CCTV – Let there be light – Part 1 Infra-red

Like the human eye, a camera cannot capture images without light. When it comes to CCTV cameras, with moving images, the quality of the camera and the type of light will determine how good those images are.

A cheaper camera may have several compromises, for instance the lens and the charge couple device (ccd – this is what converts the image into electronic signals) may only produce a low resolution image. You will see this as poor definition and grainy images, especially when they are enlarged. How many times have you looked at CCTV images on TV and thought how poor they are?

At night with low light levels, a camera will usually switch to black and white and infra-red IR radiation.

This is for two important reasons:

1)                          Black and white images require less light, we also see in black and white when the light is very low, try wandering around at night in almost total darkness.

2)                          Infra-red radiation is just outside of the visible spectrum but it transmits the heat reflected from objects, which in an infra-red camera can be converted to a visible image.

This extra detail can be added to the visible light component to enhance the overall image being viewed, which is very valuable technique, but it does have it’s drawbacks.

In cheaper cameras the switch to infra-red at night is purely electronic. This tries to adjust the difference between the two settings using only electronic manipulation. The problem with this approach is that the actual wavelengths of the IR and visible images are different. This difference cannot be adjusted electronically, so you lose both definition and colour balance. More expensive cameras have a mechanical IR cut filter which is automatically withdrawn at night. This allows more light to enter the camera and corrects the focal length for Infra-red radiation. During the day when there is plenty of light, the filter is in place. The infra-red radiation is filtered out which allows the camera lens to accurately focus on the visible light providing sharper images that are also more accurate and richer in their colour.

At GuardHome we only use IR cameras which include an IR cut filter so that our systems deliver the most accurate images to aid in recognition and definition.