A study of bandwidth shows that as available light decreases, bandwidth usage for IP surveillance cameras increases. Use of infrared illumination keeps the bandwidth usage level.
Photo credit: Image courtesy Bosch Security Systems Inc.
A comparison of infrared illumination. In the top image, with infrared off the ambient visible lighting is .08 lux and bitrate is 13.4 MBPS. With infrared on (lower), ambient visible lighting is still .08 lux and bitrate is 1.21 MBPS - a reduction of 91%.
Photo credit: Image courtesy Bosch Security Systems
Virtually all CCTV cameras produce usable surveillance images under daytime conditions, but when faced with challenging lighting, some IP cameras encounter issues with image quality and bandwidth management. And, since today’s security systems require 24/7 performance, it is often the nighttime function that determines overall system effectiveness.
CCD and CMOS image sensors are designed to see light -- making pictures or videos in the process. If there is no light, there can be no picture. Many cameras today have very low lux ratings, often in the range of 0.1 lux. While these camera specifications suggest effective operation under low light, the security industry generally accepts that low-light environments result in noisy, low-quality images. As image noise increases, there is a corresponding increase in the demand for network bandwidth -- or the number of bits transmitted in one second.
To understand the reasons behind higher bandwidth in low light, it is important to consider automatic gain control (AGC), a camera technology that increases signal strength under low-light conditions. AGC works simply by amplifying the image. However, the effect of the amplification is an increase in both the video signal and the noise. As the scene becomes darker and darker, AGC increases in magnitude, creating more noise in the process. Eventually, snow and graininess obscure the nighttime image. Under these conditions, bitrates can be many times greater than the daytime bitrates for static, non-moving images.
This rise in bitrates directly correlates to the interference of AGC with compression algorithms used in today’s IP cameras. The basic principle of compression is to eliminate superfluous information to reduce file size. Compression requires a compromise between image quality and file size. Higher compression ratios deliver smaller file sizes but lower quality images. Lower compression ratios produce higher quality images but larger file sizes.
Today’s popular compression engines typically use one of two reduction principles:
- irrelevancy reduction - removes parts of the video signal not noticeable by the human eye, such as subtle color changes
- redundancy reduction - removes duplicated information, such as large uniform areas of color or stationary objects, either from the same frame or between frames
Compression algorithms interpret the snow and graininess of AGC-enhanced images as useful information, such as image details or motion, which cannot be reduced by either irrelevancy or redundancy. Consequently, nighttime images are less efficiently compressed and have larger file sizes.
At first, it seems that the quickest fix to this issue would be to disable AGC. This strategy would indeed reduce bitrates but at the expense of image detail. Doing so would result in very poor -- if not useless -- nighttime images.
In many applications, integrators will alter frame rates and resolution to suit the end user’s bandwidth or storage limitations. For example, if either network bandwidth or storage space is insufficient, a common strategy is to reduce the frame rate, resolution or both. However, there are disadvantages to this approach. Sacrificing frame rate and resolution results in low-quality “choppy” video that may miss critical moments in a security event. Additionally, low frame rates and resolution significantly degrade the performance of video analytics software, if used.
The Effects of Adding Infrared
The best solution to ensure effective nighttime performance of IP-based systems is to apply infrared illumination to a scene. Infrared illumination is field-proven technology for high-performance night vision, and its use in today’s surveillance video applications extends into bandwidth management as well.
At the most basic level, infrared illumination is light. Although invisible to the human eye -- which would see a completely dark scene -- infrared illumination is a form of light that modern surveillance cameras can use to create images. Providing the IP camera with the right amount of infrared illumination will ensure that nighttime images are high signal, low noise. Under these conditions, AGC becomes unnecessary and compression functions work efficiently. In fact, adding infrared illumination to a system can decrease bitrates by up to 90 percent, resulting in bandwidth requirements that are more similar to day-time levels. Useful for its bitrate reducing effects, infrared illumination is a growing necessity for improving network performance in IP-based security systems.
The use of infrared illumination extends into storage as well. If a camera transmits video at a certain bitrate across a network to be stored, then the video will consume disk space at exactly the same rate. For example, a 1 Mbps video stream will use 1 Mb of space in one second, or about 1/8 = 0.125 Megabytes per second, which equates to 0.125 x 3,600 = 450 Megabytes per hour -- about 11 GB per day or 75 GB per week. Since there is a direct correlation between bitrate and storage requirements, infrared illumination can be an effective strategy for reducing storage demands in IP video applications. This issue is especially important because disk space is one of the most expensive components of a surveillance system.
In summary, infrared illumination not only increases the quality of the images recorded, it also reduces required disk space, improves bandwidth, and enables enhanced nighttime surveillance.
Available options for adding infrared illumination are IP cameras offering integrated infrared or standalone infrared illuminators placed near existing cameras. By adding infrared illumination, achieving improved bandwidth management for existing IP surveillance systems is possible without significant cost. And, for new systems, infrared illumination should be a consideration for any site that requires 24/7 surveillance of areas with challenging lighting conditions.
About the authors: Hamish Dobson is a product manager for Bosch Security Systems. Willem Ryan is the product marketing manager for Bosch’s line of active-infrared, extreme environment and license plate capture cameras and related video devices. They can be reached at firstname.lastname@example.org and email@example.com.