【英文原文】查看這里

　　有一個簡單的規(guī)則，它決定了任何CCTV工程的成效-沒有光就沒有圖像。在本文中，Ian Crosby(博世安防系統(tǒng)照明 歐洲產(chǎn)品營銷經(jīng)理)探討了在現(xiàn)代視頻監(jiān)控系統(tǒng)中紅外(IR)照明在帶寬上的效果和如何使用IR照明能夠減少存儲的成本。

夜間監(jiān)控要采集到高質量的圖像有許多要克服的挑戰(zhàn)

　　在低照度條件下管理帶寬

　　無論是模擬還是數(shù)字(如編碼算法像H.264壓縮模擬視頻以用于IP系統(tǒng))，幾乎所有的CCTV攝像機都可以在白天光線充足情況下捕捉到有用的圖像。但是，卻是你的安防系統(tǒng)平臺在夜間工作的怎么樣決定了其整體功效，因為大多數(shù)犯罪在黑暗中的脆弱時間里發(fā)生，今天的安防系統(tǒng)需要配備二十四小時監(jiān)控設備?！　?/P>

　　大多數(shù)犯罪正是利用監(jiān)控系統(tǒng)的弱點在晚上作案

　　絕大多數(shù)現(xiàn)代安防攝像機規(guī)格看起來能在非常低的光照條件下有效運作，但他們標注的照度率非常低，通常在0.1lux以內(nèi)。但是人們普遍的認識是如果沒有專業(yè)的CCTV照明—無論是白光還是紅外，大多數(shù)攝像機在黑暗壞境和夜間只能捕捉到低質量的“嘈雜”圖像。

　　改善圖像質量和可用性對特殊安全照明有明顯好處。然而，對CCTV用戶來說另一個關鍵的好處到現(xiàn)在才逐漸顯現(xiàn)。當光線水平下降的時候，來自網(wǎng)絡的每個攝像機的壓縮視頻流比特率有顯著增加。 這種增加的比特率，如果不加以解決，將導致系統(tǒng)的總存儲成本大幅增加。

　　了解夜視安防攝像機的自動增益控制(ACC)

　　為了理解為什么低照度監(jiān)控對帶寬有如此高的要求，以及要以更高的比特率來傳輸視頻，我們需要考慮自動增益控制(AGC)。

　　AGC是提高在低照度條件下信號強度的攝像機技術。它的工作原理很簡單，放大圖像;這種放大的效果不過是增加了視頻信號和。

　　來看一個典型的安防工程：現(xiàn)場監(jiān)控攝像機在白天傳遞良好的可用的圖像，但是在黑暗降臨使相機的AGC功能開始生效了。越是黑暗它的AGC增加幅度越大，攝像機抓取的圖像也變得顆?；汀班须s”。最終圖像被“雪花”完全遮蔽了，幾乎毫無用處。

　　那么，為什么“嘈雜”的夜間監(jiān)控視頻影響比特率呢?[nextpage]

　　視頻壓縮算法的影響

　　要理解為什么比特率會上升，重要的是要對視頻壓縮算法如何工作有一個基本的理解。壓縮的基本原理是消除所有非本質的信息以及減小文件的大小。所有的壓縮均需要在圖像質量和文件大小之間進行一個折中。更高的壓縮率可以是文件大小更小但是圖像質量會降低;而較低的壓縮率可以產(chǎn)生高質量的圖像但是需要更大的文件尺寸。

低照條件下產(chǎn)生的問題將大大較少和限制監(jiān)控攝像機技術

　　對于大多數(shù)設備，攝像機的幀率和分辨率需要進行調(diào)整以適應應用的需要;這些參數(shù)通常是前期指定的。這樣有一個明顯的好處是降低幀率和減少分辨率(更低的比特率)，同時也有一個主要的有點。犧牲幀率和分辨率的結果是低質量的看起來“波濤洶涌”的監(jiān)控視頻畫面，這可能錯過所記錄的時間中的關鍵時刻。

　　當今最流行的視頻壓縮引起結合了JPEG、MPEG或者M-JPEG。最近的是新的H.264算法，它比MPEG4壓縮技術少約30%的帶寬，而比M-JPEG的效率高80%。然而所有算法都有共同的的減少信息的原則;減少不相干信息，消除不被人眼注意的視頻信號(比如細微的顏色變化)或從相同幀或者中間幀刪除重復的冗余信息，比如大的色彩區(qū)塊或者固定物體。

　　低照度監(jiān)控、壓縮品質和比特率之間的關系

　　在晚上相機通常鏡頭視野里的活動和運動較少，因而夜間視頻應該以較低的比特率來存儲視頻。然而，攝像機采集增加的的圖像噪點引起會干擾視頻編碼器的壓縮算法。準確的說，壓縮算法將噪點通過AGC增強圖片看作是現(xiàn)場的運動，因此有用的信息就不能減小不相干或冗余的體積。由于這樣夜間監(jiān)控視頻壓縮得較少，體積也就比它應有的大小更大?，F(xiàn)在清楚了，低照度錄監(jiān)控、壓縮品質和比特率三者之間有直接的關系。

　　比特率對安防系統(tǒng)成本的影響

　　不斷增長的存儲空間是昂貴的，并且是現(xiàn)代數(shù)字監(jiān)控系統(tǒng)的主要開支之一

　　比特率是攝像機或編碼器每秒傳輸?shù)拇罅繑?shù)據(jù)。也是每秒鐘必須被保存并寫入存儲介質的大量數(shù)據(jù)。攝像機或編碼器的每個通道的比特率越高，系統(tǒng)整體存儲的要求就越高。逐漸增加的存儲空間是昂貴的，并且是現(xiàn)代數(shù)字監(jiān)控系統(tǒng)的主要開支之一。

　　紅外與編碼相結合(IP和混合)的好處

　　與其不斷的給一個安防系統(tǒng)增加存儲，不如解決問題的根本所在—夜間的高比特率。首先看起來一個快速的解決方法是簡單的禁用攝像機的AGC功能。這或許可以減少比特率，但代價是犧牲所有重要的圖像細節(jié)。禁用使相機的AGC功能會導致監(jiān)控畫面的畫質就算不是沒有用，也會讓畫質變的糟糕。一個更好解決方案是在鏡頭上安裝節(jié)能紅外照明。使用紅外時，攝像機就沒必要采集那么多畫面，編碼器算法也不會那么多，DVR和其他存儲設備能以最佳效果工作。[nextpage]

　　使用紅外照明時安防攝像機傳送高分辨率、高質量的圖像噪點幾乎為零的夜間監(jiān)控視頻證據(jù)，現(xiàn)在我們知道，更少的視頻噪點等于更佳的壓縮品質、更少的比特率和存儲需求。

　　使用紅外照明能使安防攝像機傳送更分辨率的也將愛你監(jiān)控視頻

　　安防攝像機照明和圖像的質量

　　最基本的，紅外是光線。光線是人眼看不見的，但它被單色(黑白)和雙模式監(jiān)控攝像機所使用來揭示可能對人眼來說完全黑暗的夜間場景。記住我們的金科玉律，沒有光就沒有畫面。

　　紅外防止嘈雜的夜間圖像和導致高比特率的一連串事件，過多的存儲要求和不必要的開支。此外，某些紅外照明器功能創(chuàng)新了3D擴散(黑鉆石)技術，以引導光線給攝像機視野的前景和背景，以產(chǎn)生完美均勻照亮的夜間圖像，避免因其他一些紅外照明器造成的熱點和曝光過度。要記住我們的宗旨是，圖像的質量要高，而存儲需求和系統(tǒng)整體的成本要低。

　　在數(shù)字視頻監(jiān)控應用中利用IR減少存儲需求

　　雖然使用紅外照明來提高圖像的質量和可用性廣受安防產(chǎn)業(yè)的認可，但它作為一個帶寬管理工具來使用可能會令人感到驚訝。由于存儲是運行一個安防系統(tǒng)導致的最大的開支之一，因而把IR來作為一個減少數(shù)字視頻應用中的存儲需求有效的工具，歡迎并要鼓勵這樣做將帶來驚喜。

        作者：Ian Crosby　　博世安防系統(tǒng)EMEA地區(qū)照明產(chǎn)品營銷經(jīng)理

【英文原文】下一頁[nextpage]

Benefits of using infrared (IR) illumination in modern surveillance environments

　　There is a simple rule which determines the effectiveness of any CCTV installation - without light there can be no picture. In this article, Ian Crosby (EMEA Product Marketing Manager - Illumination of Bosch Security Systems) looks into the effects of infrared (IR) illumination on bandwidth and how the use of IR lighting can contribute to reduced cost of storage in a modern video surveillance system.

　　Managing bandwidth in low light conditions

　　Whether analogue or digital (where encoding algorithms like H.264 encode analogue video for use with IP systems), virtually all CCTV cameras can capture good, useable images in bright, daytime conditions. However, it is how well your security system performs at night that determines its overall effectiveness, and since most crime takes place during the vulnerable hours of darkness, todays security systems need to be equipped for round-the-clock surveillance.

　　It is precisely at night that most criminals will try to take advantage of weaknesses in surveillance systems

　　The specifications of most modern security cameras state extremely low lux ratings - often in the range of 0.1 lux - seeming to suggest effective operation in very low light conditions. It is generally accepted however that without specialist CCTV illumination - be it visible white light or infrared - most cameras will only capture low quality, "noisy" images in dark, night-time conditions.

　　Improving image quality and usability is one obvious benefit of specifying security illumination. However, another key benefit for CCTV users is only now coming to light. When light levels drop there is a significant increase in the bit rate of the encoded video stream from each camera in a network. This increased bit rate, if left unaddressed, will cause a substantial increase in the total storage costs of the system.

　　Understanding automatic gain control (ACC) in night vision security cameras

　　To understand why low light surveillance has such a higher bandwidth requirement and transmits video at a higher bit rate, we need to consider automatic gain control (AGC).

　　AGC is camera technology, which increases signal strength in low light conditions. It works simply by amplifying the image; the effect of this amplification however is increased video signal and in turn increased image noise.

　   Take a typical security installation: on-site surveillance cameras deliver good, useable images during the day but as darkness approaches the cameras AGC function kicks in. The darker it gets the more AGC increases in magnitude and the images the cameras capture become grainy and "noisy". Eventually the image is completely obscured by "snow" and becomes practically useless.

　　So why does "noisy" night-time surveillance video affect bit rate?

　　Impact of video compression algorithms

　　To understand why there is a rise in bit rate, it is important to have a basic understanding of how video compression algorithms work. The basic principle of compression is to eliminate all unessential information and reduce file size. All compression requires a compromise between image quality and file size. Higher compression ratios enable smaller file sizes but low quality images; lower compression ratios produce high quality images but need larger file sizes.

　　Problems of low light conditions can be greatly reduced or eliminated with the proper surveillance camera technology

　　With most installations, camera frame rate and resolution are adjusted to suit the applications needs; these parameters are generally specified up-front. While there is an obvious benefit to lowering frame rate and reducing resolution (lower bit rate) there is also a major disadvantage to doing this. Sacrificing frame rate and resolution results in low quality "choppy" surveillance video that can miss critical moments in a recorded event.[nextpage]

　　Todays most popular video compression engines incorporate JPEG, MPEG or M-JPEG. Most recent is the new H.264 algorithm that uses approximately 30% less bandwidth than MPEG4 compression technology, which is itself 80% more efficient than M-JPEG. All however share common reduction principles; irrelevancy reduction, which removes sections of the video signal not noticeable by the human eye (like subtle colour changes) or redundancy reduction which removes duplicated information from either the same frame or between frames, large block areas of colour or stationary objects for example.

　　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, DVRs 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.[nextpage]

　　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.