| Q1. What makes a good images in CCTV ? |
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| Ans. Following factors determine the quality of images in CCTV systems-
Proper selection of good quality lens: Lens should be selected according to the distance between the camera and the place of Interest. In most cases the cost of the system can be saved by using the correct lens for the CCTV camera.
Lighting Conditions: In low lighting conditions Day/night camera and IR Camera should be used. The Latest Technology WDR cameras gives clear images in backlighting conditions.
Resolution and Quality of camera: A good resolution camera can be of 580 to 600 TVL. One can also go for Megapixel IP camera. Latest IP camera with HD technology gives superior picture rendering and zoom.
Placement of camera: Placement of camera is highly important. A good camera will be useless until its feild of view is covering the areas properly. In events where the fraudster is to be recognized
Video compression technology: This is important if the CCTV footage is recorded using a DVR. Since in most of the cases, CCTV footage is required for post-incidence investigation. A good quality camera becomes unimportant if it is been recorded in a low quality format like MPEG. High quality compression like H.264 is ideal for recording CCTV images. New Technology in CCTV Storage like HDD ( upto 2 Tb) can store good quality images for a longer period of time.
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| Q2. What is Videosignal ? |
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| Ans. A Video signal capable of reproducing a Video picture is generated in an imager or
Camera Sensor.
A two dimensional picture can be represented as a two dimensional array (like a checkered page) of picture elements (pixels), each one containing data on color and brightness.
The Video signal of CCTV-surveillance presents the camera output as a continuous waveform which is obtained by streaming the data of each pixel, one by one, when scanned from the first to the last of any frame or picture.
The waveform provides a one dimensional sequence of analog data that are fed to the monitor device. To achieve a correct reproduction of the image, timing signals are added according to specific protocols, to indicate the start of a line, the serial number of the line, and, after the last pixel, a signal is included to perform the vertical retrace and prepare to scan the next field.
A composite color signal consists of the standard monochrome signal with color information added.
In North America the video signal is a standard, called NTSC (National Television Standards Committee), while in Europe the standard is PAL or SECAM in different places. Monitor and camera must operate according to the same standard.
Sound and video are completely separate in analog TV. A color TV signal starts off looking just like a black-and-white signal, but an extra chrominance signal is added to provide color data.
In a CCTV-surveillance camera signal there are no radio frequency waves to deal with, therefore the monitor has no tuner to pick up the right channel. The Video signal is fed directly to the screen according to the proper scanning protocol.
To be fed to a computer screen, instead of an analog monitor, the Video signal of a CCTV-surveillance camera has to be digitized by the grabber card. When so transformed the digital image can be compressed according to usual computer protocols (JPEG, MPEG etc.) and is no more dependent on synchronization signals for correct display.
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| Q3. What is Illumination ? |
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| Ans. A scene presents different colors, surfaces and materials that reflect varying amounts of light. Before selecting equipment, one should determine the minimum light level that will arrive from the scene to the camera lens.
The target area can be lighted by natural or artificial light sources.
The illumination of a scene describes the quantity of light reflected by the visible objects to the camera lens. This is a quantity expressed in Lux, measurable with an instrument called photometer. Even without such an instrument one can see from available tables that there is a huge difference between the light available in a moonless night, and that of full sunlight.
Under a given lighting condition, black absorbs most of the light available and reflects only a minimum part. So do also rugged materials and rough surfaces. On the contrary flat and bright colored surfaces reflect most of the light falling on them.
The amount of reflected light collected from any setting depends on the amount of lighting available and on the scene reflective characteristics. The human eye can readily adjust to widely varying illumination levels. On the contrary, optical viewing and recording systems have much reduced latitude of adaptation to conditions suitable for the display of interpretable pictures.
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| Q4. What is Resolution ? |
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| Ans. ability to resolve or see distinctly small details in an image. Resolution for CCTV cameras (as well as for TV monitors and recorders) is usually specified in terms of lines of resolution. The number of TV lines in the video produced by the CCTV-surveillance camera is a measure of picture resolution (sharpness) also described as quality of definition and clarity of a picture.
If a sequence of pictures, containing a progressive larger number of finer distinct horizontal or vertical lines, are captured by a camera and displayed by a monitor, there will be a limit to the number of separate lines that can theoretically be seen clearly. The more the lines, the higher the resolution and the better the picture quality. CCTV cameras range from 200 to more than 1,000 lines of resolution.
The larger the number of TV lines, the better the resolution and the overall picture quality. Black and White cameras have usually higher resolution than Color ones. Resolution is directly proportional to the number of picture elements (pixels) in the solid state chip sensor (imager).
There are two different types of resolution. They are mentioned as under :-
Vertical resolution refers to the number of horizontal lines resolvable .Vertical resolution is constant for a given scanning system (NTSC, PAL or SECAM), between 350 and 400 lines.
Horizontal resolution refers to the number of vertical lines resolvable. The color cameras used in CCTV-surveillance systems generally offer horizontal resolution between 330 and 480 lines. Over 600 lines is considered high resolution.
If different elements of a CCTV-surveillance system are capable of different numbers of resolution lines, the overall resolution of the system will be that of the least line number element.
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