3. Choice of resolution 4. Imaging sensitivity 8. The size of the CCD chip
CCD is the abbreviation of Charge Coupled Device, it is a semiconductor imaging device, so it has the advantages of high sensitivity, anti-glare, small distortion, small size, long life, anti-vibration and so on.
2. The working mode of CCD camera
The image of the subject is focused on the CCD chip through the lens. The CCD accumulates a corresponding proportion of charge according to the intensity of the light. The charge accumulated in each pixel is shifted out point by point under the control of the video timing. Video signal output. Connect the video signal to the video input terminal of the monitor or TV to see the same video image as the original image.
The index for evaluating the resolution of the camera is the horizontal resolution, whose unit is line pairs, that is, the number of black and white line pairs that can be resolved after imaging. The resolution of commonly used black and white cameras is generally 380-600, and the color is 380-480. The larger the value, the clearer the imaging. For general surveillance occasions, a black-and-white camera with about 400 lines can meet the requirements, such as our VS-870HC HD DSP zoom industrial camera; a 600-line camera can get a clearer image. Such as our company's VS-902H miniature high-definition camera, VS-250DM high-definition medical imaging camera, such products fully meet the special occasions of medical treatment, image processing and so on.
Usually the minimum environmental illumination requirement is used to indicate the camera sensitivity. The sensitivity of the black and white camera is about 0.02-0.5 Lux (lux), and the color camera is mostly above 1 Lux. The 0.1Lux camera is used for ordinary surveillance occasions; at night or when the ambient light is weak, it is recommended to use a 0.02Lux camera. When used with a near-infrared light, a low-illumination camera must also be used.
In addition, the sensitivity of the camera is also related to the lens, 0.97Lux / F0.75 is equivalent to 2.5Lux / F1.2 is equivalent to 3.4Lux / F1. Reference ambient illumination: 100000Lux under the summer sun and cloudy outdoor 10000Lux TV studio 1000Lux from 60W table lamp 60cm desktop 300Lux indoor fluorescent lamp 100Lux dusk indoor 10Lux 20cm candlelight 10-15Lux night street lamp 0.1Lux
5. Electronic shutter
The time of the electronic shutter is between 1 / 50-1 / 100000 seconds. The electronic shutter of the camera is generally set to the automatic electronic shutter mode. The shutter time can be automatically adjusted according to the brightness of the environment to obtain a clear image. Some cameras allow users to manually adjust the shutter time, such as MV-VE series GigE industrial network digital cameras to adapt to some special applications.
6. External synchronization and external trigger
External synchronization refers to the use of the same synchronization signal between different video devices to ensure the synchronization of video signals. It can ensure that the video signals output by different devices have the same frame and line start and end time. In order to achieve external synchronization, a composite sync signal (C-sync) or composite video signal needs to be input to the camera. External synchronization does not guarantee that users get a complete continuous frame of images from a specified time. To achieve this function, you must use some special cameras with external trigger functions.
7. Spectral response characteristics
The CCD device is made of silicon material, which is more sensitive to near infrared, and the spectral response can be extended to about 1.0um. The peak of its response is green light (550nm), and the distribution curve is shown on the right. In the case of covert surveillance at night, you can use near-infrared lamps to illuminate, so that the human eye cannot see the environment clearly, but it can clearly image on the monitor. Because the CCD sensor has a layer of transparent electrodes that absorb ultraviolet light, the CCD is not sensitive to ultraviolet light. The imaging unit of the color camera has red, green and blue filter bars, so the color camera is not sensitive to infrared and ultraviolet.
The imaging size of the CCD is commonly used 1/2 ", 1/3", etc., the smaller the imaging size, the smaller the camera volume can be made. Under the same optical lens, the larger the imaging size, the larger the angle of view. Chip Specifications Imaging Surface Size (Width X Height) Diagonal 1/2 6.4x4.8mm 8mm 1/3 4.8x3.6mm 6mm Camera Lens Selection Guide How to select the correct camera lens according to the monitored environment in the TV monitoring system It is very important, because it directly affects whether the effect of the monitored face painting seen on the monitor at the end of the system after the system is composed can meet the design requirements of the system (in terms of screen range or image details), so the correct Choosing the camera lens can optimize the system design and obtain a good monitoring effect.
Camera lens can be divided into manual aperture lens and automatic aperture lens in terms of aperture, and can be divided into fixed focus lens and zoom lens in terms of focal length.
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