The backlight phenomenon at entrances and exits is a more prominent problem in the installation and use of video surveillance. To solve this problem, we have not found a completely effective method. The three methods introduced below have a certain effect on improving the backlight phenomenon. We are using In the process, it is necessary to comprehensively consider the on-site environment and many other conditions, so as to find the best solution.
Generally speaking, there are three main ways to solve the backlight of the camera. One is to avoid direct sunlight when installing the camera; the other is to use a camera with corresponding improvement functions, such as a wide dynamic camera or a backlight compensation camera; the third is to increase the illumination of the indoor light source. Reduce the contrast with outdoor light.
First, adjust the installation position of the entrance and exit camera to avoid direct sunlight from the outside as much as possible, which can greatly improve the backlight phenomenon of the entrance and exit. For example, a camera needs to be installed at the entrance of a bank to monitor people entering and exiting. If we install the camera toward the entrance and exit, we may encounter a serious backlight phenomenon, which will cause the surveillance picture to be blackened and the real object can not be seen clearly. At this time, an experienced engineer will flip the camera that monitors the entrance and exit so that the camera lens faces the personnel who walk out of the outlet. This is better than installing the camera toward the entrance and exit, and can better solve the backlight problem.
Second, by selecting cameras with corresponding functions, the backlight phenomenon can be improved. There are two types of cameras in security cameras that can better solve the problem of camera backlighting. One is a camera with a backlight compensation function, and the other is a wide dynamic camera.
Backlight compensation, also known as backlight compensation, divides the picture into several different areas, and each area is exposed separately. In some applications, the field of view may contain a very bright area, and the contained subject is surrounded by a bright field, and the picture is dim and without layers. At this time, because the signal level detected by the AGC is not low, the gain of the amplifier is very low, which cannot improve the brightness of the main body of the picture. When the backlight compensation is introduced, the camera only detects a sub-area of the entire field of view. The average signal level in this area determines the operating point of the AGC circuit. Because the average level of the sub-area is very low, the AGC amplifier will have a higher gain, which will increase the amplitude of the output signal, so that the main picture on the monitor is clear, and the subjective brightness difference between the background picture and the main picture is greatly reduced. The visibility of the field of view is improved. Although the backlight compensation improves the brightness of the subject, the image quality is more or less degraded.
Wide dynamic is to expose twice at the same time, once fast and once slow, and then synthesize to make it possible to see bright and dark objects on the screen at the same time. Both are measures taken to overcome the goal of seeing clearly under strong backlight conditions, but the backlight compensation is at the expense of the contrast of the picture. In a sense, the wide dynamic technology is an upgrade of the backlight compensation.
Third, improve the backlight phenomenon by increasing the illuminance of the indoor light source. It is conceivable that the cause of the backlight phenomenon is caused by the high contrast of the light intensity in the field of view. The camera installed at the entrance and exit has strong outdoor light in the monitoring range and weak indoor light, which forms a black and white image contrast. Too strong. In this way, if the illuminance of the indoor light source is increased, the indoor light is enhanced, and the contrast between the indoor and the outside light is reduced, and the backlight phenomenon can also be improved.
