Seeing the Light with CCTV Cameras
"The object is to identify and have clear documentation of an incident. The better you can see at all lighting levels, the better chance you have to identify and document," says Raul Calderon, product marketing manager at Sanyo Security Video, Chatsworth, Calif.
Placement of the camera is mostly driven by the application, availability of ambient light, proximity to infrared illuminators and practical installation limitations driven by structural design. For example, surveillance cameras used to monitor tollbooths must not only perform well in low light but must also be able to effectively compensate for severe highlight and backlight conditions. Vehicle headlights directly into the camera lens would render most cameras useless. In this application, the cameras should be mounted higher and facing down, out of the direct headlight beams, says Ken LaMarca, the director of security products for Sony Electronics' Broadcast and Professional Company, Park Ridge, N.J.
Ideal LocationsAdditional advancements in backlight compensation have also allowed indoor cameras looking toward an object positioned against a window to be more clearly identified by eliminating much of the excess light from the image. This allows an operator to clearly identify a person's face where a camera without backlight compensations would only see a dark image with very few recognizable features.
Cameras will always produce a better image when the majority of the lighting is from behind the camera or directed in the same direction as the camera. Indoor cameras should be placed away from light sources that are non-directional, such as florescent lighting. The best place for an indoor camera with relation to light, though rarely achievable, is a position where the light source will not hit the camera lens directly. The same principle holds true for outdoor cameras, although this can be even more difficult because the light source-the sun-is always changing, says Scott Jolma, product manager for Kalatel, Corvallis, Ore.
One of the latest improvement has been the use of CCD chips. They are more sensitive to low light and the IR spectrum. "CCD technology has significantly more sensitivity in the near infrared range than its predecessors. Near infrared extends beyond human perception but there is enough in low light that the sensor can pick it up and create a useful picture. The new generation of CCDs offer more features and improved performance," says Dean Lumb, director of product management, Silent Witness, Surrey, British Columbia.
Camera ImprovementsAdvancements in CCD design and digital signal processing will continue to improve the overall performance of CCTV cameras, including their ability to capture images in low light. Even though minimum illumination specifications are close to near darkness in many instances, the ability of a camera to process low light images and highly contrasted light has been more of an issue to CCTV system designers and camera engineers over the years. "The improvements in camera technologies affecting low light usability are in the dual mode cameras (color/monochrome) and digital slow shutter (DSS)," says Jolma.
The dual mode cameras have a mechanism built into the camera module that will remove the IR-cut filter from in front of the image sensor allowing an increased spectrum of light to be received. At the same time, the camera will remove the color information from the image creating a monochrome picture. This can make a camera 15 to 20 times more sensitive in low light conditions while allowing increased picture information-color image-during periods of good light availability. These cameras are still not as sensitive in low light conditions as a monochrome-only camera, which can be 10+ times more sensitive in low light conditions.
Typical lux ratings for a dual mode camera are 2 lux color, 0.1 lux monochrome, while a monochrome only camera could have a lux rating of 0.01 lux or better.
DSS is available in almost all camera modules designed for high-speed dome applications whether they be color, monochrome or dual mode. "DSS allows to speed up or slow down the effective shutter speed for the camera by layering multiple images internally in the camera electronics. This feature can increase the sensitivity of the camera by 15 times or more. The normal shutter speed for NTSC cameras is 1/60s. DSS allows us to reduce the shutter speed in steps down to as low as 1/4s for NTSC cameras," says Jolma.
"The result of B/W viewing at night is increased light sensitivity under very low light or no light conditions. Two types of day/night technology are currently used. Chroma-stripping technology strips the chroma signal from the video signal. The second is an IR cut filter removal technology, which removes the cut filter from the color CCD, which results in a B/W CCD for imaging at night. The second method results in far better performance characteristics. Sanyo uses the IR cut filter removal system to achieve light sensitivity down to 0.03 lux. Sanyo Security Video uses the IR cut filter removal system to achieve light sensitivity down to 0.03 lux," says Calderon.
Sanyo offers its line of day/night cameras, which senses the amount of light in the viewing area and automatically turns the IR cut filter on and off as required. As more precise color reproduction is essential in the color operation mode, the filter is turned on. In the B/W mode, clear, bright images-to a minimum required illumination of 0.03 lux-are produced by switching the filter off and increasing light sensitivity. The camera's sensitivity to exposed light allows it to automatically switch from color to B/W mode.
"Day/night operation is one recent development that has helped resolve the imaging problem caused by changing lighting conditions. Cameras with day/night operation deliver information packed with color images when lighting conditions permit and then switch to black and white operation when light levels drop," says Frank Abram, general manager, Panasonic Security Systems Group, Secaucus, N.J.
Other improvements in a camera's ability to perform well in low light conditions relate to technological advances in high gain/low noise AGC circuits and frame integration capabilities. One of Sony's UniDome models mechanically moves the color stripe filter away from the CCD device in low light conditions to dramatically increase the camera's low light performance, while maintaining highly accurate color detail during normal lighting conditions.
Take ELMO's HC7501 frame integration camera, for example, which incorporates a 1/2" sensor for better sensitivity, as well as a manual mode with the ability to select up to 510 frame integration. This is in addition to an auto mode that will handle bright field and 64-frame integration with just one setting. The broad dynamic range and integration function of the HC7501 is very forgiving in terms of what light levels are available versus what is required.
"The low-light functionality is always reliable. When there is less light, and with the HC7501 set up in Auto Mode, the camera starts to integrate relative to how much light is available. It in turn builds the image," says Dan McGinley, national sales manager, ELMO Manufacturing, Plainview, N.Y.
Also, Panasonic has released its WV-CP470 series of cameras, which combine the performance benefits of Panasonic's Super Dynamic II camera technology with day/night operation to provide high-quality images in virtually any lighting conditions. These cameras capture color images when lighting conditions permit-light levels as 0.8 lux-and highly detailed black and white images-as low as 0.1 lux-in dim lighting.
Panasonic offers the WV-CL920 series cameras that automatically switch from color to B/W operation with a minimum illumination of only 0.02 lux (0.002 fc). In addition, Panasonic's day/night cameras can distinguish between visible and IR lighting- useful in low light level applications where IR lighting is used.
As the demand for low light cameras grows, the percentage of camera products industry wide including excellent low-light performance also grows. "By incorporating the core imaging technologies into cameras at different price points, users can select the cameras that best suit their specific needs and budget," says Abram.
Moving OnAs is most everything affected in the security industry, technology will play an important role. "Going forward, the technological improvements will increase the sensitivity for all cameras. Cameras used in varying light conditions will be the primary application for dual-mode cameras, while indoor cameras that operate under controlled lighting can use more traditional technologies with backlight compensation," says Jolma.
"Camera performance improves with every new generation of products while remaining extremely affordable. Over time, the slight premium paid for a high quality, low-light camera will pale in comparison to increased costs in lighting/electricity to support a product with poor low light performance," says LaMarca.
"As long as the cameras are selected based upon their low-light specifications relative to a specific application, users can expect them to provide reliable low-light operation. The price of security cameras continues to drop as a result of increased demand, improved manufacturing efficiencies and more advanced imaging technologies. Advanced performance features can be found in a wide variety of cameras at different price points," says Abram.