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Choosing the Right Surveillance Camera

23 May 2016

Making Sense of Sensors

Every day over 566 petabytes of data is generated by surveillance cameras. Predicted growth in the global security market is such that this figure is expected to quadruple in just three years. It’s clear that global demand for cameras is high.

Often less clear, however, are the intricacies involved in selecting the right camera for the right application. Small details, either relating to the technology itself or the environment in which the camera operates, can make a big difference to performance.

In this Interview Room - the first in a series of camera specification specials - we talk to Wayne Barraclough, Synectics’ Product Manager about the importance of sensors, particularly for organisations considering an HD upgrade.

What is the role of a sensor exactly?

The role of a sensor is to capture light entering through the lens in order to form an image. Every camera has a sensor. On each sensor are a specific number of pixels which each contain a light sensitive element that detects photon levels. When hit by light, each pixel on the sensor generates a charge which is then amplified and converted to a digital signal. The combination of signals from all the pixels enables the image to be created.

So why does this matter so much in terms of camera specification?

The biggest implications are in terms of pixel count. Imagine that you have two cameras operating under the same conditions. Both sensors have a 2MP pixel count but one sensor is physically bigger. Which camera will produce clearer images? The answer is the camera with the physically larger sensor. Why? Because the pixels are larger/less densely packed and therefore have greater capacity to gather light.

However, the majority of camera sensors for commercial or industrial use (i.e. non consumer markets) are a standard size (1/3-inch) which means that as pixel count increases in the pursuit of higher definition images, pixel size has to decrease. This is why, for example, an HD 2MP camera can outperform a 3MP camera (assuming both have the same size sensor).

To summarize, the best image is not delivered by more pixels, it is delivered by having the right number of pixels relative to the size of sensor. Generally speaking, the bigger pixels can physically be, the clearer the image will be, especially in lower lighting conditions.

Won’t sensors advance to be able to accommodate higher pixel counts?

They will. In fact a lot of R&D has focused on the development of ‘micro pixels’ (pixels less than 3um) that have stronger low light performance despite their diminutive size. This does mean that denser pixel counts are now possible on 1/3-inch image sensors without such a dramatic impact on image quality but there is an associated price tag. This type of technology isn’t necessarily available as standard so organisations need to be aware of the potential issues and ask about sensor capabilities in this respect.

Are there any other important considerations in terms of camera sensors?

Yes, having the right lens is a big consideration. It is vitally important that lens and sensor are compatible in terms of performance – a mismatch can result in significant quality loss (in many cases negating the perceived benefit of an HD camera upgrade). With any camera, the lens should equal or exceed sensor performance in order to maximize camera capability.

Aspect ratio is another consideration in relation to sensors – why is that?

This is something I have touched on before in an article “Specifying Surveillance” for PSI Magazine here. Image aspect ratio is primarily determined by the camera sensor and many sensors currently in use capture images with a non-standard aspect ratio (eg 3MP sensors are typically 2048 x 1536 which is 4:3). The problem is that most display monitors, in line with the HD revolution, are 16:9. This typically results in one of two outcomes. Either the image is altered to fit the display setting (the outcome of this being image distortion), or the image is cropped to fit and appears with black borders. Neither scenario is desirable in settings where whole scene awareness and image detail are a priority.

The third option is that settings are adjusted to display correctly in the 16:9 format by setting the resolution to 1080. The net result is often that, due to pixel size/density, the picture is of inferior quality than when using a 2MP sensor.

What about 4K cameras, aren’t they 16:9 compatible?

They are. With a pixel density (8MP) four times greater than standard HD, larger sensors and a native 16:9 aspect ratio, 4K cameras have a lot going for them. Sensor technology will develop further alongside 4K I’m sure. But even now, though light sensitivity may diminish slightly, the image is so good that any payoff is worth it. However, price point, storage and network compatibility challenges mean that we have a way to go until 4K is a realistic option for the majority of large scale surveillance settings.


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