Tuesday, January 3, 2017

What is WDR in Surveillance Cameras?

WDR stands for Wide Dynamic Range, and is essentially the ability to produce high quality image across a wide range of light levels. For example, the center of an image or scene may be very bright due to the sunlight behind a person entering a doorway (or standing in front of a window), while the areas on either side of the entrance (window) are much darker. In CCTV Cameras without WDR, the person may appear as a shadow with no discernable features. Cameras with WDR will compensate for the variance in light levels to allow a more detailed image across the entire frame. The camera will even showing facial features, hairstyle, etc. while still giving details of the darker areas as well.

WDR can make a big difference in scenes with widely different light levels. The WDR feature in CCTV Cameras can maintain proper image brightness, exposure, and contrast to ensure image clarity. Both analog, HD analog and digital IP cameras offer this function. DB is the value to measure the wide dynamic range in a given surveillance camera. A higher WDR range (for example 120DB), represents camera can catch a greater scale of brightness.

Understanding wide dynamic range (WDR) in CCTV Cameras is critical to capturing high quality images in demanding lighting conditions. However, with no real standards, any manufacturer can claim WDR, and many do even if actual performance is weak, causing confusion for even experienced surveillance camera installers. Digital WDR is a feature on many cameras but is not ‘True’ WDR which is much more effective.

Digital WDR (D-WDR) is a software-based technique in CCTV Cameras. DWDR optimizes image quality by adjusting the gamma (γ) value to enhance dark areas. The Camera D-WDR level, should be carefully adjusted according to the lighting conditions in order to minimize possible image deterioration (i.e. the image being washed out).

True WDR is a sensor-based technology. CCTV Cameras with this technology can produce images with an extremely wide dynamic range. The WDR image sensor can capture several images with short and long exposures, then combining them into a single frame. Generally, True WDR can be adjusted using three pre-set levels (Low/Mid/High) according to the lighting conditions. Proper calibration of WDR level is essential to achieving the best result –setting the WDR level too low may not produce satisfying visibility, while setting the WDR level to high may lead to washed out images. Regardless, True WDR is the more effective technology in Surveillance Camera applications.

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