Introduction of monitoring camera parameters

The monitoring camera is used to shoot the monitoring area and convert it into an electrical signal. According to the specifications, it can be divided into 1/3 ",1/2" and 2/3 ",and the installation methods are fixed and desktop with cloud.

CCD (CMOS) size, that is, the camera target surface. The original 1/2 inch and 1/3 inch have been popularized, and 1/4 inch and 1/5 inch have also been commercialized.

The pixel of CCD (CMOS) is the main performance index of CCD(CMOS), which determines the clarity of the displayed image. The higher the resolution, the better the image details. CCD consists of array photosensitive elements, and each element is called a pixel. The more pixels, the clearer the image. Most markets are demarcated by 250,000 and 380,000 pixels. More than 380,000 pixels are high-definition cameras.

Horizontal resolution. The typical resolution of color camera is between 320 and 500 TV lines, mainly including 330 lines, 380 lines, 420 lines, 460 lines and 500 lines. The resolution is expressed by TV lines, and the resolution of color camera is between 330 lines and 500 lines. Resolution is related to CCD and lens, and also directly related to the frequency band width of camera circuit channel. Usually, the bandwidth of 1MHz is equivalent to the resolution of 80 lines. The wider the frequency band, the clearer the image and the larger the line value.

Minimum illumination, also known as sensitivity. It is the sensitivity of CCD(CMOS) to ambient light, or the darkest light required for normal imaging of CCD. The unit of illumination is lux. The smaller the value, the less light is needed and the more sensitive the camera is. High-sensitivity cameras such as moonlight camera (about 0. 1Lux) and starlight camera (below 0.0 1Lux) can work in very dark conditions, and 2~3Lux is the general illumination.

Scanning system. There are PAL system and NTSC system.

China adopts interlaced scanning (PAL) system (black and white CCIR), and the standard is 625 lines and 50 fields. Only medical or other professional fields use some non-standard systems. Japan adopts NTSC system with 525 lines and 60 games (EIA black and white).

Camera power supply. Ac power supply is 220V, 1 10V, 24V, and DC power supply is 12V or 9V.

Signal to noise ratio. The so-called signal-to-noise ratio refers to the ratio of signal voltage to noise voltage, which is usually expressed by S/N.

When the camera shoots a bright scene, the picture displayed by the monitor is usually bright, and it is difficult for observers to see the interference noise in the picture; When the camera shoots a dark scene, the picture displayed by the monitor is dim, and the observer can easily see the snowflake-like interference noise in the picture at this time. The intensity of interference noise (that is, the influence of interference noise on the picture) is directly related to the signal-to-noise ratio of the camera, that is, the higher the signal-to-noise ratio of the camera, the smaller the influence of interference noise on the picture.

Generally speaking, the signal voltage is much higher than the noise voltage, and the proportion is very large. Therefore, the actual calculation of the signal-to-noise ratio of the camera usually takes the logarithm of the ratio of the mean square of signal voltage to the mean square of noise voltage, taking 10 as the base and multiplying it by the coefficient of 20. The typical value is 46db. If it is 50db, the image is a little noisy, but the image quality is good; If it is 60db, the picture quality is excellent and there is no noise.

Generally, the signal-to-noise ratio (SNR) values given by cameras are the values when AGC (Automatic Gain Control) is turned off, because when AGC is turned on, small signals will be enhanced, so the noise level will be improved accordingly.

Video output. Most of them are 1Vp-p and 75 Ω, using BNC connectors.

Installation method of lens. There are two modes, C and CS, the difference lies in the different photosensitive distance. (1) AGC on/off (automatic gain control)

There is a video amplifier in the camera, which amplifies the signal from CCD to a usable level. Its magnification is gain, which is equivalent to high sensitivity. However, in bright lighting environment, the amplifier will be overloaded, which will distort the video signal. When the switch is turned on, the lens aperture is completely opened in the case of low brightness, which automatically increases the gain and obtains a clear image. When the switch is closed, natural and low-noise images can be obtained at low brightness.

(2) Automatic white balance on/off (automatic white balance)

When the switch is turned on, the characteristic/color temperature of the light source is detected through the lens, so that the white level can be set automatically and continuously, and the gains of red and blue signals can be controlled even if the characteristic/color temperature changes.

③ALC/ELC (automatic brightness control/electronic brightness control)

When ELC is selected, the electronic shutter will automatically and continuously change the exposure time of CCD image sensor according to the brightness of incident light (generally, it will be continuously adjusted from110000 seconds). When this method is selected, ALC automatic aperture lens can be replaced by fixed or manual aperture lens.

It should be noted that in outdoor or bright environment, ALC lens should be selected because of the limited control range of ELC; Under some unique lighting conditions, the following situations may occur:

(1) There is a strong tailing or blurring phenomenon on high-brightness objects such as spotlights or windows.

(2) The image is obviously flickering, and the color reproducibility is unstable.

(3) The white balance changes periodically. If these phenomena occur, ALC lens should be used.

When using the ELC method with a fixed aperture lens, the depth of field of the image may be smaller than that obtained by using the ALC lens. Therefore, when the camera fully opens the fixed aperture lens and adopts ELC mode. The depth of field will be smaller than when using ALC lens, and distant objects in the image may not be in focus.

When the lens is an automatic aperture lens, you need to turn the switch to ALC mode.

(4)BLC ON/OFF (backlight compensation switch)

When powerful and useless background lighting affects the clarity of important objects in the middle, the switch should be turned to the ON position. Note: ① When it is used in cONjunction with the pan/tilt or the light changes rapidly, it is recommended to turn the switch to the OFF position, because when it is in the on position, the aperture speed of the lens will slow down; ② If the desired object is not in the middle of the image, the backlight compensation may not fully play its role.

(5)LL/INT (synchronous selector switch)

This switch is used to select the camera synchronization mode, and INT is internal synchronization; LL is power synchronization. Some cameras also have an LL phase power synchronous phase controller. When the camera is used in the power synchronization state, the device can adjust the phase of the video output signal by about one frame. (Adjustment requires professionals)

(6) Video /DC (lens control signal selector switch)

There are two kinds of control signals for ALC automatic aperture lens. When it is necessary to install an automatic aperture lens with DC control signal on the camera, the DC position should be selected, and when it is necessary to install an automatic aperture lens with video control signal, the video position should be selected.

When ALC auto-stop video drive lens is selected, it may be necessary to adjust the video level L/H. The controller adjusts the control level output to the automatic aperture lens to control the opening and closing of the lens aperture (concave light).

In the camera accessories, there is a small black plug with four pins connected to the black socket on the camera. If you are using an automatic aperture lens driven by DC, the plug is already on the lens. Just plug it in the socket and turn the selector switch to DC. If you use a video-driven automatic aperture lens, you need to weld it with a soldering iron according to the instructions. Due to the different definitions of manufacturers, the welding methods are also different, so please pay attention when installing.

(7) Soft/clear (LOD selector switch)

This switch is used to adjust whether the output image is clear or soft, and is usually set in a clear position at the factory.

(8) No flicker (no flicker mode)

When the power frequency is 50Hz, the CCD accumulation time is 1/50s. If the NISC camera is used, its vertical synchronization frequency is 60Hz, which will cause the visual image on the monitor to be unsynchronized and flicker. On the contrary, PAL cameras will also have this image when the power supply is 60Hz. In order to overcome this phenomenon, a flicker-free mode file is set in the electronic shutter, which provides1100 seconds for the NISC camera and1120 seconds for the PAL camera, which can prevent the picture from flickering on the display. Manual electronic shutter: Some users use CCD to shoot fast moving objects. If they shoot at the speed of 1/50 seconds, they will produce a trailing image, which will seriously affect the image quality. Some cameras provide manual electronic shutter to fix the charge coupling speed of CCD at a certain value, such as 1/500,11000, 1/2000 seconds, etc. At this time, the charge coupling speed of CCD is accelerated, which will relatively reduce the trailing image of the collected image, and is also very useful for observing high-speed movement or electric spark. Therefore, some special cameras provide manual electronic shutters for users with special purposes. With the increasing popularity of surveillance systems in commercial and civil fields, surveillance cameras (surveillance cameras) are widely used in various fields to protect social security. Video surveillance cameras are widely used in residential buildings, real estate villas, shopping malls and shops, financial offices and so on. Every different application field needs different types of surveillance cameras, and the camera gun is one of them. According to different applications, the following mainly explains the control and process of monitoring camera in digital film shooting:

1. Monitor controls exposure.

First, adjust the monitor to a relatively standard state, and adjust this state at any time during shooting. The high-definition monitor has a waveform diagram, which is of great practical significance for controlling exposure and distinguishing the details of light and dark parts.

2. Automatic aperture control exposure

At this time, the automatic aperture is used as an exposure instrument, and the photographer should have a particularly clear understanding of the dynamic range curve of the monitoring camera.

3. zebra crossing control exposure

A zebra crossing is usually designated with an amplitude of 90%-95% of the signal level. The high-definition surveillance camera is designed with two zebra stripes. The first stage is set to 70%, that is, the amplitude of 700 mV video signal level is 60%-65%. The other is 100% zebra crossing, in which 70% corresponds to the gray area in the image, and 100% is the bright part.

According to statistics, in 2006, the number of films shot by digital equipment reached 1 10, accounting for 1/3 of the national total output. The technical difference between digital film and film film in actual shooting is mainly the control of tone, color and exposure, and the shooting process is also different.

The exposure of digital movies. Lens-spectroscope -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-black cutting. Film movies are controlled by exposure meters. Some photographers also use digital exposure instruments. Generally speaking, the sensitivity of digital cameras is equivalent. For SONYF3200K, the exposure of digital movies is controlled by. Shutter 1/48 seconds, 24P mode, equivalent to 320 degrees. Exposure meter is rarely used in digital movies because it is set by exposure meter according to the photosensitive characteristics of film emulsion. Film is sensitive to blue light and ultraviolet light, while digital is relatively sensitive to red light.

Video surveillance camera. This product has the characteristics of clear image, bright color, high number of lines and low illumination. With the continuous investment in technology research and development, the surveillance camera will promote the market innovation process with the growth of its CCD technology and image sensor solution lineup. A camera is a device for image decomposition and photoelectric signal conversion. Image decomposition is the process of decomposing a complete image into several independent pixels (the smallest unit of TV image). Generally speaking, the more pixels, the clearer the image. Each pixel is represented by a single color and brightness. The camera can convert the optical signal of each pixel in the image into a corresponding electrical signal, and then transmit it to the output terminal in a certain order. Camera devices are divided into camera tubes and solid-state (semiconductor) camera devices.

① Camera tube and electron beam device are divided into image analysis tube, photomultiplier tube, super-positive image analysis tube and photoconductive camera tube. Miniature lead oxide photoelectric camera tube is often used in new cameras. All kinds of camera tubes have a vacuum glass shell with a target surface and an electron gun inside. The shot scene is imaged on the target surface through the window controlled by the automatic aperture on the glass shell. By using the photoelectric emission effect or photoconductive effect of the target surface, the illumination distribution of each point on the target surface is converted into the corresponding potential distribution, and the light image is turned into an electric 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 turn.

② Solid-state imaging devices. A new type of charge coupled device. Hundreds of thousands of device units are arranged in an array, and the surface layer has photosensitive characteristics. The shot scene is imaged on the front, and the amount of charge stored in each unit is proportional to the illumination. By using the clock pulse and shift control signal, the signals of the previous units are shifted out in a certain order, and the image electrical signal whose intensity changes with time can be obtained.

The preamplifier is a video amplifier, which amplifies the weak signal output by the camera equipment to a specified amplitude. In order to ensure a good signal-to-noise ratio, the noise figure of the preamplifier is required to be as small as possible. Testing the monitoring camera mainly tests the clarity and color reproduction, illumination and backlight compensation, followed by measuring the distortion, power consumption and minimum working voltage of the monitoring camera. Firstly, the measurement steps of clarity and color reproduction, illumination and backlight compensation are introduced.

1. Measurement of transparency:

When testing multiple surveillance cameras, the same lens (fixed focus and two variable lenses are recommended) should be used, and the given scale lines *** 10 vertical lines and 10 horizontal lines should be clearly and accurately counted according to the central circle of the test card appearing on the left and right sides of the surveillance screen. Represents vertical definition and horizontal definition respectively, and the corresponding groups have given the number of lines. Such as vertical 350 lines and horizontal 800 lines, it is best to use black and white display at this time. When testing, you can focus on the distant scene, or you can focus while measuring. It's better to use both, and you can see the difference (convergence) of this camera.

2. Color reduction test:

The color monitor that should be selected when testing this parameter. First, observe people and clothes from a distance to see if there is any color distortion, compare brightly colored objects, and see the response sensitivity of the monitoring camera. Put the color picture album in front of the surveillance camera to see if the outline of the picture is clear, too light or too thick. Shoot the moving color object again to see if there is any color difference tailing, delay and blur. The test conditions are as follows: When the first generation illumination of the camera is 50V, it should be measured at the illumination of 50+ 10V, that is, 10V is added to the first generation illumination of the surveillance camera, and the aperture should be kept in the closest state.

3. Illuminance:

The surveillance camera is placed in the darkroom, with active 220V self-lighting lights and voltage regulators in front and behind the darkroom. The voltage regulator adjusts the brightness of the lamp in the darkroom. The voltage can be adjusted from 0V to 250V, and the indoor lighting can also be adjusted from the darkest to the brightest. During the test, record a minimum illuminance value when the aperture of the camera is opened to the maximum (dim the movable light with the voltage regulator until the built-in picture in the darkroom can't be seen clearly), then record the next minimum illuminance value when the aperture is adjusted to the minimum, or adjust and turn off the front and rear lights respectively.

4. Backlight compensation:

There are two ways to test this parameter: one is to turn on the voltage-regulating lamp in front of the camera in the darkroom and turn it to the brightest, then put a picture or text under the lamp, shoot the surveillance camera to see if the picture and text can be seen clearly, and adjust the AL and AX shift switches to see if there is any change, which is the best. The other is to shoot the camera out of the window in sunny conditions to see if you can see the images and words clearly at this time.

5. Monitor camera distortion:

Look at the distortion of the surveillance camera. Put the test card in front of the camera to make the whole sphere appear on the screen, see if there is an ellipse in the circular sphere, move the camera forward to see if there is magnification at the center of the circle, and then test the corners and borders for arc distortion at a distance.

6. Power consumption:

Minimum working voltage, measure current with multimeter, and adjust voltage with small voltage regulator.

In the security system, the image mainly comes from CCD camera, which is called Charge Coupled Device for short. It can convert light into charge, store and transfer the charge, and also take out the stored charge to change the voltage, so it is an ideal camera element. The CCD camera composed of it is widely used because of its small size, light weight, no influence of magnetic field, vibration and impact resistance.