“Megapixel camera” – a misleading concept
Yes, I know. We live in the HD era. Everybody speaks HD. HD video, HD movie, HD camcorder. And, unsurprisingly, everybody talks about megapixels. Actually, a whole industry has been built around the term ‘megapixel’.
But what is behind the whole thing? Does HD mean better quality? And: how many megapixels is enough – especially in CCTV? Let’s see it for ourselves, shall we?
Pixels – what are they?
Pixels are ‘picture elements’. Pixels build up a digital picture. In some formats these pixels are square while in other formats they are rectangular. Let’s see a couple of examples:
In Europe, before the HD standard swept over the continent, a standard called PAL was used in the video industry. The standard set the aspect ratio to 4:3. Moreover, this standard also determines the number of pixels within the picture: 720 pixel horizontally and 576 pixels vertically.
If you make a simple calculation, you will find out that these pixels are not square but rectangular ones – standing on their shorter sides.
Let’s examine HD now: full HD sets the aspect ratio to 16:9 (widescreen) and the number of pixels to 1920 pixels horizontally and 1080 pixels vertically. This dimension determines that pixels are square.
However, in every area the number of pixels varies. There is one thing though, that is determined and it is the picture aspect ratio i.e. 16:9.
So, why is the number of pixels so important?
Number of pixels – they determine… what do they determine?
To put it simply, the number of pixels determines the details of a pictures. In other words, the more pixels you have in a square inch, the more details you can record. Why is it a great plus?
It can be a great plus in certain situations. Imagine a CCTV camera in a public garage. These cameras have to survey the area and detect number plates – which means zooming is required.
You can choose to zoom optically which is not only expensive but sometimes slow or even inaccurate. The other way is zooming digitally right into the footage. Now, this is when the number of pixels determines the end result i.e. having usable or crappy images.
Digital zooming means that you magnify the pixels. The more pixels you have, the smaller they are and will remain small enough until a certain amount of magnification, which results in a decent picture quality.
How about field of view?
This is a concept that really drives people nuts. For an end user, HD simply means widescreen. And wider screen means wider field of view, right? Dead wrong.
Theoretically, if we put two almost identical cameras next to each other and the only difference between them is the aspect ratio, we can say that, the widescreen covers a wider area. True, but it is not a realistic situation.
The field of view can be altered in many ways. Eg. using wide angle lenses you can widen the field of view drastically. Or, a smaller sensor results in a bigger crop-factor compared to a bigger sensor.
Then the question arises:
What really makes a camera produce clear footages?
There are numerous factors you have to take into consideration:
- the lens
- the amount of light available
- the size of the sensor
- the number of pixels
- the frame rate
- the bitrate
You can read a full article about them here: what determines the picture quality in CCTV image recording?
Any drawbacks resulting from the high number of pixels?
Disappointingly, yes, there is one. There is a tendency in the industry. We call it pixel stuffing. It means that manufacturers try to stuff more and more pixels into their small sensors. It has its drawbacks when it comes to low light.
In low light conditions pixels create noise. A lot of noise. So, if you operate a CCTV in low light, what you need is a bigger sensor – not even more pixels!
When you next go to your local CCTV shop…
- Don’t automatically go after the megapixels
- Know what you need your CCTV camera for
- Know that widescreen does not automatically means wide field of view
- Keep in mind that in low light conditions you need a camera with a big sensor
- Remind yourself that you definitely need a higher number of pixels if you need to zoom into your footage during or after the recording
Yes, we live in the time of HD and there is nothing wrong with it. Just don’t let the marketing hype drift you away. Right?