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What is WDR?

What is WDR?

A dynamic range is the the ratio between the largest and smallest measurable quantities of something. In the case of video surveillance, the dynamic range is the ratio between the lightest and darkest elements of the image. WDR (Wide Dynamic Range) technology is great for high contrast scenes, which balances the brightness and shaded areas simultaneously so that an image doesn’t appear blown out or too dark.

Decibels (dB) are the value in which dynamic range is measured. IHS defines WDR at 60 dB or greater, though it’s not uncommon to see WDR cameras with capabilities of 120 dB or more. While comparing product datasheets, it is possible that a camera with a lower ratio outperforms a competitor with a higher dB ratio.

How it works

Security cameras with WDR technology use either Digital WDR (DWDR) or True WDR. True WDR uses image sensors and a digital signal processor (DSP) in order to provide even illumination to all areas of an image. True WDR-enabled video surveillance cameras have two sensors which take two scans of each video frame. The first, at low speed in order to capture more light, shows the image in normal light conditions. The second scan is taken at high speed to capture less light overall and get an image with strong light in the background. The DSP combines the two scans to form a single, balanced, well-illuminated image.

DWDR uses algorithms instead of sensors in order to digitally brighten areas which are too dark and dim areas that are too bright. DWDR relies on the DSP chip instead of the image sensor to provide WDR, which adjusts each individual pixel of the image and calculates the exposure. This technique has some limitations, as the intense manipulation of pixels leads to the overall image being more grainy. DWDR however doesn’t need costly image sensors, so it can be a more economical option when WDR is a necessity.

There are two options for improving the exposure of an image without using WDR. For example, in a high-contrast scene with heavy, broad, backlighting the cameras would adjust to the average illumination which would darken the image. If there is no WDR available a Backlight Compensation (BLC) would brighten the image so that you could see darker details better. Backlight Compensation is a legacy technique which uses a DSP to increase the level of exposure for the entire image. DSP’s are used to brighten the entire image, which is a good solution to prevent washing out images which are already overly lit.

Highlight Compensation (HLC) is a technology where image sensors detect strong light within the image and reduce exposure on those areas in order to enhance image quality.  If an area is dimly lit for example this may be caused by a hot spot such as headlights or street lights, the overall image may become too dark, therefore if there is no WDR available you should use a HLC. The camera would automatically suppress bright light sources and allow proper exposure of the adjacent areas.


Regardless of dB value specified, image results will vary depending on the complexity and amount of movement in a specific area. In order to determine the best camera for an application, it is always important to test it to make sure that it meets the needs and expectations of the customer.

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