If you’ve ever tried to capture surveillance images in a scene with highly contrasted lighting, such as near a large window or door, you’ve probably experienced the following results:
Your image was either overexposed in the lighter part of the scene, due to bright sunlight in the background, or it was underexposed in the shadowed areas, blacking out important details.
That’s because unlike the human eye, which can adapt to a wide variety of lighting conditions, a typical security camera has a limited dynamic range.
Dynamic Range Explained
In digital photography, the easiest way to think of dynamic range is the scale of light levels a camera’s sensor can capture – from the darkest black to the lightest white – in any single exposure, without losing image details.
Once a security camera exceeds its dynamic range, the image quality it produces will be degraded.
For example, in a scene with very bright light, a conventional security camera will shorten its exposure time, allowing less light in; however, this can leave darker areas of that scene without any detail (See example below left). Alternately, in scenes that are very dark, the camera will lengthen its exposure time to compensate for the lack of light. But that can leave bright areas of that scene looking overexposed, or very white (See example below right).
Strike the Right Balance with HDR
Properly illuminating a highly contrasted image is possible with a camera that uses High Dynamic Range (HDR).
In March Networks cameras, HDR extends the dynamic range of a camera by capturing multiple 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.
Just watch the difference that HDR can make. In this video, we compare the HDR technology in one of March Networks’ Outdoor IR Dome cameras to a standard camera’s Wide Dynamic Range (WDR).
To achieve these amazing results, an HDR camera 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.
Although digital WDR used to dominate the video surveillance industry, now features like HDR are much more common.
While the definition of WDR varies from manufacturer to manufacturer, generally, it refers to a camera’s ability to produce high-quality images across a wide range of light levels. March Networks’ cameras with digital WDR use advanced algorithms to lighten or darken a single exposure.
Although this kind of digital WDR process can help improve image quality in dynamic lighting conditions, 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.
Ideal for Security Applications
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 and credit unions 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.
As a reminder, HDR is available in most March Networks cameras including our new SE4 Series IP Cameras.
Do you have experience using HDR, or have a question about how it can help your security application? Share your thoughts and questions below: