BLOG – Multi-megapixels in security cameras: not the be-all and end-all
By: Jan van Essen
Multi-megapixels in security cameras.
That should make for great images.
Or is it?
In this blog, I’ll explain what role pixels play and what other factors determine the quality of a camera image. Many people think that the more megapixels there are on the chip in the camera, the more detail and the better the image.
That’s only partly true.
Depending on the situation and the intended purpose, there are also other factors that come into play.
Since the introduction of digital (security) cameras , the number of megapixels on the image sensor has increased enormously.
From a million to 10 to 12 million pixels.
The size of the image sensor, on the other hand, has not changed (almost).
You can’t, because there’s no room for that in today’s compact security cameras.
We started placing more pixels on the same surface, so the pixels themselves became smaller.
And here’s the rub. It seems that the smaller pixels can convert less light into an electrical signal, making them less suitable for dark situations. Security cameras intended for identification not only need to see a lot of details, but also ask for high light sensitivity in dark situations. After all, most security risks are at night.
The number of megapixels on the camera chip only partly determines the quality of the camera images.
Lens quality and size
Image quality is also determined by the quality and size of the lens used.
In order to properly project image information onto the chip, a lens is needed that brings the light together on the chip from a certain aperture angle.
The lens must also allow as much light as possible to pass through to the chip.
You do this by using pure glass (which also prevents distortion) and making the lens as large as possible.
Telephoto lenses on professional photo cameras have a lens the size of a cake dish for a reason.
Unfortunately, such a lens size is not realistic on a security camera.
You can see the limitation of the smaller lens when you digitally enlarge the image: it becomes blurry rather than looking at a blocky image as with a low resolution.
With more pixels, we can keep more detail with larger aperture angles, but the limitations of the lens will then play a major role.
A fisheye camera, for example, has a lens that projects the full 360 degrees of the situation onto the chip.
Ideal for identification in smaller spaces such as entrances, stairwells and elevators.
If this camera is used in larger spaces such as parking garages and halls, you can only distinguish between a human or a dog at a greater distance.
Identification is no longer possible at that great distance.
At the moment, there are already 12 Megapixel fisheye cameras for sale, but they have a small lens with thick glass.
And that’s a limitation.
If you want to take identifiable camera images in these kinds of large spaces, it is better to choose a multi-sensor camera.
These are multi-megapixel camera modules with smaller aperture angles in one housing, which transmits the images from the different modules as a single image.
How many megapixels do you actually need?
Some camera manufacturers are actively participating in the multi-megapixel hype and offer 4K (8-megapixel) or even 8K cameras.
They come with a hefty price tag and the sensitivity in the dark often leaves something to be desired.
How many megapixels do you really need?
An 8 megapixel image gives, on a normal screen, the maximum detail we can see with our eyes.
Of course, we can still zoom in digitally, but even then you run into the optical limitations of the lens.
With a fixed camera, you have a lot of details, but in most situations there is no need to count the nose hairs of the person in the back of the store.
In addition, the camera cannot see around corners.
Multiple cameras with, for example, 3 megapixels (which are more light-sensitive) provide better image coverage and give a greater chance that the (un)desired situation is in the picture.
With a controllable camera, you can already bring out the image optically and multi-megapixel is of secondary importance.
It is nice to zoom in digitally in the overview image afterwards, but because of the lens package, a multi-zoom camera does not provide as good images.
Finally, all those megapixels also create large files and streams that need to be sent and stored over the network.
This disadvantage can be somewhat eliminated by applying image compression methods such as H.265.
Conclusion
When choosing suitable cameras, look beyond the number of (multi-) megapixels.
Above all, let your choice be determined by the intended purpose.
Multi-megapixel cameras are useful for large overview situations such as football stadiums, squares and fields.
But in almost all situations, the right camera projection is finding a balance between need (e.g. purpose and lighting conditions) and price, and multi-megapixels are certainly not the be-all and end-all.