Making light of poor lighting

March 2009 CCTV, Surveillance & Remote Monitoring

Jacques Botha, manager of Norbain SA’s technical division throws some light on WDR technology.

WDR (wide dynamic range) technology was developed for use on imaging devices ie, cameras. It is related to BLC (backlight compensation) and its primary area of address or concern is the efficient reproduction of highlights and shadows as encountered in many images.

We often find these stark contrasts alongside one another in a single image and while BLC was initially developed to combat image washout or similar problems it is more often than not insufficient.

A real life example would be a camera facing a door that leads out of a dark hallway to the outside of a building (in other words, plenty of light, and as it is outside, expect sunlight). If we place an object in front of this closed door we may find that (assuming the camera specification is sufficient and the device was setup correctly) the camera will be able to reproduce images where a user can discern individual features such as buttons on a shirt and facial features, to name but two. This is the status quo as long as the door remains closed and lighting conditions are unchanged.

In the next instance we assume that the door opens and a person enters the hallway. The door is still open behind this person and there is a lot of bright light entering the hallway from behind our subject.

The camera (akin to the performance of the human eye) now has too much light to contend with and reproduces images that appear overly bright or washed out. Detail such as facial features and the aforementioned buttons are now mostly in the dark with this object (the person) being back lit.

The camera now needs to reproduce this as true as possible and due to dark and bright areas, struggle to find a median. The result is a very bright doorframe and a shadowy figure approaching the camera through it. No detail, or very little is discernable.

Enter WDR. The camera will use a technology such as APS (active pixel system) to accentuate the differences between individual pixels (picture elements) and detail can be seen again despite the fact that it is not the part of the object bathed in light.

The Samsung Techwin SHC-735P employs digital pixel system and active pixel system type technologies known to CCTV users as WDR. This ensures the ability of the image sensor to quantify and subsequently represent highlights and shadows in the same image. The end result then, quite simply, is a camera with better video reproduction under such adverse conditions as stated above.



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