[ Huaqiang Security Network News ] The image quality of the camera is an important part for the customer who installs the monitoring system. If the image quality of the camera is not good, it will affect the monitoring effect. Let's analyze the four main points of camera image quality. 
1. Vertical resolution <br> The vertical resolution is determined by the number of scan lines in the TV system. The PAL system indicates that the effective scanning line of one frame is 625 lines, and the average field has 20 lines of vertical blanking time. Therefore, only 585 lines appear in the actual picture. In addition, since CCTV uses a progressive scan method, the resolution is lowered. The ratio is called the Kyle coefficient, and empirically, a value of 0.7 is used. Thus, the final vertical resolution HV = (625-20x2) x 0.7, about 410 lines is the limit of vertical resolution. As mentioned above, the vertical resolution is determined by the TV system and does not represent the performance of the camera.
2, horizontal resolution <br> This is one of the important indicators of CCTV surveillance camera performance. The actual CCD used determines the clock frequency and sampling frequency. The sampling frequency of the high-resolution CCD is 14.18 MHz. According to the Shannon sampling principle (the sampling frequency must be more than twice the upper limit of the continuous signal), the image signal frequency is limited to about 7 MHz.
In addition, if the image signal component has a frequency component exceeding 1/2 of the sampling frequency, a folding phenomenon will occur, and a false signal/molar image will be produced. In order to prevent this, it is necessary to use a high-efficiency band-pass filter at a frequency of 7 MHz or more. It is actually difficult to manufacture such a filter, and therefore, the image signal frequency becomes about 6 MHz, and the horizontal resolution reaches 480 lines.
3. Sensitivity
Another important feature of CCTV surveillance cameras is the illumination (sensitivity) of the lowest subject. The so-called minimum subject illumination is the "required subject illumination required to obtain an image output level that can recognize the lowest bound of the subject", expressed in lux (lux).
4. Ambient illumination <br> It is recommended that the engineer perform a comprehensive test on the camera (including lens) to be installed, focusing on vertical and horizontal resolution test, color reproduction test, linearity test, focus test, face recognition level test, Impedance matching feature test, especially in the installation environment illumination test, when the installation environment illumination cannot be confirmed, refer to the office, public room, living room, star hotel lighting design reference value. As the engineering company has more video surveillance projects, it should purchase special equipment to fully test the camera (including the lens).
2, horizontal resolution <br> This is one of the important indicators of CCTV surveillance camera performance. The actual CCD used determines the clock frequency and sampling frequency. The sampling frequency of the high-resolution CCD is 14.18 MHz. According to the Shannon sampling principle (the sampling frequency must be more than twice the upper limit of the continuous signal), the image signal frequency is limited to about 7 MHz.
In addition, if the image signal component has a frequency component exceeding 1/2 of the sampling frequency, a folding phenomenon will occur, and a false signal/molar image will be produced. In order to prevent this, it is necessary to use a high-efficiency band-pass filter at a frequency of 7 MHz or more. It is actually difficult to manufacture such a filter, and therefore, the image signal frequency becomes about 6 MHz, and the horizontal resolution reaches 480 lines.
3. Sensitivity
Another important feature of CCTV surveillance cameras is the illumination (sensitivity) of the lowest subject. The so-called minimum subject illumination is the "required subject illumination required to obtain an image output level that can recognize the lowest bound of the subject", expressed in lux (lux).
4. Ambient illumination <br> It is recommended that the engineer perform a comprehensive test on the camera (including lens) to be installed, focusing on vertical and horizontal resolution test, color reproduction test, linearity test, focus test, face recognition level test, Impedance matching feature test, especially in the installation environment illumination test, when the installation environment illumination cannot be confirmed, refer to the office, public room, living room, star hotel lighting design reference value. As the engineering company has more video surveillance projects, it should purchase special equipment to fully test the camera (including the lens).
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