Camera introduction
Camera
The camera part is generally installed at the scene, which includes the camera, lens, protective cover, bracket and electric pan / tilt. Its role is to take a picture of the surveillance area and convert it into an electrical signal.
The camera is divided into color and black and white. The general black and white camera is more sensitive than the color and is more suitable for places with insufficient light. If the purpose of use is only to monitor the position and movement of the scene, the black and white camera can be used; For details of camera objects, such as distinguishing the colors of clothes and scenes, it is better to use color.
The specifications of the camera can be divided into 1 / 3〃, 1 / 2〃 and 2 / 3〃, etc. The installation methods are fixed and with a gimbal.
In the closed circuit monitoring system, the camera is also called a camera or CCD (Charge Coupled Device), which is a charge coupled device. Strictly speaking, the camera is the general term for the camera and the lens. In fact, most of the camera and the lens are purchased separately. The user calculates the focal length of the lens according to the size of the target object and the distance between the camera and the object, so each user The required lenses are all based on the actual situation, do not think that the camera (head) already has a lens.
The main sensing component of the camera is the CCD, which has the characteristics of high sensitivity, small distortion, long life, anti-vibration, anti-magnetic field, small size, and no residual image. CCD is the abbreviation of Charge Couple Device, which can Turning light into electric charge can store and transfer the electric charge, and can also take out the stored electric charge to change the voltage, so it is an ideal imaging element. It is a new device to replace the camera sensor.
The working principle of CCD is: the object reflects light, propagates to the lens, and focuses on the CCD chip through the lens. The CCD accumulates the corresponding charge according to the intensity of the light, and periodically discharges to generate an electrical signal that represents a picture. After filtering and amplification, a standard composite video signal is output through the output terminal of the camera. This standard video signal is the same as the video output of home video recorders, VCD players, and home video cameras, so it can also be recorded or viewed on a TV.
1. Selection and classification of CCD cameras
The CCD chip is like the human retina, which is the core of the camera. At present, China has no ability to manufacture. Most cameras on the market use chips made by Japanese companies such as SONY, SHARP, Panasonic, LG, etc. Now South Korea also has the ability to produce chips, but the quality is slightly inferior. Because the chips are produced in different grades and the manufacturers have different ways to obtain them, the CCD acquisition effect is also very different. At the time of purchase, you can take the following methods to detect: turn on the power, connect the video cable to the monitor, close the lens aperture, see if there are bright spots when the image is completely black, the snowflakes on the screen are not big, these are the most simple and direct detection of the CCD chip Method, and no other special instruments are needed. You can then open the iris to see a still life. If it is a color camera, it is best to take a brightly colored object to see if the image on the monitor is distorted, distorted, and whether the color or grayscale is smooth. A good CCD can restore the color of the scene well, making the object look clear and natural; and the image of the defective product will have a color cast phenomenon, even if it is facing a white paper, the image will show blue or red. Some CCDs will have impurities on the CCD target surface due to dust in the production workshop. In general, impurities will not affect the image, but in low light or microscopic photography, fine dust can also cause undesirable consequences. Such work must be carefully selected.
1. Divide the color camera according to the imaging color: it is suitable for identifying the details of the scene, such as the color of clothing or scene. Black and white camera: suitable for areas with insufficient light and areas where lighting equipment cannot be installed at night. When only monitoring the position or movement of the scene, a black and white camera can be used.
2. The image pixels with a resolution of less than 380,000 according to resolution sensitivity are general types. Among them, the products with 250,000 pixels (512 * 492) and resolution of 400 lines are the most common. High-resolution type with more than 380,000 image pixels.
3. According to the size of the CCD target surface, CCD chips have been developed in various sizes: Most of the chips currently used are 1/3 "and 1/4". When purchasing a camera, especially when there are strict requirements on the camera angle, the size of the CCD target surface, the cooperation between the CCD and the lens will directly affect the size of the field of view angle and the image clarity. 1 inch-the size of the target surface is 12.7mm wide * 9.6mm high, and the diagonal is 16mm. 2/3 inches-the target size is 8.8mm wide * 6.6mm high, and the diagonal is 11mm. 1/2 inch-target size is 6.4mm wide * 4.8mm high, 8mm diagonal. 1/3 inch-target size is 4.8mm wide * 3.6mm high, 6mm diagonal. 1/4 inch-the target size is 3.2mm wide * 2.4mm high, and the diagonal is 4mm.
4. Divide the PAL system according to the scanning system. NTSC system. China uses the interlaced scanning (PAL) system (black and white for CCIR), the standard is 625 lines, 50 fields, and only some non-standard systems are used in medical or other professional fields. In addition, Japan is NTSC, 525 lines, 60 fields (black and white is EIA).
5. According to the power supply, it is divided into 110VAC (the NTSC system is mostly of this type), 220VAC, 24VAC. 12VDC or 9VDC (mostly miniature cameras belong to this category).
6. Divide the internal synchronization according to the synchronization mode: use the synchronization signal generated by the synchronization signal generation circuit in the camera to complete the operation. External synchronization: An external synchronization signal generator is used to send the synchronization signal to the external synchronization input of the camera. Power synchronization (linear lock, line lock): Use the camera AC power to complete the vertical push synchronization. External VD synchronization: Input the VD synchronization pulse on the camera signal cable to complete the external VD synchronization. Multi-camera external synchronization: fixed external synchronization for multiple cameras, so that each camera can work under the same conditions, because each camera is synchronized, so even if one of the cameras is converted to other scenes, the synchronized camera's picture will not distortion.
7. According to the degree, CCD is divided into:
Illumination required for normal type normal work 1 ~ 3LUX
Illumination required for normal operation of moonlight type is about 0.1LUX. Illumination required for normal operation of starlight type is less than 0.01LUX. Infrared type is illuminated by infrared lamps, and imaging can be performed even when there is no light.
8. Divided by appearance: organic board type, pinhole type, hemispherical type.
The main technical indicators of CCD color camera
(1) CCD size, that is, the target surface of the camera. It was originally 1/2 inch, but now 1/3 inch has been popularized, and 1/4 inch and 1/5 inch have also been commercialized.
(2) The CCD pixel is the main performance index of the CCD. It determines the clarity of the displayed image. The higher the resolution, the better the performance of the image details. CCD is composed of area array photosensitive elements. Each element is called a pixel. The more pixels, the clearer the image. At present, most of the market is delimited by 250,000 and 380,000 pixels, and those with more than 380,000 pixels are high-definition cameras.
(3) Horizontal resolution. The typical resolution of a color camera is between 320 and 500 TV lines, mainly including 330 lines, 380 lines, 420 lines, 460 lines, 500 lines and other different grades. The resolution is expressed by TV lines (referred to as TV LINES), and the resolution of the color camera is between 330 and 500 lines. The resolution is related to the CCD and the lens, and is also directly related to the bandwidth of the camera circuit channel. Usually, the bandwidth of 1MHz is equivalent to a resolution of 80 lines. The wider the frequency band, the clearer the image, and the larger the line value.
(4) Minimum illumination, also called sensitivity. It is the sensitivity of the CCD to ambient light, or the darkest light required for normal CCD imaging. The unit of illuminance is LUX. The smaller the value, the less light is required and the more sensitive the camera. Moonlight-level and starlight-level high-sensitivity cameras can work in very dark conditions, 2 ~ 3lux is general illumination, and now there are ordinary cameras with less than 1lux.
(5) Scanning system. There are PAL system and NTSC system.
(6) Camera power supply. The AC has 220V, 110V, 24V, and the DC is 12V or 9V.
(7) Signal to noise ratio. The typical value is 46db. If it is 50db, the image has a small amount of noise, but the image quality is good; if it is 60db, the image quality is excellent without noise.
(8) Video output. Mostly 1Vp-p, 75Ω, all using BNC connectors.
(9) Lens installation method. There are C and CS methods, the difference between the two is that the photosensitive distance is different.
2. Adjustable function of CCD color camera
(1) Selection of synchronization method
A. For a single camera, the main synchronization methods are as follows:
Internal synchronization--using the crystal oscillation circuit inside the camera to generate a synchronization signal to complete the operation. External synchronization-use the synchronization signal generated by an external synchronization signal generator to send to the external synchronization input of the camera to achieve synchronization.
Power supply synchronization-also known as linear lock or line lock, is to use the AC power of the camera to complete the vertical push synchronization, that is, the camera and the power supply zero line synchronization.
B. For multi-camera systems, it is expected that all video input signals are vertically synchronized, so that when the camera output is converted, the picture distortion will not be caused, but the power supply of each camera in the multi-camera system may be taken from the three-phase power supply. Different phases, even the entire system is not synchronized with the AC power supply, the measures that can be taken at this time are: The synchronization signal generated by the same external synchronization signal generator is sent to the external synchronization input of each camera to adjust the synchronization. Adjust the "phase adjustment" potentiometer of each camera. Because the vertical synchronization of the camera is in phase with the positive zero crossing of the rising edge of the AC power when it is shipped from the factory, the phase delay circuit can make each camera have a different phase shift, thus To obtain proper vertical synchronization, the phase adjustment range is 0 ~ 360 degrees.
(2) Automatic gain control All cameras have a video amplifier that amplifies the signal from the CCD to a level that can be used. The amount of amplification is the gain, which is equivalent to having higher sensitivity, which can make it sensitive in low light, however The amplifier will be overloaded in a bright light environment, distorting the video signal. To this end, it is necessary to use the camera's automatic gain control (AGC) circuit to detect the level of the video signal, and switch the AGC in a timely manner, so that the camera can work in a larger illumination range, which is the dynamic range, that is, at low illumination Automatically increase the sensitivity of the camera, thereby increasing the strength of the image signal to obtain a clear image.
(3) Background light compensation Generally, the AGC working point of the camera is determined by averaging the contents of the entire field of view, but if the field of view contains a very bright background area and a very dark foreground target, then this time The determined AGC working point may not be suitable for the foreground target, and background light compensation may improve the display status of the foreground target. When the background light compensation is on, the camera only averages a sub-region of the entire field of view to determine its AGC working point. If the foreground target is in this sub-region, the visibility of the foreground target is expected to improve.
(4) In the CCD camera, the electronic shutter uses the charge accumulation time on the surface of the optical electronic control image to manipulate the shutter. The electronic shutter controls the accumulation time of the CCD of the camera. When the electronic shutter is closed, the accumulation time of the CCD for the NTSC camera is 1/60 seconds; for the PAL camera, it is 1/50 seconds. When the electronic shutter of the camera is opened, for the NTSC camera, the electronic shutter covers the range from 1/60 second to 1/10000 second in 261 steps; for the PAL type camera, the electronic shutter covers the 1/50 second in 311 steps. To the 1/10000 second range. When the electronic shutter speed increases, the light focused on the CCD decreases within the time allowed for each video field, which will reduce the sensitivity of the camera. However, a higher shutter speed will produce a "pause" for observing moving images. 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 realize the camera image can accurately reflect the scene. There are two methods of manual white balance and automatic white balance.
A. Automatic white balance continuous mode-At this time, the white balance setting will be continuously adjusted with the change of the color temperature of the scene, the range is 2800 ~ 6000K. This method is most suitable for the scene where the color temperature of the scene changes continuously during shooting, so that the color expression is natural, but for the scene with little or no white, continuous white balance can not produce the best color effect. Button mode-first point the camera to a white target such as white wall, white paper, etc., then set the automatic mode switch from manual to the setting position, keep it in this position for a few seconds or until the image appears white, the white balance is executed After that, turn the automatic mode switch back to the manual position to lock the white balance setting. At this time, the white balance setting will remain in the camera's memory until it is changed again. The range is 2300 ~ 10000K. During this period, even This setting will not be lost when the camera is powered off. It is the most accurate and reliable to set the white balance with the button, which is suitable for most applications.
B. Manual white balance is turned on. Manual white balance will turn off automatic white balance. At this time, there are up to 107 levels for adjusting the red or blue state of the image. For example, increase or decrease the red one level, increase or decrease the blue one grade. In addition to times, some cameras also have commands to fix white balance at 3200K (incandescent lamp level) and 5500K (daylight level).
(6) For most applications, color adjustment is not required for the camera. If adjustment is required, careful adjustment is required to avoid affecting other colors. Adjustable color methods are: red-yellow color increases, then red Move one step toward magenta. The red-yellow color is reduced, and now the red is moved one step toward yellow. The blue-yellow color increases, and at this time the blue color is moved one step toward the blue-blue color. The blue-yellow color is reduced, and the blue is moved one step toward magenta.
3. Digital adjustment control method
The new camera adopts digital adjustment control for the adjustment of the aforementioned optional parameters. At this time, it is not necessary to manually adjust the potentiometer but the auxiliary control code is used, and these adjustment parameters are stored in the digital memory unit, increasing stability and reliability .
DSP camera introduces some digital processing technology on the basis of analog system, called digital signal processing (DSP, DIGITAL SIGNAL PROCESSOR) camera. This kind of camera has the following advantages:
1. Due to the use of digital detection and digital computing technology, it has an intelligent background light compensation function. Conventional cameras require that the subject to be photographed be placed in the center of the screen and occupy a larger area to have better background light compensation, otherwise too bright background light may reduce the transparency of the center of the image. The DSP camera divides a picture into 48 small processing areas to effectively detect the target, so that even small, thin or not in the center of the picture can be clearly presented.
2. Due to DSP technology, it can automatically track white balance, that is, it can detect and track "white" under any conditions, and reproduce the original color with digital operation processing function. Traditional cameras average all the colors on the screen, so if the color objects occupy a large area on the screen, the color reproduction will be unbalanced, that is, the original colors cannot be reproduced. The DSP camera divides a picture into 48 small processing areas, so that it can effectively detect white. Even if there is only a small piece of white on the picture, the camera can track it to reproduce the original color. When shooting grid-like objects, image aliasing caused by camera color noise can be minimized. The difference between the C and CS interfaces is the distance between the contact surface of the lens and the camera to the focal plane of the lens (where the camera CCD photoelectric sensor should be). The distance of the C-type interface is 17.5mm., The distance of the CS-type interface is 12.5mm. . C type lens and C type camera, CS type lens and CS type camera can be used together. A 5mm C / CS adapter ring can be used between the C-type lens and the CS-type camera. CS type lens and C type camera cannot be used together.
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