The so-called gun camera is only for the appearance of distinction, this is the camera's initial form, in fact, the camera board + housing, without the lens, can freely match various models of the lens. Mounting methods can be used for hoisting or wall mounting. Outdoor installations are generally equipped with protective covers. Currently, these cameras are mainly used in special fields and high-end fields. The middle and low-end areas are basically replaced by one-piece machines and hemispheres. The gun type is mainly suitable for areas where lighting is not sufficient and where lighting equipment cannot be installed at night. A gun camera may be used when monitoring the position or movement of the scene. Gun-type cameras have a wider range of applications. According to the choice of lenses, remote monitoring or wide-angle monitoring can be realized. The application occasions are also wider than the hemisphere. The zoom range of the guns depends on the lens used, and can be several times Dozens of times, and the replacement of the lens easier, in addition to the need for a bolt if you need to configure the protective cover.
Basic function analysis 1. The number of pixels
The number of pixels refers to the maximum number of pixels of the gun camera CCD sensor, and some of them give the number of pixels in the horizontal and vertical directions, such as 500H× 582V, and some give the waited product values ​​of the first two, such as 300,000 pixels. For a CCD chip of a certain size, the larger the number of pixels, the smaller the area of ​​each pixel unit, and the higher the resolution of a gun camera composed of the chip.
2. Resolution
Resolution is an important parameter to measure the advantages and disadvantages of black and white gun cameras. It means that when a gun camera takes equally spaced black and white stripes, it can be seen on a monitor (which should have a higher resolution than the camera). When the number of lines exceeds this number, only a grayed-out screen can be seen and black and white lines can no longer be distinguished.
The resolution test usually uses a gun camera to capture a resolution test card and read the data through a waveform monitor. The specific method is as follows:
(1) Arrange the test environment. Place the resolution test card on the standard test light box, about 3m away from the camera. The video output of the gun camera is connected to a waveform monitor and the output of the waveform monitor is connected to a high resolution black and white monitor.
(2) The illuminance of scenery is set to 2000lx, and the color temperature of the light source is set to 3200K.
(3) Adjust the lens focal length (or select the appropriate fixed-focus lens and move the camera forward or backward slightly) to fill the monitor screen with the image of the resolution card and sharpen the image with precise focusing.
(4) Observe the resolution card with the selected oscilloscope to get the waveform.
(5) Adjust the lens aperture so that the signal white level reaches 100% (70mV). At this time, the number of TV lines whose modulation is deeper than 5% is the limit resolution.
3. Minimum illumination
The minimum illumination is also an important parameter to measure the merits of the gun camera. Sometimes the word “lowest†is omitted and it is simply referred to as “illuminanceâ€. The minimum illuminance is a luminosity value of the scene when the illuminance of the subject is low to a certain extent and the level of the video signal output by the gun camera is as low as a predetermined value. When measuring this parameter, the maximum relative aperture of the lens should also be specified. For example, with an F1.2 lens, when the brightness of the subject is as low as 0.04LX, the amplitude of the video signal output by the camera is 50% of the maximum amplitude, ie, 350mV (the maximum amplitude of the standard video signal is 700mV. ), the minimum illumination of this gun camera is called 0.04LUX/F1.2. The brightness value of the subject was low, and the amplitude of the video signal output by the gun camera was less than 350mV. Reflected on the screen of the monitor, it would be a gray image with a hardly distinguishable level.
At present, due to the fact that the market's specifications are not yet uniform, the low illumination characteristics of some gun cameras with low illumination indices may not be as good as the low illumination characteristics of gun cameras with slightly higher illumination indexes. The reason for this is that the standards used in the measurement of low-lightness indicators are different. Still taking the above example as an example, if the amplitude of the video signal output by the camera is reduced to 30% of the maximum amplitude (that is, 210mV) as a reference, the brightness value of the imaged object can be further lowered, such as 0.03LX, If the optical lens is further replaced by an F1.0 lens, the brightness of the subject can be further reduced due to the increase of the luminous flux, such as 0.02LX.
It can be seen from the above analysis that it is impossible to accurately determine which camera has low illuminance characteristics by putting aside the measurement standard and simply comparing the illuminance nominal value of a certain brand of gun camera with the illuminance nominal value of another brand of gun camera. Good conclusions, because the relative aperture of the lens they use and the specified value of the output video signal may not be the same. Therefore, the minimum illumination index can only be used for reference when designing and purchasing equipment.
4. Signal to noise ratio
The SNR is also a major parameter of the gun camera. When a gun camera captures bright scenes, the screen displayed by the monitor is usually brighter, and observers cannot easily see the noise in the screen. When the camera captures a dark scene, the screen displayed by the monitor is darker. At this time, it is easy to see snow-like noises in the picture. The strength of interference noise (that is, the degree of influence of interference noise on the picture) is directly related to the quality of the gun-type camera signal-to-noise ratio. That is, the higher the signal-to-noise ratio of the gun camera, the greater the influence of interference noise on the picture. small.
The so-called "signal-to-noise ratio" refers to the ratio of the signal voltage to the noise voltage, which is usually represented by the symbol S/N. Since in general the signal voltage is much higher than the noise voltage, the ratio is very large. Therefore, the actual calculation of the camera signal-to-noise ratio is usually based on the ratio of the mean square signal voltage to the mean square noise voltage. The number is multiplied by a factor of 20, that is, the unit of equation (2-3) is expressed in dB.
The signal-to-noise ratio given by the general gun camera is the value when the AGC (automatic gain control) is turned off, because when the AGC is turned on, the small signal is boosted, so that the noise level is also increased accordingly. The typical value of the CCD gun camera signal to noise ratio is generally 45dB ~ 55dB. When measuring SNR parameters, a video clutter measuring instrument should be used to connect directly to the video output terminal of the gun camera.
Gun Camera Features
The gun camera is powerful, widely used and cost-effective, and has the following features:
In recent years, with the extensive application of security surveillance cameras, high-definition gun camera imaging technology, high-definition fog function, infrared detection lock, day and night conversion infrared camera functions have been widely used in television monitoring projects. The day and night conversion infrared camera function of the gun-type camera enables the camera to perform filter switching between day and night, detect infrared light, and solve the frequent day and night conversion problems of ordinary day and night cameras. It can effectively reduce the noise of the image under nighttime low illumination conditions and improve the picture quality. The zoom range of the gun camera depends on the lens you choose, from several times to ten times, and the lens replacement is very convenient. According to the choice of different lenses, to achieve long-distance or wide-angle monitoring, there are many applications. In the use of road monitoring, even if the range of vehicle speed changes is relatively large, the bolt camera can also provide a clear picture. Through the built-in light suppression function, manual electronic shutter settings, to achieve the license plate capture. It can truly reproduce nighttime dynamic scenes and is suitable for places such as highways, toll stations, and safe cities that are monitored 24 hours a day.
Basic function analysis 1. The number of pixels
The number of pixels refers to the maximum number of pixels of the gun camera CCD sensor, and some of them give the number of pixels in the horizontal and vertical directions, such as 500H× 582V, and some give the waited product values ​​of the first two, such as 300,000 pixels. For a CCD chip of a certain size, the larger the number of pixels, the smaller the area of ​​each pixel unit, and the higher the resolution of a gun camera composed of the chip.
2. Resolution
Resolution is an important parameter to measure the advantages and disadvantages of black and white gun cameras. It means that when a gun camera takes equally spaced black and white stripes, it can be seen on a monitor (which should have a higher resolution than the camera). When the number of lines exceeds this number, only a grayed-out screen can be seen and black and white lines can no longer be distinguished.
The resolution test usually uses a gun camera to capture a resolution test card and read the data through a waveform monitor. The specific method is as follows:
(1) Arrange the test environment. Place the resolution test card on the standard test light box, about 3m away from the camera. The video output of the gun camera is connected to a waveform monitor and the output of the waveform monitor is connected to a high resolution black and white monitor.
(2) The illuminance of scenery is set to 2000lx, and the color temperature of the light source is set to 3200K.
(3) Adjust the lens focal length (or select the appropriate fixed-focus lens and move the camera forward or backward slightly) to fill the monitor screen with the image of the resolution card and sharpen the image with precise focusing.
(4) Observe the resolution card with the selected oscilloscope to get the waveform.
(5) Adjust the lens aperture so that the signal white level reaches 100% (70mV). At this time, the number of TV lines whose modulation is deeper than 5% is the limit resolution.
3. Minimum illumination
The minimum illumination is also an important parameter to measure the merits of the gun camera. Sometimes the word “lowest†is omitted and it is simply referred to as “illuminanceâ€. The minimum illuminance is a luminosity value of the scene when the illuminance of the subject is low to a certain extent and the level of the video signal output by the gun camera is as low as a predetermined value. When measuring this parameter, the maximum relative aperture of the lens should also be specified. For example, with an F1.2 lens, when the brightness of the subject is as low as 0.04LX, the amplitude of the video signal output by the camera is 50% of the maximum amplitude, ie, 350mV (the maximum amplitude of the standard video signal is 700mV. ), the minimum illumination of this gun camera is called 0.04LUX/F1.2. The brightness value of the subject was low, and the amplitude of the video signal output by the gun camera was less than 350mV. Reflected on the screen of the monitor, it would be a gray image with a hardly distinguishable level.
At present, due to the fact that the market's specifications are not yet uniform, the low illumination characteristics of some gun cameras with low illumination indices may not be as good as the low illumination characteristics of gun cameras with slightly higher illumination indexes. The reason for this is that the standards used in the measurement of low-lightness indicators are different. Still taking the above example as an example, if the amplitude of the video signal output by the camera is reduced to 30% of the maximum amplitude (that is, 210mV) as a reference, the brightness value of the imaged object can be further lowered, such as 0.03LX, If the optical lens is further replaced by an F1.0 lens, the brightness of the subject can be further reduced due to the increase of the luminous flux, such as 0.02LX.
It can be seen from the above analysis that it is impossible to accurately determine which camera has low illuminance characteristics by putting aside the measurement standard and simply comparing the illuminance nominal value of a certain brand of gun camera with the illuminance nominal value of another brand of gun camera. Good conclusions, because the relative aperture of the lens they use and the specified value of the output video signal may not be the same. Therefore, the minimum illumination index can only be used for reference when designing and purchasing equipment.
4. Signal to noise ratio
The SNR is also a major parameter of the gun camera. When a gun camera captures bright scenes, the screen displayed by the monitor is usually brighter, and observers cannot easily see the noise in the screen. When the camera captures a dark scene, the screen displayed by the monitor is darker. At this time, it is easy to see snow-like noises in the picture. The strength of interference noise (that is, the degree of influence of interference noise on the picture) is directly related to the quality of the gun-type camera signal-to-noise ratio. That is, the higher the signal-to-noise ratio of the gun camera, the greater the influence of interference noise on the picture. small.
The so-called "signal-to-noise ratio" refers to the ratio of the signal voltage to the noise voltage, which is usually represented by the symbol S/N. Since in general the signal voltage is much higher than the noise voltage, the ratio is very large. Therefore, the actual calculation of the camera signal-to-noise ratio is usually based on the ratio of the mean square signal voltage to the mean square noise voltage. The number is multiplied by a factor of 20, that is, the unit of equation (2-3) is expressed in dB.
The signal-to-noise ratio given by the general gun camera is the value when the AGC (automatic gain control) is turned off, because when the AGC is turned on, the small signal is boosted, so that the noise level is also increased accordingly. The typical value of the CCD gun camera signal to noise ratio is generally 45dB ~ 55dB. When measuring SNR parameters, a video clutter measuring instrument should be used to connect directly to the video output terminal of the gun camera.
Gun Camera Features
The gun camera is powerful, widely used and cost-effective, and has the following features:
In recent years, with the extensive application of security surveillance cameras, high-definition gun camera imaging technology, high-definition fog function, infrared detection lock, day and night conversion infrared camera functions have been widely used in television monitoring projects. The day and night conversion infrared camera function of the gun-type camera enables the camera to perform filter switching between day and night, detect infrared light, and solve the frequent day and night conversion problems of ordinary day and night cameras. It can effectively reduce the noise of the image under nighttime low illumination conditions and improve the picture quality. The zoom range of the gun camera depends on the lens you choose, from several times to ten times, and the lens replacement is very convenient. According to the choice of different lenses, to achieve long-distance or wide-angle monitoring, there are many applications. In the use of road monitoring, even if the range of vehicle speed changes is relatively large, the bolt camera can also provide a clear picture. Through the built-in light suppression function, manual electronic shutter settings, to achieve the license plate capture. It can truly reproduce nighttime dynamic scenes and is suitable for places such as highways, toll stations, and safe cities that are monitored 24 hours a day.
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