What is Dynamic Range?
Dynamic range is the ratio of the maximum signal output of the sensor to the smallest signal output of the sensor. Or, in other words, dynamic range is the ratio of the brightest portion (maximum output) of the image to the darkest portion (smallest output) of the image.
Most standard CCD sensors have a contrast ratio of 1:1000 (60dB) while wide dynamic range sensors have a contrast ratio of 1:1800 – 1:5600 (65-75 dB). So, the wider the dynamic range, the better the sensor can accurately capture varying light intensities and heighten the details visible within an area.
Why is it important?
Having the correct amount of light is vital for capturing useful footage from your video security camera, but light cast in the wrong direction can also render a camera useless. Lighting should be orientated towards the subject of your video and not towards the security camera.
Unfortunately, that’s not always possible. Video security applications often require placing security cameras in areas with difficult lighting conditions. Examples include:
- Where the subject is positioned against strong back lighting such as a heavily windowed storefront
- Areas where there are abrupt changes in illumination like an entryway
- Where the lighting conditions are reversed, such as looking from a well-lit area into a darker area
Standard security cameras adjust to the brightest source in the image, making details in the darker areas of the image hard to distinguish. To combat this, Wide Dynamic Range (WDR) video security cameras are employed in situations where there are varying lighting situations. WDR enables the camera to deliver video with near perfect exposure in the harshest of lighting conditions.
Obtaining Wide Dynamic Range
There are two basic solutions that are used in WDR video security cameras:
- Multi-frame imaging – the camera captures multiple versions of the field-of-view with each version at a different contrast ratio. The camera combines the frames to eliminate the darkest and brightest portions of the field-of-view producing the WDR frame.
- Non-linear sensors – these are usually logarithmic sensors on the imager that are triggered based on different illumination levels within the viewable area. Non-linear sensors differ because they allow the capture of a WDR image all in one frame.
Of the two solutions, multi-frame imaging is the most widely used for wide dynamic range because it is more suitable for capturing images in real time and can process moving objects more quickly.