Guest Column | December 3, 2013

WDR Is Everywhere Lately, But What Is Wide Dynamic Range?

By Wendi Burke, Director of Marketing, IQinVision

The term Wide Dynamic Range (WDR) is used to describe the function of a camera designed to produce clearer, more actionable images and/or video in circumstances where back light and intense illumination can vary excessively, especially when both very bright and very dark areas are simultaneously present in the camera’s field-of-view. The wider the dynamic range, the better the camera’s sensor can accurately capture varying light intensities and then heighten the details visible within the area of view.

Examples where WDR functionality is most needed include:

  • Instances where the subject is positioned against strong back lighting, such as a heavily windowed retail storefront or office
  • Areas with rapid and constant changes in illumination, like entryway/exit points
  • Where the lighting condition in the field-of-view moves from a well-lit area into a darker area
  • City transportation centers such as parking garages, tunnels or train stations, where people and vehicles enter and exit (commonly with bright daylight outside and low levels of light inside)
  • Scenarios such as toll plazas, gas stations, and anywhere vehicles with bright headlights are driving directly towards the camera
  • Environments with intense light reflection off banks of windows such as with office buildings and shopping malls, or for areas with water features

The challenge in attaining consistently high-quality surveillance video is that the camera needs light to generate an image. But too much light and the image is blown out; too little light and the image is dark and unusable. Often, a scene has a wide range of light variation and the camera simply can’t adjust its iris settings or shutter speed to properly adjust for the optimal amount of light. Hence, WDR techniques have been developed to improve the speed of iris adjustment and thus enhance video quality and integrity.

WDR Techniques

There are two basic techniques commonly used to successfully provide WDR capability:

  • Multi-frame imaging. In this technique the camera captures multiple frames of the field-of-view; each frame having a different dynamic range. The camera then combines the frames to produce one improved WDR frame (see example below).
  • Non-linear sensors. These are typically logarithmic sensors, where the sensitivity of the sensor at different illumination levels varies, enabling the capture of a wide dynamic range image in a single frame.

Of the two techniques, multi-frame imaging is the most commonly used by manufacturers supporting WDR capability for two main reasons. First, it is superior at capturing images in real-time, and secondly, it can process moving objects more quickly than non-linear sensors. Multi-frame imaging is also more cost effective and integration friendly because it is far more common in the marketplace. While non-linear sensors do perform well, they have not been widely adopted and current trends do not suggest this technique will overtake multi-frame imaging in popularity in the near future.

This article first appeared on IQinVision’s site. To read the article — which includes examples of photos taken with and without WDR, as well as tips for its use — click here