The importance of the configuration and screen debugging of security surveillance cameras is self-evident. If the camera picture is not properly configured and debugged according to the specific structure, environmental conditions and target object of the building, even if the resolution of the camera is higher, the technical level of the system reaches the highest standard, but the image of the camera appears in a top view and a side view. The backlighting, the effective picture is small, and even when there are problems such as blind spots and dead ends, the monitoring image still fails to achieve the expected effect and effect.
Then, in the engineering practice, what are the problems that directly affect the image quality and the effectiveness of the camera configuration and screen debugging, and what measures are taken to improve and improve the image quality?
The configuration of the camera should be reasonably standardized
The configuration of security cameras should be reasonable, standardized and unified to meet the requirements of technical standards. If you have thoroughly and carefully analyzed the requirements for the use of surveillance images in the technical defense standards, you will find that the security surveillance images can be divided into three levels according to the level of detail displayed and the characteristics of the objects reflected. One is to display the facial features of the person or the motor vehicle number, the second is to display the physical characteristics of the person and the activities of the personnel, and the third is to display the activities of the personnel or vehicles in a particular area or site and the behavioral characteristics of the personnel and the vehicle. . It can also be seen that not all the monitoring images of the place can clearly display the facial features of the person, and the monitoring range of the camera mainly depends on the characteristics of the object to be reflected.
The contents of the above table indicate that the first level or the most demanding is the image of the entrance and exit of the courtyard and the entrance and exit of the building. It is required to clearly display the facial features of the entering and exiting personnel and the motor vehicle number. For this reason, the view of each camera The field angle is the smallest, the monitoring range is within a few meters (not more than 10 meters); the second level is the image of the corridors and passages of the building, which is required to display the physical characteristics and activities of the person. For this purpose, each camera The angle of view is moderate, the monitoring range is generally more than 10 meters (not more than 20 meters); the third level or relatively low requirements are for parking lot passages, road main roads, parking lots, squares, halls, perimeters, etc. The image is only required to display the activity and behavior characteristics of the person and the vehicle. For this reason, the angle of view of each camera is the largest, and the monitoring range is generally from 10 meters to more than 100 meters (not more than 200 meters). In the area, each camera monitors a range of 10 square meters to more than 100 square meters.
Monitoring images of entrances and exits should not have blind spots or dead ends
In order to ensure that the surveillance image of the entrance and exit should not have blind spots or dead angles, the configuration of the entrance and exit cameras should adopt different schemes depending on different situations. First, we should understand the relevant situation. First, we must see if there is any problem of backlighting at the entrance and exit of the camera. Second, we must Look at the internal structure of the entrance and exit of the installation camera is a straight channel or an entrance (such as a hall or lobby) with a certain wall width on both sides. Then take different scenarios according to the different situations above. If there is no backlight problem at the entrance and exit, the entrance and exit camera should be installed in the direction of the entrance and exit, so that the camera can monitor the personnel entering the entrance and exit, and in order to ensure that the monitoring image does not have the blind zone problem, the border of the entrance and exit can be displayed on the display. Figure 1.
If there is a problem of backlighting at the entrance and exit, in order to avoid the backlighting of the image, the camera should be installed with the entrance and exit direction, so that the camera can monitor the personnel leaving the entrance and exit. At this time, it is necessary to pay attention to distinguishing the internal structure of the entrance and exit, if the entrance and exit The internal structure is a straight channel with a width of 3m to 4m. If a person has to go through this channel before leaving the entrance and exit, a camera can be installed to monitor the straight passage inside the entrance; if the inside of the entrance and exit is an area with a certain width In the case of a lobby or hall, in order to avoid installing a camera, someone will leave the entrance and exit on both sides of the entrance and exit, causing blind spots or dead spots in the surveillance image. At this time, two or more cameras should be installed. By means of two or more cameras complementary to the blind spots or dead angles of the cameras, the image is completely covered to show the person leaving the entrance and exit. See Figures 2 and 3.
Increase the effective picture and depth of field
Each image highlights the subject of the target to be monitored, ie the effective picture. It is also necessary to further clarify that the theme or effective picture of the security surveillance image does not necessarily have to display the facial features of the person. As mentioned above, some have to display the facial features of the person, and some have to display the physical features of the person. And some only show the activity of the person or the vehicle, that is, the behavioral characteristics. Once the theme is clear, the picture should highlight the picture related to the theme, and the unrelated picture should appear as little as possible or even not.
We often encounter the problem that the effective image of the monitoring image is too small. For example, if the image of the entrance is monitored, it is often because the display screen of the wall on both sides of the entrance and exit is too large or too large, but the entrance and exit screen that needs to be focused on is seen. It is not big, that is, the display image does not highlight the theme of the entrance and exit, so that the screen of the entrance and exit personnel is too small, and the facial features of the person are not clear; if the image of the corridor passage is monitored, it is also because of the wall and ceiling on both sides of the passage. Too much or too much, the picture of the promenade or the passageway is not too much or too small, so that the physical characteristics and activities of the walking people in the corridor or passage are not clear.
In this regard, there is a situation in which the effective image of the pseudo-image is not enough, and we can overcome it by adjusting the focal length of the camera, so as to achieve the picture requirement sufficient to distinguish the target feature. However, while solving one problem, it may cause another problem. Because of an ideal image, in addition to the above effective image that can be used to identify the target features, there must be a certain depth of field. Anyone who has participated in the screen debugging knows that the effective picture and depth of field of the image are a contradiction. The effective picture will directly affect the depth of the picture. In addition, if the effective picture is too large, the moving target will move too fast. The time of the person or vehicle appearing in the image is very short and flashes past. Eventually, when the need for forensics is required, the screen for intercepting the target feature will not be clear. Therefore, the effective picture is not as big as possible.
We must correctly handle the relationship between the effective image and the depth of field of the image. In the screen debugging of the security surveillance image, the effective image of the image only needs to be able to see the characteristics of the monitoring target. It is enough to correctly identify the characteristics of others or vehicles. It does not need to be too large. If it is too large, it will directly affect the depth of field of the picture, affecting the observation of the characteristics of the movement process of the person or the vehicle. The observation of the characteristics of the movement process of the person or the vehicle is also part of the security monitoring content. The advantages and disadvantages of the effective picture and depth of field of the image are shown in Figures 4 and 5.
Avoid image appearance and side view
Technical standards for technical defenses are stipulated. The installation height of security cameras should not be less than 2.5m indoors and less than 3.5m indoors. This is mainly to avoid the normal walking of vehicles or the normal operation of vehicles after the camera is installed too low. Driving. However, in the actual installation, if only the above problems are avoided, the installation height control requirements of the camera are within the range, and the image viewing angle problem may occur, and the image may have a top view or a side view problem, and the image may have a top view or a side view problem. The monitoring image does not function to identify the target feature.
The image does not appear to have a side or side view problem. The key is to see the angle between the camera's pointing and the monitoring target (ie, the angle of view). This angle is divided into the vertical angle and the horizontal angle (the vertical angle is the camera's pointing and monitoring target). The formed high and low angles and horizontal angles are the horizontal angles formed by the pointing of the camera and the front direction of the monitoring target). Actually, when the vertical angle formed by the pointing of the camera and the monitoring target is ≤30°, the image does not appear to have a top view. When the angle between the pointing of the camera and the front direction of the monitoring target is ≤45°, the image does not appear side-viewing. After the installation angle of the camera reaches the above requirements, the image display can basically reflect the positive features of the monitored target. Of course, the smaller these angles are, the more beneficial it is to improve the image of the image, see Figure 6 and 7.
In view of the above two problems and requirements, that is, without affecting the normal walking of the person or the vehicle, the installation height of the camera should not be too low, and the image should not be tilted or side, the camera pointing and the monitoring target The angle should not be too large. For this, the best or most appropriate solution is to set the camera away from the surveillance target a little further, not too close. Practical experience shows that the distance between the two indoors should not be less than 3.5m, and the distance between the two should not be less than 4m. However, the distance between the two should not be too large. Although the distance is large, it is beneficial to improve the image of the image. However, because the distance between the two is large, the monitored object will be affected by other foreign objects in the middle of the two. The probability of occlusion increases.
The installation orientation of the entrance and exit cameras is consistent
Everyone should know that when there are multiple entrances and exits in the same part of the building, if the cameras installed on the respective entrances and exits are inconsistent, it may be possible for the unscrupulous people to take advantage of them, and the images monitored by the cameras are all human. The back image does not show the frontal image of the person (though it is even more difficult to distinguish the facial features of the person). This problem is also caused when the technical defense engineering practitioners often do not pay attention to the construction of the project. According to the location of the entrance and exit of the building, it can be divided into three types of entrances and exits, one is the perimeter or the entrance and exit of the courtyard, the other is the entrance and exit of the building to the outside, and the third is the entrance and exit of the indoor floor, that is, the elevator hall and the stairway.
For the camera installation orientation of the perimeter or courtyard entrance and exit, it is generally better to monitor the orientation of the person or vehicle entering the entrance and exit. This is because, on the one hand, the image that enters the entrance and exit is better than the image that leaves the entrance and exit, and the other is better. In terms of the fact that the camera is installed in the area under its jurisdiction, it is more feasible than outside the jurisdiction (the camera is generally not allowed to be installed outside the jurisdiction). For the camera installation orientation of the entrance and exit of the building to the outside, generally in order to avoid backlighting, it is better to face the entrance and exit to monitor the installation orientation of the person leaving the port. For the camera installation orientation of the indoor floor entrance and exit, only the requirements are the same, and the orientation is not emphasized. Here, it should be pointed out that the installation orientation of the indoor floor entrance and exit cameras is the same, which means the installation of all the entrance and exit cameras on each floor. The orientation is the same, and it does not mean that the camera mounting orientations of all the entrances and exits between the layers are also the same, and the installation orientation of the entrance and exit cameras between the layers may be inconsistent. With the three-port entrance and exit camera installed in the same direction, it can ensure that any person entering or leaving the perimeter or the courtyard can at least take in three front images. If it is only in and out of the building, at least Take in two frontal images.
In summary, there are many factors that affect the image quality effectiveness, in addition to the well-known camera clarity and other technical parameters, as well as the number, position, angle, light and screen debugging of the camera installation and configuration. Direct relationship, which one of the links has a problem, monitoring images will affect the actual effect.
In the construction of security engineering, engineering and technical personnel should pay full attention to the configuration of the camera and the debugging of the screen while selecting the camera with good technical performance. In the design and construction, only by combining the specific building structure, environmental conditions and target objects of the building, through repeated and careful comparison, exploration and summary, the configuration and debugging of each camera can be justified, thus achieving the best security. Monitor image effects.
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