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How to choose a security camera from pixel density?

The pixel density of the camera refers to the number of pixels in a certain range, which is an important indicator to measure the clarity of the image taken by the camera.

 

FCB-EV9520L

 

1. Definition and calculation method

Definition: Pixel density refers to the number of pixels per unit area on the camera image sensor, or refers to the number of pixels in a certain field of view (such as horizontal direction). It reflects the camera’s ability to capture detail.

Calculation method: The calculation formula of pixel density is: pixel density = camera horizontal resolution ÷ field of view (left to right). For example, if the camera has a horizontal resolution of 1920 pixels and a field of view of 1920 centimeters (that is, about 2 meters), the camera has a pixel density of 1 pixel/centimeter, or 100 pixels/meter (that is, 100PPM).

 

2. Influencing factors

Camera resolution: The higher the resolution of a camera, the higher its pixel density is usually. High-resolution cameras are able to capture more detail, providing sharper images.

Lens focal length: The focal length of the lens also affects the pixel density. At the same camera resolution, using a telephoto lens can reduce the field of view and thus increase the pixel density. In contrast, using a wide-angle lens will increase the field of view and reduce the pixel density.

Monitoring distance: As the monitoring distance increases, the pixel density decreases. In order to maintain the same pixel density at different monitoring distances, it is necessary to change the telephoto lens or increase the resolution of the camera.

 

How to choose a security camera from pixel density? - Sony Camera Information - 2

 

3. Select according to the monitoring purpose

A. Pixel density standard
Select the pixel density according to different monitoring purposes, and the required pixel density is different for different monitoring purposes. Generally divided into verification (Identification), Recognition (Recognition), Observation (Observation), Detection (Detection) and Monitoring (Monitoring) different levels.

 

1. Identification
Criteria: Verification usually involves confirmation of the identity of a particular individual or object. In surveillance systems, this usually means confirming identity by comparing known information (such as faces, license plate numbers, etc.) with information in the surveillance screen. The criterion for verification is accuracy, that is, the ability to correctly identify the target individual or object and exclude false positives and false positives.
Application: Authentication is particularly important in scenarios that require high security authentication, such as access control systems and financial transaction verification.

 

2. Recognition
Criteria: Identification refers to the classification or naming of individuals or objects in the surveillance screen. In contrast to verification, identification does not require confirmation of identity, but rather the ability to distinguish between different individuals or objects. The criteria for recognition are the accuracy and robustness of the classification, that is, the ability to correctly identify the target under different environments, lighting and angles.
Application: Recognition is widely used in intelligent monitoring systems, such as face recognition, license plate recognition, behavior recognition, etc.

 

3. Observation
Standard: Observation refers to the real-time and continuous monitoring of the monitoring screen, and the recording of relevant data and information. The standard of observation is real-time and integrity, that is, the ability to capture changes in the monitoring screen in real time, and record all important information.
Application: Observation applies to scenarios that require real-time monitoring and recording, such as public security monitoring and traffic monitoring.

 

4. Detection
Standard: Detection refers to the detection of abnormal behavior in the monitoring screen. This usually involves the judgment of preset rules or thresholds, and when the behavior or state in the monitoring screen meets these rules or thresholds, the system triggers an alarm or takes other action. The criteria for detection are sensitivity and accuracy, that is, the ability to detect abnormal behavior in a timely manner and reduce false positives and missed positives.
Application: Detection is particularly important in scenarios that require rapid response to abnormal behaviors, such as intrusion detection and fire detection.

 

5. Monitoring
Standard: Monitoring is the continuous observation and recording of all activities within the scope of monitoring. In contrast to observation, surveillance focuses more on monitoring the environment as a whole, rather than focusing on specific individuals or objects. The standard for monitoring is comprehensiveness and continuity, that is, the ability to cover all areas within the monitoring range and continuously record relevant information.
Application: Monitoring is suitable for scenarios that require a comprehensive understanding of activities within the monitoring scope, such as factory production line monitoring, warehouse security monitoring, and so on.

 

How to choose a security camera from pixel density? - Sony Camera Information - 3

 

B. Johnson Principle

The Johnson criterion, developed by American physicist John Johnson in the 1950s, is a method for predicting the performance of sensor systems, particularly in the field of infrared thermal imaging to determine the minimum resolution required to detect objects. Based on experiments, the problem of target detection is associated with equivalent fringe detection, and the target recognition ability of infrared imaging system is determined by the resolution of equivalent fringe.

 

The Johnson criterion divides target detection into three levels:
1. Detection: A target is found in the field of view. At this time, the image formed by the target must occupy more than 1.5 pixels in the direction of critical size.
2. Recognition: The target can be classified, and the target can be identified as a tank, truck or person. At this time, the image of the target must occupy more than 6 pixels in the direction of critical size.
3. Identification: It can distinguish the model and other characteristics of the target, such as identifying the enemy and ourselves. This means that the image of the target must occupy more than 12 pixels in the direction of critical size.

 

C. Eu EN62676-4:2015, EN50132-7:2012

1. En 62676-4:2015:
This standard is called “Video surveillance systems for use in security applications – Part 4: Application guidelines, “Video Surveillance Systems for Security Applications – Part 4: Application Guidelines.”
It provides recommendations and requirements for the selection, planning, installation, commissioning, maintenance and testing of video surveillance systems (VSS) for security applications.
The standard is designed to help customers, installers and users establish their own requirements, help descriptors and users determine the appropriate equipment required for a given application, and provide a method for objectively evaluating the performance of video surveillance systems.

2. EN50132-7:2012:
This standard is called “Alarm systems – CCTV surveillance systems for use in security applications – Part 7: Application guidelines, “CCTV surveillance systems for Alarm systems for security applications – Part 7: Application Guidelines”.

 

Sum up

In summary, the camera selection can be conducted more scientifically from the perspective of pixel density to ensure that the monitoring system can meet specific monitoring needs.

In practical applications, these grades may overlap and cross each other. For example, an intelligent monitoring system may have the ability to verify, identify, and detect simultaneously. In addition, with the continuous development of technology, the standards of these grades are constantly improving and improving. Therefore, when selecting a surveillance camera system, it is necessary to determine the required level and standard according to the specific application scenarios and needs.

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