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Fight Back Against Harsh Backlight with High Dynamic Range

A comparison of shots taken with a camera using no WDR, WDR, and HDR.

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 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. 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.

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 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.

To do this, 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.

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.

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.

As you’ll see from the images below, an HDR camera outperforms a camera with digital WDR by providing more detail in both the darkest and brightest areas of the scene.

A shot taken with a camera using no WDR.
Camera with no WDR

A shot taken with a camera using WDR.
Camera with WDR

A shot taken with a camera using HDR.
Camera with HDR

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.

Do you have experience using HDR, or have a question about how it can help your security application? Share your thoughts and questions below:

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