HD Video Surveillance
light performance is governed by processing. It was mentioned earlier that Benchmark’s assessments of various cameras using a uniform sensitivity test showed little advances in recent years with all processing disabled! It matters not how good a camera’s
processing is; even very good processing will be disadvantaged if the original image is affected by low light. The second - and arguably more significant -
reason that HD cameras have inferior low light performance has to do with pixel size. Image sensors require light to fall onto the pixels to create the relative values that make up the image. If you consider a 4CIF camera chip, it contains around 400,000 pixels. In effect, this means that the surface of the chip is divided up into 400,000 picture elements onto which enough light must fall to create a strong signal, every time a frame of video is created. The size of the picture elements affects the
low light capabilities of the camera, which is why 1/2 inch CCDs are better performers in low light than 1/3 inch CCDs! With this in mind, consider that a HD
camera has around two million picture elements on the same size chip as the 4CIF camera. Because the pixels are so much smaller, the low light performance is bound to be inferior. However, resolution is greatly increased!
An illuminating thought
The fact that HD video cameras do not match analogue cameras with regard to low light performance must be put into context: analogue cameras also struggle once light levels fall below a certain point. The need for additional illumination is not an HD issue. Illuminators were around for many years before HD cameras ever were! One thing to remember is that a HD image
has around four times the definition of a standard camera, which means that any issues with lighting - hotspots, fade, uneven coverage or any other aberrations - will be much clearer in the final image. As with lenses and housings, there is little point in making something to a higher quality
than is required. It only adds to the overall cost. Therefore, many manufacturers produce illuminators that work perfectly well with standard cameras, and any issues don’t show up because the camera simply isn’t affected by them. A HD camera, however, will be. To test this, Benchmark set up an
unbranded low cost infrared illuminator and a white floodlight from a trade outlet, alongside an infrared PoE infrared illuminator and a white light LED illuminator from specialist manufacturer Iluminar. With a standard definition camera, both IR illuminators seemed fine, with the unbranded unit showing some fade towards the edges of the field of view. The white light illuminators were slightly more different, with the Iluminar unit producing a clean consistent coverage of light, while the floodlight showed pooling and slight colour anomalies. Switching to a HD camera using a megapixel lens, the difference in the units was amplified. The unbranded infrared unit was clearly delivering an uneven coverage, to the point that the usable range would be limited unless you really knew what you were looking at. The Iluminar infrared unit and the Iluminar white light both continued to give consistent and even coverage. The unbranded floodlight was, quite frankly, horrible. Light quality with HD is important, because
differences will be much more obvious. There is a secondary issue too, which is true of all cameras. Additional light creates clean and noise-free images, which allows compression to work better, thereby reducing storage requirements. Some might also point out that it can reduce bandwidth. However, this is a moot point, as most systems will use constant bitrates. The image, however, will certainly be cleaner.
In summary
Just as it makes little sense to use HD cameras without megapixel lenses or housings with quality window materials, it is equally important to ensure that the cameras are supported by high quality illuminators if you are to realise the best image quality!
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