主页（http://www.pttcn.net）：在现代监控环境中使用红外(IR)照明的好处【中英对照】(3) Relationship between low light surveillance, compression and bit rate At night there is generally less activity on scene and less movement in the cameras field of view, therefore night-time video should be able to be stored at a lower bit rate. However, image noise caused by increased camera gain can interfere with compression algorithms used by video encoders. To be precise, compression algorithms interpret noisy AGC enhanced images as movement on-scene and therefore useful information that cannot be reduced in size by irrelevancy or redundancy. Because of this night-time surveillance video is less compressed and larger in file size than it should be. It is now clear that there is a direct relationship between low light surveillance, compression and bit rate. The effect of bit rate on cost of a security system Increasing storage space is a costly exercise and one of the principal expenses of a modern digital security system Bit rate is the amount of data transmitted per second by a camera or encoder. This is also the amount of data per second, which must be retained and written to the storage medium. The higher the bit rate of each channel (camera or encoder) the greater the overall storage requirement of the system. Increasing storage space is a costly exercise and one of the principal expenses of a modern digital security system. The benefits of combining infrared and encoding (IP and Hybrid) Rather than continually adding storage to a security system it is best to address the root cause of the problem - high bit rate at night. At first it seems a quick fix would be to simply disable the cameras' AGC function. While this would reduce bit rate, it would be at the expense of all important image detail. Disabling the cameras' AGC function would result in poor quality, if not useless, surveillance images. A better solution is to install energy efficient infrared illumination on scene. When used with infrared, high camera gain becomes unnecessary and compression algorithms in encoders, DVR's and other recording equipment work to optimum effect. Using infrared illumination enables security cameras to deliver high resolution, evidentiary quality night-time surveillance video with virtually zero image noise, and as we now know, less video noise equals better compression, reduced bit rate and reduced storage requirements. Using infrared illumination enables security cameras to deliver high resolution night-time surveillance video Security camera lighting and picture quality At the most basic level, infrared is light. Light that is invisible to the human eye but which is used by monochrome and dual mode surveillance cameras to reveal night-time scenes which would appear completely dark to the human eye - remember our golden rule, without light there can be no picture. Infrared prevents noisy night-time images and the subsequent chain of events that causes high bit rates, excessive storage requirements and unnecessary expense. In addition, certain infrared illuminators feature innovative 3D diffuser (Black Diamond) technology which directs light to the foreground and background of the cameras field of view, for perfectly evenly illuminated night-time images, free from hotspots and overexposure caused by some other IR illuminators. Remember the higher the quality of the image, the lower the storage requirement and overall cost of the system. Using IR to reduce storage needs in digital video applications Although the use of infrared lighting to improve image quality and usability is widely understood by the security industry, its use as a bandwidth management tool may come as a surprise. Given that storage is one of the biggest expenses incurred when operating a security system, that surprise is a welcome one and should encourage the use of IR as an effective tool for reducing storage needs in digital video applications. (中国集群通信网 | 责任编辑：陈晓亮) |
