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Dynamic range is the difference in brightness between the darkest and lightest part of an image. In order to capture an image with a wide dynamic range, conventional video cameras employ a variety of processing techniques. However, even the best camera will eventually struggle to cope with extreme changes in brightness. In fact, the best surveillance tool in the world for coping with a wide dynamic range is the human eye – it can adjust faster to sudden changes in lighting than any conventional camera could hope to achieve.
Modern still-image cameras take a number of images in quick succession at different exposures. These can then be processed together by the camera or edited together on a computer to create a balanced image. This High Dynamic Range (HDR) technology is relatively easy to employ in a still-image camera, as only a single static image needs to be composited. The real challenge comes with attempting to perform this multiple exposure compositing function 30 times a second to create HDR video.
IP video surveillance Camera manufacturers use a variety of image optimisation tools to improve dynamic range. A camera that employed HDR video technology would be like looking through the human eye which is able to cope with even the harshest changes in lighting. A conventional IP security camera has to compensate for sudden changes in lighting, such as a door opening, or a light being switched on and off. A HDR video camera would simply see the door opening, or the light being switched on and off, without the rest of the picture being affected. Such technology makes it much easier to track people and objects, identify faces and maintain a solid, reliable surveillance presence in the most difficult lighting conditions.
WDR refers to a camera’s ability to produce high-quality images across a wide range of light levels. An HDR camera can better illuminate darker parts of a scene without overexposing lighter areas. It also won’t create noise or distort image quality, which can occasionally happen with some digital WDR cameras.
The images below show that an HDR camera outperforms a camera with digital WDR by providing more detail in both the darkest and brightest areas of the scene.
HDR needs greater processing power HDR extends the dynamic range of a camera by taking two separate frames – one with a short exposure and one with a long exposure – and combining them in real-time into one image with the best balance of lighting possible. Essentially, HDR merges the highest-quality parts of two exposures into one image.
Camera with no WDRCamera with HDRCamera with WDR
An HDR camera therefore needs a lot of processing power, and a very powerful sensor, capable of producing 60 frames per second (fps), or double that of a regular IP camera.
HDR is used in still photography, but is relatively new to the video surveillance industry, where features like digital Wide Dynamic Range (WDR) are more common.
Using traditional capturing and compression techniques, a HDR video camera would require 48 GB of storage space for every minute of video captured. The largest commercially available hard drive could store less than an hour of HDR video. Researchers are working towards reducing these requirements by a factor of 100 through the development of new software.
Applications
High Dynamic Range is desirable in nearly every IP surveillance application, from the home user to corporate deployment. With big advances already made in video quality and compression for IP cameras, HDR could be the element that turns excellent images into truly exceptional ones.
Properly illuminating a highly contrasted image is possible with a camera that uses High Dynamic Range (HDR). HDR cameras are ideal for security applications because they provide investigators with higher quality video evidence. Important details, such as aspects of clothing or facial features, are easier to identify.
Banks in particular can benefit from HDR cameras because they often have large customer lobbies with lots of window space exposed to direct sunlight. Ideally, pinhole or ATM cameras should also offer HDR because the angle and field of view they capture typically involve bright light in the background.
Mr. Kiron Kunte
About Author
Kiron Kunte has over 35 years of design and solutions experience, in Security, Telephony and Networking infrastructure. He is a graduate of IIT Bombay, a Fellow of the Institute of Engineers and has a post-graduate diploma, from Bombay University, in Systems Management. He is professionally certified in the design and engineering of Data Centres, IP Telephony, Video surveillance and Structured Cabling solutions. He heads Norik Konsult, a practice that offers advisory, design and system planning help to upgrade or build a new Telephony, Security and Networking infrastructure.