Whether or not it’s deserved, IP cameras have developed a reputation for poor performance in low light. And because low-light conditions exist with nearly all camera installations, this perception has inhibited some organizations from adopting the technology, in spite of its many strategic and far-reaching benefits.
The challenges have had less to do with delivering the video over an IP network than with the CMOS sensors that most IP cameras use. Historically, these sensors have been able to deliver higher megapixel resolution, but they weren’t able to match the CCD sensors often used in analog cameras for low-light performance. Thus, some IP cameras generate grainy images at low light, resulting not only in decreased picture clarity but also in higher bandwidth and increased storage, since compression techniques interpret the graininess as motion in the scene.
Over the last year, advancements in technology have enabled the IP camera to function as a more useful tool in low-light situations. Camera manufacturers have been able to leverage advances in sensors, encoding and processing power born in the automotive and other industries to resolve many of these issues. And High Profile H.264 compression helps to more effectively manage bandwidth usage, while more sensitive elements in the sensors provide higher-quality images.
Companies hoping to benefit from these advances should look for the following features in low-light IP cameras:
1. True Day-Night
True Day Night capability is achieved by using an IR Cut-Filter Mechanism (IRCF). Many of the sensors used in today’s security cameras are sensitive to both visible light (380nm~740nm) - essentially what the human eye can see - as well as near infrared light (750nm~1100nm), which is emitted from sources such as sunlight, moonlight, halogen fixtures, etc.
Unfortunately, to produce accurate colors, most of the IR light needs to be blocked or filtered out. Many cameras do this by using an IR Cut Filter, which sits in front of the sensor like a pair of sunglasses. With this True Day Night /IRCF feature, the camera is equipped to remove these "sunglasses" when the light levels drop below a certain threshold. This enables more of the visible light and available IR light to get to the sensor, dramatically improving low-light performance.
Because of the filtering or blocking of the IR light, color accuracy usually suffers in this mode. Most implementations also remove all color information, yielding a black-and-white image that is not only vastly more usable but also cleaner without chroma noise. This improves image clarity while decreasing noise or graininess in the image, which can be interpreted as motion in the encoder. When the encoder compresses an image with a higher level of motion or noise, the bandwidth consumption can skyrocket.
One other True Day Night technology differentiator is what manufacturers do when the IRCF is in the "out" or removed position. The better ones replace the IRCF with a piece of dummy glass to help minimize the spectral offset between visible and IR light. This helps keep the image in focus and retain auto focus stability.
Be aware there are cameras that have a "Quasi" or soft Day Night (SDN) feature - this is not the same thing as True Day Night. These cameras go black-and-white when the light levels are low but they have no mechanism to remove the IRCF "sunglasses," so they cannot take advantage of all the visible and IR available light. Marketing literature has made this a source of confusion in our industry, so make sure you know which Day Night implementation your cameras of interest have.
Also note that the use of IR-corrected lenses is highly recommended with True Day Night cameras. Since visible and IR light are in different wavelength bands, they focus at different points - creating a potential problem of focus shift when switching between color and black-and -white modes. A good quality IR-corrected lens can compensate, meaning fewer service calls to correct the focal points.