in the CCD (Charge Coupled Device) chip.
In many data sheets, two type of resolution, vertical and horizontal are indicated.
Vertical resolution stands for the number of horizontal lines
The Vertical Resolution is limited by the number of horizontal scanning lines. In PAL it is 625 lines and in NTSC it is 525 lines. Using the Kell or aspect ratio factor the maximum vertical resolution is .7 of the number of horizontal scanning lines. Using this the maximum vertical resolution is
PAL 625 X .75 = 470 lines
NTSC 525 X .7 = 393 lines
Vertical resolution is not critical as most camera manufacturers achieve this figure.
Horizontal resolution = no. of vertical lines
Theoretically horizontal resolution can be increased infinitely, but the following two factors limit this
It may not be technological possible to increase the number of pixles in a chip.
As the number of pixels increase in the chip, the pixel size reduces which affects the sensitivity. There is a trade off between resolution and sensitivity.
If only one resolution is shown in the data sheet, it usually is the horizontal resolution.
Measuring the Resolution
There are different methods to measure resolution:
1. Resolution Chart
The camera is focused on a resolution chart and the vertical lines and horizontal lines are measured on the monitor. The resolution measurement is the point were the lines start merging and they can not be separated.
- The merging point can be subjective as different people perceive it differently
- The resolution of the monitor must be higher than the camera. This is not a problem with Black and white monitors, but is a problem with most color monitors as they usually have a lower resolution as compared with a camera.
This is a scientific method to measure the resolution. The bandwidth of the video signal from the camera is measured on a oscilloscope. Multiply this bandwidth by 80 to give the resolution of the camera.
Eample. If the bandwidth is 5Mhz, the camera resolution will be 5 * 80 = 400 lines
Monocrome Cameras (or night/day during night)
Color Cameras (or night/day during day)
380 - 420 Lines
470 - 600 Lines
470 - 540 Lines
|High Definition 1.3 Megapixel (IP)||960 Lines (only possible with IP Cameras!)||960 Lines|
|High Definition 3.1 Megapixel (IP)||1536 Lines (only possible with IP Cameras!)||1536 Lines|
As you can clearly see in the table above; only IP Cameras are able to enter into the HD High Definition CCTV Resolution range. Analog CCTV Cameras have reached the end of their thread. The signals transmitted via coaxial cables cannot carry any more information. The 'Great Exodus' from analog to IP will begin between now and the next couple of years, as increase of identification chances, camera intelligence and installation cost reductions are moving into the foreground.
Ideal CCTV recommends to seriously consider IP based solutions for complete new installations. This will ensure a future proofed investment and compliance with future industry and government standards.