The Wide Dynamic Range (WDR) function of a camera is intended to provide clear images even under back light circumstances where intensity of illumination can vary excessively. The WDR allows a camera to filter the intense back light surrounding a subject and thus enhances the ability to distinguish features and shapes on the subject. WDR cameras are usually recommended for situations where light enters a premise from various angles such as a multi-window room. A camera placed on the inside of the room will be able to see through the intense sunlight or artificial light coming in.
If an indoor security camera is pointed towards a window or an entrance door, you will see the background washed out during daytime. This is very common situation in restaurants and stores which have big glass windows.
To fix this problem, cctv manufacturers came out with WDR (Wide Dynamic Range) technology.
The way it works, a camera is fitted with two CCDs. One high speed CCD and one low speed. The two CCDs take 2 scans of the same image instead of one scan like a typical camera.
The first CCD scans the images in normal light condition. After that, the camera scans the second time at high speed to get the image with strong light background. The image processor then combines the two images into one to provide a balanced image which shows the indoors and outdoors clearly.