The Lowdown on Low Light

An owl’s nocturnal vision is legendary. It can spot the slightest movement in the shadows of night and swoop down on unsuspecting prey.

Human visual perception in the hours from dusk to dawn falls far short of that mark. We might be able to sense movement, but discerning details like facial features, license plate numbers or the colors of objects and clothing diminishes in direct correlation to the waning light. It is precisely why the criminal element is so active at night.

Security cameras face similar limitations, because their design mimics the human eye. The sensor — just like the retina — needs a certain amount of light to project an image. The iris in both the eye and camera controls how much light is focused on the sensor/retina. The lower the available light, the worse the picture quality.

Over the past decade, however, manufacturers have made great strides in camera sensor, design and lens technologies to bring nighttime vision to new levels. True day/night cameras with mechanical IR-cut filters were the first on the scene, followed by day/night cameras equipped with infrared illuminators. Next to reach the professional surveillance market were thermal imaging cameras designed to detect heat and “see” in complete darkness. But neither IR-assisted surveillance nor thermal imagery produce detail or color at night — both critical factors for identification.

The newest generation of IP cameras adds another dimension to nighttime surveillance. “Lightfinder” technology combines acute light sensitivity with enhanced image processing, allowing the camera to see a wealth of visual detail — in color — even in poorly lit environments as low as 0.05 lux (think dead of night with minimal street lamps illuminating the area).

While each of these low-light technologies feature specific strengths to improve surveillance at night, it is knowing how to deploy the different cameras in strategic harmony to create a surveillance system that surpasses even an owl’s night sight.

 

Under the Setting Sun: True Day/Night Cameras & IR Illuminators

Day/night cameras use infrared (IR) cut filters to stream the light in the visual spectrum. During the daytime, the filters “cut out” infrared light, which would distort image color when it hits the sensor. At nighttime, the filters automatically retract to allow the infrared light to reach the sensor and increase the camera’s light sensitivity. At the same time, the camera converts to black-and-white mode, since color distortion would occur without the filter in place. In black-and-white, a true day/night camera can see images down to 0.008 lux.

IR illuminators — covert and non-covert — provide additional luminosity when ambient light is insufficient. Covert IR illuminators enhance a day/night camera’s ability to capture images in the invisible spectrum. Non-covert illuminators help the camera sensors to detect objects in the near-visible infrared spectrum.

Where they work well: Day/night cameras with IR illuminators are good in pitch-black environments such as warehouse entrances with no ambient light or darkened office building interiors with few windows. Covert illuminators are impossible to detect with the naked eye.

Where they fall short: Non-covert illuminators generate a red aura that intruders can spot with infrared detection devices. Illuminators also add cost to the surveillance installation, both in capital investment and labor, as well as power consumption. Furthermore, in smoke or haze, their perception is as foggy as the human eye. The cameras’ images are also produced in black and white, which can hinder identification.

 

Thermal Imaging Cameras

While day/night cameras focus on recognizing images in the visible light spectrum, thermal imaging cameras detect wavelengths far into the infrared spectrum. Since all people and objects emit some level of infrared radiation — commonly known as a heat signature — thermal imaging cameras can spot people and objects under any lighting condition, in smoky and hazy environments, as well as in direct sunlight that would typically blind conventional cameras. A thermal camera can transmit the image of a human silhouette even if the person is dressed all in white in a snow-covered field.

Where they work well: Being able to detect heat and “see” into the shadows makes thermal cameras a fit for neighborhoods concerned about light pollution. They are also perfect for surveillance of perimeters — such as waterfronts, remote power plants and tunnels and railway tracks — because their enhanced detection capabilities help security staff quickly spot intruders or people in danger and thus reduce the risk of crime, accidents and fatalities.

Where they fall short: Thermal cameras do not provide forensic or facial detail, which makes identification impossible. Mist, dust, haze, snow and rain can block heat signatures, making detection more difficult from great distances. Some materials such as concrete, marble and asphalt reflect ghost images, while others like glass can block the thermal camera altogether. Like day/night cameras, thermal cameras do not show real-world color in the scene — the images are black-and-white or in a thermal color palette, as in the photo on the previous page.

 

Color in the Dark: Lightfinder

While some movie buffs yearn for the elegance of black-and-white movies, the surveillance world — like the world of cinematography — realized that color adds a rich dimension of realism to a scene and it is no longer satisfied with monochromatic night vision. Camera manufacturers have responded with a new technology that revolutionizes low-light sensors and low-light lenses.

Aptly called Lightfinder, the technology works in concert with a network camera’s lens, sensor and advanced image processor to sense the light intensity of the scene and then leverage heavy processing inside the camera to produce the best image. This results in lifelike color and detailed video at night and in full sunlight.

The quantum leap in visual acuity amazes first-time viewers. Note the above screenshot photos. No artificial light, IR illumination or video trickery was used to create these images. In fact, the scene was close to pitch-black at 11 p.m.; yet, in the right-hand image you can see the person in an orange jacket clear as day. Maybe he is part of the repair crew making regular rounds, or maybe he is looking to inflict damage on a critical switch. Visual details like this can confirm his identity or trigger a security alert.

Where they work well: Lightfinder cameras fit into that surveillance niche where users need to capture true color and other forensic detail when there is minimal or nearly non-existent illumination. For instance, this IP technology can reveal the identity of ships approaching the port. It can help transit authorities monitor underground tunnels and long stretches of track across remote terrain. And thieves looking for easy pickings at unmanned construction sites in the dead of night will be captured in vivid detail.

Where they fall short: A Lightfinder-enabled camera is not meant for complete darkness like a thermal camera, and when the environment drops below a certain lux level (0.05), it will switch to black-and-white mode like a traditional day/night (IR-cut filter) camera. So while it does stream video in color at extremely low light levels — which of course provides security practitioners with a new edge for identification — your surveillance environment might best be served by combining a variety of “night eye technologies” to ensure full coverage.

 

Eliminating the Advantage of Darkness

Security professionals now have a full range of network cameras to capture images in low and no light. Users can choose surveillance cameras that can detect, observe and report events across the visual spectrum with as much forensic detail as needed.

Where privacy is an issue, thermal cameras can distinguish heat signatures while preserving anonymity because they do not reveal details like facial features. At the same time, they can differentiate between a fallen limb and a person, which would help users better identify false alarms. Should a threat be deemed real, Lightfinder cameras can kick into action, revealing critical details and forensic clues necessary to an investigation.

Surveillance tools, especially IP cameras, represent a constantly evolving technology. Manufacturers continue to invest in developing smarter, more nocturnally acute cameras to push back against the criminal element intent on mischief under a cover of darkness. While it is amazing to consider how far we have come, it is even more exciting to consider what well-funded R&D teams will come up with next to make the lives of lowlifes in low light even more miserable.

 

Fredrik Nilsson is General Manager of the Americas for Axis Communications and author of the book Intelligent Network Video. He is a regular expert contributor to STE and SecurityInfoWatch.com on topics of networked video surveillance systems and cameras.

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