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

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

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.

Problems

• 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.

Bandwidth method

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

Typical Resolutions of Cameras

	Monocrome Cameras (or night/day during night)	Color Cameras (or night/day during day)
Low Resulation	380 - 420 Lines	330 Lines
High Resolution	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.