Surveillance 101: Low-Light Cameras

An increasing number of end users today demand video surveillance cameras that are equipped with the technology to perform well in low-light or pitch-black conditions. Whether a surveillance camera is meant to monitor students within a hallway in a school, customers entering a store, or the license plate on a vehicle, installers need to plan for low-light situations as they occur in nearly all camera installations at some point in time.

Thanks to the introduction of high-powered processors, better optics, improved algorithms and advanced sensors, many surveillance cameras built today for low-light performance can deliver usable and high-quality images. With low-light technologies, IP cameras can provide more color video detail for users to more quickly identify people and objects of interest in dark areas. Exceptional video quality in low-light situations is now a reality.

In a market filled with numerous low-light cameras, selecting the right system can be more of a challenge than ever. Camera shoot-outs should be the norm for end-users and integrators who are concerned about image quality in any condition, and this is especially true for low-light applications. When evaluating low-light camera options for your customers, dealers and integrators should focus on the following five critical features and capabilities:

1. Maintaining a color image: When selecting a low-light camera, it is important to understand the objective for the use of that particular camera. Maintaining a color image can be important to clearly ascertain the color of clothing worn by a suspect or the color of a vehicle. City parking garages, city surveillance systems and retailers often require a surveillance camera that can maintain color images in low-light situations, such as when the store is closed and not all the lights in the store are turned on, or in a parking garage when the natural light is limited.

Another consideration when comparing low-light technologies is how long the camera maintains clear color video. IP cameras react at different light levels and also recover and settle at different paces while the camera tries to recover a proper exposure level. If not implemented properly, users can lose video for 5 to 10 seconds. Improvements with CMOS (complementary metal oxide silicon) image sensors have also advanced low-light video quality, as most CMOS imagers are now capable of maintaining color images at levels below 1 lux.

2. Noise: Often, users will find more noise and distortions present in low-light images, which will reduce the quality of the image. Noise occurs in dark environments where video sensors struggle to capture details. Automatic gain control (AGC) is a form of amplification where the camera automatically boosts the image received so that objects can be seen more clearly. As the AGC strengthens the signal to the camera to deliver a quality image, it typically increases the noise and overall size of the video.

Thus, with inefficient noise reduction comes the need for increased of hard drive storage and bandwidth which drives up the cost of ownership.

Many cameras include an Infrared Illuminator, which makes it possible to produce an image in a low-light setting. Once a camera goes into infrared imaging mode, the camera can no longer see in color and switches automatically to monochrome. This is ideal for applications where permanent color video is not a necessity.

3. True day/night: When determining low-light performance, consider the true day/night capabilities of the camera. Many of the sensors used in today’s security cameras are sensitive to both visible light – essentially what the human eye can see – as well as near-infrared light, which is emitted from sources such as sunlight, moonlight, halogen fixtures, etc.

True day/night delivers clearer images, which dramatically improves low-light operation. This is achieved by using an IR cut filter mechanism (IRCF), which removes the infrared filter from the imager to give the camera the ability to view near-infrared light. Keep in mind if a camera is “soft day/night,” it will transition to black-and-white video because it does not have a mechanism in place to remove the IRCF. Soft day night functionality does not utilize all visible and available IR light.

4. Shutter speed: In low-light situations, it is also important to ensure that the camera’s shutter speed is adequate to minimize blurring. Finding the right combination between shutter speed and a moving image – all while preserving the proper noise level, bandwidth level and low-light performance – can be a bit of a challenge.

Along with noise, a reduction in light can slow shutter speed, resulting in a 1/5-second shutter instead of a 1/30-second exposure. This can cause blurring motions in scenes, making identifying objects and people more difficult. Shutter speeds slower than 1/3 or 1/4 of a second can be problematic due to the resulting image blur. Even at half a second, a person can run through an area and not even be seen.

5. Beware the spec sheets: On paper, many cameras with a certain published lux level can look the same. To accurately test low-light effectiveness, integrators and users will often perform a head-to-head shootout in scenes below 1 lux, which is typically complete darkness. These shootouts provide a very telling story – for example, you can see first-hand how a camera running at a certain lux level produces so much noise so that a person’s face becomes blurry and the bandwidth consumption has quadrupled.

When conducting a low-light test, be sure to use the same lens and set the maximum shutter speed to the same setting on each camera.

Linda Natale is a product manager for Tyco Security Products. Request more info about the company at www.securityinfowatch.com/10547368.