WDR, D-WDR and the Future of Light Compensation

If you've ever taken a photo in sunlight from your smartphone or placed an older model CCTV camera outside in a position where it is exposed to varying degrees of brightness, the chances are that at one point in time you may have experienced loss of detail in the darker areas of the picture. You may also have noticed that in some conditions you can also lose definition in the brighter parts of the picture too leading to what is mostly an ineffective and unusable picture quality.

This is one of the most common problems found whilst installing CCTV, and in the past heavy light sources would lead to some installers totally re-positioning cameras. The loss of picture quality occurs due to the difference between the brightest areas and the darkest. This difference in brightness is called 'dynamic range' and sometimes the difference can be so great your camera struggles to find an exposure that can capture both of them at the same time leading to loss of image.

There are a few technical methods that a camera can use to adjust light levels, these are:

Backlight Compensation (BLC)

Backlight compensation is a mechanism where a camera can compensate for backlight by improving its auto exposure. Backlight compensation ignores areas of high illumination but ensures that most of the picture  still remains bright. An example of a situation that requires. BLC is where you have a subject with window behind them with sunlight beaming through, this causes shadow on the subject.  BLC will compensate to get rid of the brightness whilst ensuring the room is still bright enough to capture the subject. Although BLC is still currently used in some cameras it is less favoured over WDR technology.

Wide Dynamic Range (WDR)

Many cameras today capture a wide dynamic range (WDR) of brightness values this allows them to essentially deal with varying incoming light sources and automatically adjust the cameras sensor to maintain the brightness, contrast and exposure of a scene. This helps to produce a clear, and more importantly for security cameras useful CCTV picture. A cameras capability of dealing with these changing light sources vary, every camera has its limits. A cameras WDR is measured in DB, so for example a camera with a high WDR would have around 120DB.

BLC and WDR sample

Digital Wide Dynamic Range (D-WDR)

Digital WDR (D-WDR) is a software-based technique that optimizes image quality by adjusting the gamma (γ) value to enhance dark areas. With the D-WDR camera, the image is processed through the digital signal processor instead of the image sensor, which allows for greater flexibility with settings. With a D-WDR function on your camera you are usually given a range of exposure options to initially choose from and adjust according to the light conditions of the area being recorded. For ease these options are usually numerical and selecting the right preferences will help to minimise image depreciation.

High Dynamic Range and the Future of WDR

One of the best mechanisms in the world to use WDR is the human eye. Our eyes are constantly adjusting to adapt to changes in light and it was once the goal of image sensor manufacturers to produce a technology that was similar to this. High Dynamic Range (HDR) has been developed as a technique that is similar to the human eye and reproduces a greater dynamic range of luminosity compared to current D-WDR sensors. HDR can cope with extreme lighting conditions such as extreme shade and direct sunlight. HDR technology can currently be found in CMOS sensors and the most recent model of the iPhone (check out our range of cameras with CMOS).

However the problem with HDR is not taking the image which is fairly straightforward, the problem is processing the data and rendering it. CMOS sensors can capture high dynamic range images however with current technology this image is compressed to a smaller dynamic range when processed this process has various names such as true WDR, real WDR and life WDR. Although these images which are produced through a CMOS sensor are regarded as better than digital wide dynamic range, it is now the goal of manufacturers to produce cameras that can fully process the data that comes from a CMOS sensor.

Further to this, the development of HDR lenses will also help to improve on the intensity of various wavelengths of light coming through resulting in an even higher dynamic range image. Such lenses are currently being trialled on the international space station for capturing images of the universe.

Take a look at our range of cameras with WDR >>