In the closed-circuit surveillance system, the camera is also known as the camera or CCD (Charge Coupled Device) that is charge coupled device. Strictly speaking, the camera is the camera and the lens of the general term, but in fact, most of the camera and lens are purchased separately, the user according to the size of the target object and the distance between the camera and the object, through the calculation of the focal length of the lens, so each user needs the lens is based on the actual situation, do not think that the camera (head) on the lens has been. The main sensing component of the camera is the CCD, which has high sensitivity, small distortion, long life, anti-vibration, anti-magnetic field, small size, no residual shadow, etc. CCD is an electrically coupled device (Charge Couple Device) for short, which can change light into charge and can be stored and transferred, but also can be taken out of the storage of the charge to make the voltage change, and therefore it is the ideal video recording It is a new type of device that replaces the camera tube sensor. It is a new type of device that replaces the camera tube sensor. CCD's working principle is: the object being photographed reflected light, spread to the lens, the lens focuses on the CCD chip, the CCD according to the intensity of the light accumulates the corresponding charge, by the periodic discharge, resulting in the production of a picture of a picture of the electrical signals, filtering, amplification processing, through the camera's output terminal output a standard composite video signal. This standard video signal with home video recorders, VCD players, home video cameras, the video output is the same, so you can also be recorded or received on a television set to watch. CCD camera selection and classification CCD chip is like the human retina, is the core of the camera. At present, China does not have the ability to manufacture, most of the cameras on the market are used in Japan SONY, SHARP, Panasonic, LG and other companies to produce the chip, and now South Korea also has the ability to produce, but the quality will be a little inferior. Because of the chip produced by different levels of production, each manufacturer to obtain different ways and other reasons, resulting in CCD acquisition effect is also very different. At the time of purchase, you can take the following methods of detection: turn on the power, connect the video cable to the monitor, close the lens aperture, see if the image is completely black when there are bright spots, the screen snowflake big or not, these are the detection of the CCD chip is the most simple and direct method, and does not require other specialized instruments. Then you can open the aperture, look at a still life, if it is a color camera, it is best to ingest a brightly colored object, to see whether the image on the monitor is off-color, distorted, color or gray scale is smooth. A good CCD can well restore the color of the scene, so that the object looks clear and natural; while the image of the defective product will have a color deviation phenomenon, even if the face of a piece of white paper, the image will show blue or red. Individual CCD due to the dust of the production plant, CCD target surface will have impurities, in general, the impurities will not affect the image, but in low light or microscopic camera, small dust will also cause adverse consequences, if used for this type of work, must be carefully selected. 1, according to the imaging color division Color Camcorder: for scene detail identification, such as identifying the color of clothing or scenery. Black and white camera: for poorly lit areas and areas where lighting equipment can not be installed at night, only to monitor the location or movement of the scene, black and white cameras can be used. 2, according to the resolution of sensitivity and other divisions Image pixels in the 380,000 or less for the general type, especially 250,000 pixels (512 * 492), the resolution of 400 lines of the most common products. High-resolution type with more than 380,000 image pixels. Plate type. Pinhole type Hemisphere type. 3, divided by the size of the CCD target surface CCD chip has been developed in a variety of sizes: most of the chips currently used for 1/3 "and 1/4". In the purchase of cameras, especially for the camera angle has more stringent requirements, the size of the CCD target surface, CCD and the lens with the situation will have a direct impact on the size of the field of view and image clarity. 1 inch - target surface size of 12.7mm wide * 9.6mm high, 16mm diagonal. 2/3 inch - target surface size of 8.8mm wide * 6.6mm high, 11mm diagonal. 1/2 inch --Target surface measures 6.4mm wide * 4.8mm high, 8mm diagonal. 1/3 inch --Target surface measures 4.8mm wide * 3.6mm high, 6mm diagonal. 1/4 inch --Target surface measures 4.8mm wide * 3.6mm high, 6mm diagonal. - target surface size of 3.2mm wide * 2.4mm high, diagonal 4mm. 4, according to the scanning system PAL system. NTSC. China's use of interlaced (PAL) system (black and white for CCIR), the standard is 625 lines, 50 fields, only medical or other professional areas to use some non-standard system. In addition, Japan is NTSC, 525 lines, 60 fields (black and white for EIA). 5, according to the power supply 110VAC (NTSC is mostly such), 220VAC, 24VAC, 12VDC or 9VDC (microcamera is mostly such). 6, according to the synchronization method of division of internal synchronization: using the camera synchronization signal generated by the synchronization signal generation circuit to complete the operation. External synchronization: use an external synchronization signal generator, the synchronization signal into the camera's external synchronization input. Power Sync (linear lock, line lock): Vertical push synchronization is accomplished using the camera's AC power supply. External VD Sync: Input the VD sync pulse from the camera's signal cable to complete the external VD sync. Multi-camera external synchronization: Fixed external synchronization of multiple cameras, so that each camera can operate under the same conditions, due to the synchronization of the camera, so that even if one of the camera converted to other scenes, synchronized with the camera's picture will not be distorted. 7, in accordance with the degree of division, the CCD is divided into: Normal type of illumination required for normal operation 1 ~ 3LUX Moonlight type of illumination required for normal operation 0.1LUX or so Starlight type of illumination required for normal operation 0.01LUX or less Infrared type of infrared illumination, in the absence of light can be imaged in the case of the CCD color camcorder's main technical indicators (1) the size of the CCD, that is, the target surface of the camcorder. The original more than 1/2 inch, now 1/3 inch has been popularized, 1/4 inch and 1/5 inch has also been commercialized. (2) CCD pixels, is the main performance indicator of the CCD, which determines the degree of clarity of the display image, the higher the resolution, the better the performance of the image details. ccd is composed of an array of light-sensitive elements, each element is called a pixel, the more pixels, the more clear the image. Now most of the market to 250,000 and 380,000 pixels for the demarcation, 380,000 pixels or more for high-definition cameras. (3) Horizontal resolution. The typical resolution of color camcorders is between 320 and 500 TV lines, mainly 330 lines, 380 lines, 420 lines, 460 lines, 500 lines and other different grades. Resolution is expressed in terms of television lines (referred to as lines TV LINES), the resolution of the color camera is between 330 and 500 lines. Resolution and CCD and lens-related, but also with the camera circuit channel bandwidth is directly related to the usual law is 1MHz bandwidth equivalent to the clarity of 80 lines. The wider the bandwidth, the clearer the image, the greater the relative value of the line. (4) minimum illumination, also known as sensitivity. Is the degree of sensitivity of the CCD to ambient light, or CCD normal imaging needs the darkest light. Illumination unit is lux (LUX), the smaller the value, said the less light needed, the more sensitive the camera. Moonlight level and starlight level and other high sensitivity camera can work in very dark conditions, 2 ~ 3lux is the general illumination, and now there are less than 1lux of the ordinary camera came out. (5) scanning system. There are PAL and NTSC system. (6) camera power supply. AC 220V, 110V, 24V, DC 12V or 9V. (7) Signal-to-noise ratio. Typical value of 46db, if 50db, the image has a small amount of noise, but the image quality is good; if 60db, the image quality is excellent, no noise. (8) video output. Mostly 1Vp-p, 75Ω, all using BNC connectors. (9) lens mounting method. There are C and CS way, the difference between the two is that the light-sensitive distance is different. 2, CCD color camera adjustable features (1) the choice of synchronization A, for a single camera, the main synchronization methods are the following three: internal synchronization - the use of the camera's internal crystal oscillator circuit to generate synchronization signals to complete the operation. External synchronization - using an external synchronization signal generator to generate a synchronization signal sent to the camera's external synchronization input to achieve synchronization. Power synchronization - also known as linear lock or line lock, is the use of the camera's AC power supply to complete the vertical push synchronization, that is, the camera and power supply zero line synchronization. B, for multi-camera system, I hope that all the video input signals are vertically synchronized, so that when changing the output of the camera, will not cause picture distortion, but due to the multi-camera system of the camera power supply may be taken from the three-phase power supply in different phases, or even the entire system and the AC power supply is not synchronized, at this time, measures can be taken are: are used with the same synchronization signal generated by the external synchronization signal generator The synchronization signal generated by the same external synchronization signal generator is fed into the external synchronization input of each camera to adjust the synchronization. Adjust the camera's "phase adjustment" potentiometer, because the camera in the factory, its vertical synchronization is the same phase with the rising edge of the AC power is over the zero point, so the use of phase delay circuit can make each camera has a different phase shift, so as to obtain the appropriate vertical synchronization, phase adjustment range of 0 to 360 degrees. (2) automatic gain control All camcorders have a signal from the CCD will be amplified to the level of video amplifier can be used, the amplification of the large amount of that gain, equivalent to a higher sensitivity, which can be made in the dim light sensitive, however, in the bright light of the environment amplifier will be overloaded, so that the video signal distortion. For this reason, the need to use the camera's automatic gain control (AGC) circuit to detect the level of the video signal, switch AGC at the right time, so that the camera can work in a wider range of light, which is the dynamic range, that is, in the low-light automatically increase the camera's sensitivity to improve the intensity of the image signal to obtain a clear image. (3) background light compensation Usually, the camera's AGC operating point is determined by the average of the contents of the entire field of view to determine, but if the field of view contains a very bright background area and a very dark foreground target, the AGC operating point determined at this time may not be enough for the foreground target is not suitable for the background light compensation is likely to improve the foreground target display conditions. When the background light compensation is on, the camera only on the entire field of view of a sub-area of the average to determine its AGC operating point, then if the foreground target is located in the sub-area, the foreground target is expected to improve the visibility. (4) electronic shutter in the CCD camera, is optically controlled image surface charge accumulation time to manipulate the shutter. Electronic shutter control camera CCD accumulation time, when the electronic shutter is closed, the NTSC camera, its CCD accumulation time of 1/60 seconds; for PAL cameras, it is 1/50 seconds. When the electronic shutter of the camera is open, the electronic shutter covers the range from 1/60th to 1/10,000th of a second in 261 steps for NTSC cameras and from 1/50th to 1/10,000th of a second in 311 steps for PAL cameras. When the electronic shutter speed increases, in the time allowed for each video field, the light focused on the CCD is reduced, the result will be a reduction in the sensitivity of the camera, however, higher shutter speeds for the observation of moving images will produce a "stop-motion" effect, which will greatly increase the dynamic resolution of the camera. (5) White balance White balance is only used for color cameras, its purpose is to achieve the camera image can accurately reflect the scene conditions, there are two ways of manual white balance and automatic white balance. A, automatic white balance Continuous mode - at this time, the white balance setting will be adjusted continuously with the change of color temperature of the scene, the range of 2800 ~ 6000 K. This way for the color temperature of the scene in the shooting during the continuous change of the occasion is the most appropriate, so that the color performance is natural, but for the scene in little or no white When the continuous white balance .
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