Mega Pixel – a technical view

The CCTV industry is pushing Mega Pixel (MP) High Definition (HD) as the big thing in cameras but is it really replacing the analogue camera.

The following takes a technical view at some of the prose and cons based the comparison of a 35X analogue PTZ compared to a fixed position 5MP camera looking across a typical sports stadium.

Effective resolution of digital zoom

My research has highlighted to me that digital zoom of a mega-pixel camera also has the inverse square law applied.

This means that for every 2X zoom, you divide the pixel count by 4. for 3X zoom, by 9. And the killer, an 8X zoom is divided by 64. Therefore if you have a  5MP camera at each zoom step, you will end up with the following effective pixel count.

Digital Zoom 0X 2X 4X 6X 8X
Pixels H x V 2592 x 1944 1296 x 972 648 x 486 432 x 324 324 x 243
Relative MP Size 5MP 1.2MP 0.32MP 0.14MP 0.08MP
Equivalent lens 16mm 32mm 64mm 96mm 128mm
    Near 720P HD Same as VGA   Same as CIF


Using a CCTV 3D drawing software, this gives the following results based on the following cameras and zoom ratios

5MP ½” with 16mm lens set to full resolution 35X PTZ set to 4CIF

0X digital zoom

10X optical zoom

4X digital zoom

15X optical zoom

8X digital zoom

35X optical zoom


5MP security camera resolution at 8X zoom5MP ½” with 16mm lens 8X digital zoom resolution





35X IP PTZ security camera resolution at 35X optical zoom35X PTZ set to 4CIF 35X optical zoom resolution



5MP ½” with 16mm lens 0X digital zoom


5MP security camera at 0X digital zoom

35X PTZ set to 4CIF 10X optical zoom


35X IP PTZ security camera resolution at 10X optical zoom


5MP ½” with 16mm lens 4X digital zoom


5MP security camera at 4X digital zoom

35X PTZ set to 4CIF 15X optical zoom


35X IP PTZ security camera resolution at 15X optical zoom


5MP ½” with 16mm lens 6X digital zoom


5MP security camera at 6X digital zoom

35X PTZ set to 4CIF 30X optical zoom


35X IP PTZ security camera resolution at 30X optical zoom


The inverse square law applies to lighting in CCTV, which states that every time you double the distance from the camera to the object of interest, the light reaching the camera is reduced to ¼.

This means for a camera looking across the oval some 170+ metres, the lux level required on the person is going to need to be very bright. Looking are night time games on television, the rear 2/3rd rows of seating are quite dark. I do not know what the actual lux level is and this may be worth looking into prior to installing the cameras.



As illustrated, the results of a 5MP compared to a 35X PTZ are very much in favour of the PTZ.

The effective resolution of a 8X digital zoom is CIF and the PTZ can produce the same level of zoom at 4CIF.

Based on these results, I would recommend either install 3 or 4 PTZ cameras, which will give improved angles of view and not suffer from as much sun glare in the evening matches from at least 2 of the cameras.

However once HD PTZ cameras become a common product, this will give the advantage on the analogue PTZ plus the resolution of the MP camera.

Example angles of view using 3 35X PTZ cameras



Example angles of view using 3 35X PTZ cameras showing the same person from different angles


Tags: , ,

Leave a Reply