Surveillance camera's role is to monitor the area of the camera and convert it into an electrical signal, according to the specifications can be divided into 1/3 ″, 1/2 ″ and 2/3 ″ and other types, the installation mode has a fixed and with the PTZ two kinds.
- CCD (CMOS) size, that is, the camera target surface. The original more than 1/2 inch, 1/3 inch has been popularized, 1/4 inch and 1/5 inch has also been commercialized.
- CCD (CMOS) pixels, CCD (CMOS) is the main performance indicator, which determines the degree of clarity of the displayed image, the higher the resolution, the better the performance of the image details.CCD is composed of a surface array of light-sensitive elements, each element is called a pixel, the more pixels, the clearer the image. Most of the market is demarcated by 250,000 and 380,000 pixels. 380,000 pixels and above are high definition cameras.
- Horizontal resolution. The typical resolution of a color camera is between 320 and 500 TV lines, mainly 330 lines, 380 lines, 420 lines, 460 lines, 500 lines and other different grades. The resolution is expressed in terms of TV lines (abbreviated as TV LINES), and the resolution of color cameras 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.
- Minimum illumination, also known as sensitivity. It is the degree of sensitivity of the CCD (CMOS) to ambient light, or the darkest light required for normal CCD imaging. The unit of illumination is Lux (Lux), the smaller the value, indicating that less light is needed, the more sensitive the camera. Moonlight level (0.1Lux or so) and starlight pole (0.01Lux or less) and other high sensitivity cameras can work in very dark conditions, 2 ~ 3Lux is a general illumination.
- Scanning system. There are PAL and NTSC system.
China uses 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. Japan for NTSC, 525 lines, 60 fields (black and white for EIA)
- Camera power supply. AC 220V, 110V, 24V, DC 12V or 9V.
- Signal-to-noise ratio. The so-called signal-to-noise ratio refers to the ratio of the signal voltage to the noise voltage, which is usually expressed by S/N.
When the camera takes a brighter scene, the monitor display screen is usually brighter, the observer is not easy to see the interference noise in the screen; and when the camera takes a darker scene, the monitor display screen is dimmer, the observer is easy to see the snowflake interference noise in the screen. The strength of the interference noise (that is, the degree of influence of the interference noise on the screen) and the camera signal-to-noise ratio index is directly related to the good and bad, that is, the higher the signal-to-noise ratio of the camera, the smaller the impact of the interference noise on the screen.
As a result of the general situation, the signal voltage is much higher than the noise voltage, the ratio is very large, therefore, the actual calculation of the size of the camera signal-to-noise ratio is usually the ratio of the mean-square signal voltage and the mean-square noise voltage is taken to the bottom of the logarithm of the 10 and then multiplied by the coefficient of 20. typical value of 46db. If 50db, there is a small amount of noise in the image, but the image quality is good; if 60db, the image quality is excellent, there is no noise. Image quality is excellent, no noise.
The signal-to-noise ratio values given by the camera are generally when the AGC (Automatic Gain Control) is off, because when the AGC is on, it boosts the small signals, which raises the noise level accordingly.
- Video output. Mostly 1Vp-p, 75Ω, all with BNC connectors.
- Lens mounting. There are C and CS mode, the difference between the two is that the light-sensitive distance is different. (1) AGC ON/OFF (Automatic Gain Control)
The camera contains a video amplifier that amplifies the signal from the CCD to a usable level, and its amplification, i.e., gain, is equivalent to having a high sensitivity, however, the amplifier will be overloaded in a brightly illuminated environment, distorting the video signal. When the switch is ON, the lens aperture is fully opened under low-light conditions and the gain is automatically increased to obtain a clear image. When the switch is OFF, a natural and low-noise image is obtained at low brightness.
(2) AWB ON/OFF (Auto White Balance)
When the switch is toggled ON, the characteristic/color temperature of the light source is detected through the lens to automatically and continuously set the white level, and the gain of the red and blue signals is controlled even when the characteristic/color temperature changes.
(3) ALC/ELC (Automatic Luminance Control/Electronic Luminance Control)
When ELC is selected, the electronic shutter continuously and automatically varies the exposure time of the CCD image sensor according to the luminance of the incoming light (generally adjusted continuously from 1/50 to 1/10,000 second). When this is selected, a fixed or manual iris lens can be used in place of the ALC auto iris lens.
Note: In outdoor or bright environments, ALC-style lenses should still be selected due to the limited range of ELC control; under certain unique lighting conditions, the following may occur:
(1) Strong trailing or blurring on high-brightness objects such as spotlights or windows.
(2) Significant image flicker and erratic color reproduction.
(3) Periodic variations in white balance, if these phenomena occur, ALC lenses should be used.
When using the ELC method with a fixed aperture lens, the depth of field of the image may be less than that obtained with an ALC-style lens. Therefore, the camera is fully opened with the fixed-aperture lens and when the ELC method is used. The depth of field will be smaller than when using an ALC-style lens, and distant objects on the image may not be in focus.
When the lens is an auto iris lens, the switch needs to be flipped to the ALC method.
(4) BLC ON/OFF (BACKLIGHT COMPENSATION SWITCH)
The switch should be flicked to the ON position when strong and useless background illumination affects the sharpness of important objects in the center. Note: ① It is recommended that this switch be placed in the OFF position when used with a gimbal or when the illumination changes rapidly, as the lens aperture slows down in the ON position; ② Backlight compensation may not be fully effective when the desired object is not in the center of the image.
(5)LL/INT (Sync Selector Switch)
This switch is used to select the camera synchronization method, INT for internal synchronization; LL for power synchronization. Some cameras also have a LL PHASE power synchronization phase controller. When the camera is used in the power synchronization state, this device can adjust the phase of the video output signal, the adjustment range is about one frame. (Adjustment needs to be carried out by professionals)
(6) VIDEO/DC (Lens Control Signal Selection Switch)
There are two kinds of control signals for ALC auto iris lenses, DC position should be selected when auto iris lenses with DC control signals are required to be mounted on the camera, and VIDEO position should be selected when auto iris lenses with video control signals are required to be mounted. position.
When an ALC auto iris video drive lens is selected, there will also be a video level control (VIDEO LEVEL L/H) that may need to be adjusted, which regulates the control level output to the auto iris lens for controlling the lens iris to open wide and close (concave in light).
Among the camera's accessories is a small black plug with four pins that connects to a black socket on the camera. If you use a DC-driven auto iris lens, the plug is already made on the lens, just plug it into the socket and turn the selector switch to DC; if you use a video-driven auto iris lens, you need to solder it with a soldering iron by the user according to the instruction manual's labeling. Because of the different definitions of manufacturers, so the soldering method is also different, please pay attention to the installation.
(7)SOFT/SHARP (detail level selector switch)
This switch is used to adjust whether the output image is clear (SHARP) or smooth (SOFT), and is usually factory set at the SHARP position.
(8) FLICKERLESS (no flicker mode)
In the area of power frequency of 50Hz, the CCD accumulation time of 1/50 seconds, if you use the NISC camera, the vertical synchronization frequency of 60Hz, which will cause the visual image is not synchronized, flicker in the monitor; on the contrary, in the area of the power supply of 60Hz with the On the other hand, PAL cameras in areas where the power supply is 60 Hz will also have this phenomenon. In order to overcome this phenomenon, the electronic shutter set up a non-flicker mode gear, the NISC camera to provide 1/100 seconds, the PAL camera to provide a fixed shutter speed of 1/120 seconds, you can prevent the image on the monitor flicker. Manual electronic shutter: Some users use CCD to take pictures of fast-moving objects, and if you shoot at 1/50 second, it will produce a trailing image, which will seriously affect the image quality. Some cameras give a manual electronic shutter, so that the CCD charge coupling speed is fixed at a certain value, such as 1/500, 1/1000, 1/2000 seconds, etc., at this time, the charge coupling speed of the CCD to improve the image captured in this way, relatively speaking, will reduce the trailing image, and for the observation of high-speed movement or sparks of a class of objects that must be used in this setting. Therefore, some specialized cameras give a manual electronic shutter, available to special-purpose users. With the growing popularity of surveillance systems in commercial and civil use, surveillance cameras (surveillance cameras) are widely used in various fields to protect social security. Video surveillance cameras are widely used in residential homes, buildings and villas, shopping malls and stores, and financial offices. Each different application requires a different type of surveillance camera, camera gun is one of them. According to the different applications of the following is mainly explained on the surveillance camera in the digital movie shooting control and process:
1. monitor control storm light
First of all, the monitor is adjusted to a relatively standard state, and to be in the shooting at any time to adjust the state of this, high-definition monitors have a waveform, for the control of the storm light to distinguish between bright and dark parts of the details is very meaningful.
2. Auto iris control storm light
This is the use of auto iris as a light meter, the photographer has to monitor the dynamic range curve of the camera to have a particularly clear understanding.
3. Zebra control storm light
Zebra is usually specified in the signal level of 90% -95% of the amplitude. High-definition surveillance cameras are designed with two levels of zebra stripes. A level set at 70% that is, 700 mV video signal level amplitude 60%-65%, <basically yellow skin reflectivity 23% of the corresponding video signal level value >. The other is 100% zebra, 70% corresponds to the gray area in the image, 100% for the bright part.
According to statistics, in 2006, the number of films shot by digital equipment reached 110, accounting for the country's total output of 1/3. The technical differences between digital films and film films in the actual shooting are mainly the shadow \ hue \ storm light control and many other different, shooting process is also different.
Digital movie exposure link. Lens - spectral filter - CCD - A/D analog-to-digital conversion - black spot correction - gain adjustment - white balance - stray light correction -Detail Adjustment - Color Giant Array - Inflection Point Adjustment - GMA Adjustment - White Cut Black Cut. In film, the exposure is controlled by a light meter. Some cinematographers also use a light meter in digital. Generally, digital cameras have equivalent sensitivity to light, for SONYF900, in 3200K color temperature, shutter 1/48 seconds, 24P mode, equivalent to 320 degrees. In digital cinema is rarely used in the light meter, because the light meter for the film emulsion light-sensitive properties of the settings. Unlike film, which is sensitive to blue and ultraviolet light, digital is relatively sensitive to red light.
Video surveillance cameras. The product has a clear image, color fidelity, high line count, low illumination and other characteristics. Technology research and development continues to invest in surveillance cameras will drive the process of innovation in the market with the growth of its lineup of CCD technology and image sensor solutions. Camera to complete the image decomposition and photoelectric signal conversion devices. Image decomposition is the process of breaking down a complete image into a number of independent pixels (the smallest unit that makes up the TV picture frame). Generally speaking, the greater the number of pixels, the clearer the image. Each pixel is represented by a single color and brightness. The camera device converts the optical signals of each pixel in the image into corresponding electrical signals, which are then transmitted to the output in a certain order. Camera devices are divided into two categories: camera tubes and solid-state (semiconductor) camera devices.
①Camera tube, electron beam devices, but also divided into the analysis of the tube, photomultiplier analysis of the tube, ultra-positive analysis of the tube and photoconductive camera tube and several other kinds. New cameras use more compact lead oxide photoelectric camera tube. A variety of camera tubes have a vacuum glass shell, which is equipped with a target surface and electron gun. Be ingested scene through the glass shell on the automatic aperture control storm window imaging in the target surface, the use of the target surface of the photoelectric emission effect or photoconductive effect of the target surface of the illumination distribution of the points into the corresponding potential distribution, the optical image into an electrical image. Driven by the deflection coil outside the tube, the electron beam scans the target surface point by point and line by line, and outputs the potential signals of each pixel on the scanning path in sequence.
②Solid-state camera device. A new type of charge-coupled device (CCD). Hundreds of thousands of device units arranged in an array, the surface layer has photosensitive properties. The scene being photographed in the array, each unit of storage charge and illumination is proportional. The use of clock pulses and shift control signals, the array surface of the unit signals in a certain order to move out, you can get the intensity of the image of the time-varying electrical signals.
Preamplifier The weak signal output from the camera device is amplified to a specified amplitude of the video amplifier. In order to ensure a good signal-to-noise ratio, the preamplifier is required to have the smallest possible noise factor. Testing surveillance cameras mainly test clarity and color reproduction, illumination, backlight compensation, followed by the measurement of its surveillance camera distortion, power consumption, minimum operating voltage, the following first clarity and color reproduction and illumination, backlight compensation measurement steps first introduced.
1. Sharpness Measurement:
Multiple surveillance cameras for testing, the same lens should be used, (recommended for fixed-focus, two variable lenses), to test the card center circle appeared in the monitor screen on the left and right side of the shall be clearly and accurately counted has been given to the scale line *** 10 groups of vertical lines and 10 groups of horizontal lines. Represent the vertical clarity and horizontal clarity, and the corresponding group has been given the number of lines. Such as vertical 350 lines horizontal 800 lines, it is best to use a black and white monitor. Tests can be in the distant object focus, can also be measured while focusing. It is best to use both, you can see the difference between this camera (for near and far convergence).
2. Color reproduction test:
The test of this parameter should choose a good color monitor. First of all, long-distance observation of people, clothing, to see if there is no color distortion, take a brightly colored object comparison, to see the monitoring camera response sensitivity, take a color album placed in front of the monitoring camera, to see the picture is outlined clearly, too light or too thick, and again should be the movement of color objects for the camera to see if there is any color trailing, lag, blurring, and so on. Test conditions so that the camera most generation of illumination in the 50V should be measured in 50 + 10V illumination, that is, each surveillance camera most generation of illumination based on the addition of ten volts, and the aperture should be kept closest to the state.
3. Illumination:
Surveillance cameras in the darkroom, darkroom before and after the active 220V incandescent lamps, set up a regulator at the regulator to adjust the voltage to regulate the dark room lights dark, the voltage can be adjusted from 0V to 250V. Indoor lighting can also be adjusted from the darkest to the brightest, test the camera aperture are open to the maximum record the next minimum illumination value (the active lights with a voltage regulator to darken the dark room built-in picture) and then the aperture to the minimum and then record the next minimum illumination value, but also before and after the lights were regulating the pressure of light and darkness.
4. Backlight Compensation:
Test this parameter there are two ways: one is in the dark room, the camera front side of the regulator lights open, adjusted to the brightest, and then in the light of the bottom of the placement of a picture or text, the surveillance camera to meet the light camera to see whether the image and text can be seen clearly, the screen is not harsh, and adjust the AL, AX pull the switch to see if there is any change, which has the best results. Another is in the sunny situation to the camera to the window, this time to see the image and text can be seen clearly.
5. Surveillance camera distortion:
See the surveillance camera distortion put the test card on the front of the camera so that the whole sphere appears on the screen, look at the sphere with or without ellipse, move the camera forward, look at the center of the circle with or without magnification, and then test the sides, corners, frames from a distance, such as the presence of arc distortion.
6. Power consumption:
Minimum operating voltage, use a multimeter to measure the current, use a small voltage regulator to adjust the voltage to see
Security systems, image generation is currently mainly from the CCD camera, the CCD is a charge-coupled device (charge coupled deice) for short, which can change the light into a charge and charge storage and transfer, but also the storage of the charge out to make the voltage occur. Stored charge out to make the voltage change, so it is the ideal camera components to its composition of the CCD camera has a small size, light weight, not affected by magnetic fields, with anti-vibration and impact characteristics and is widely used.