PPF (Pixel Per Foot)

What is PPF

PPF (Pixels Per Foot), is a level of pixel density, where pixel stands for "picture element" and is the smallest unit of a digital image or display. Pixels are individual dots of color that together make up the image seen on screens such as computers, smartphones, and televisions.

Sometimes pixel density is confused with resolution. Resolution describes the total number of pixels in an image, or the total number of pixels in an image sensor, usually described in terms of width x height, and it doesn't relate to how many of those pixels are focused on a specific object or area of the image, which means that the same resolution picture will have different clarity on different sizes of displays. Whereas PPF provides a standardized way to assess the sharpness and detail of an image, especially in applications that require precise image analysis.

PPF Calculation Formula:

PPF = Number of Pixels / Display Area (in feet)

Example:

If a digital display has a resolution of 1920x1080 pixels and the display area is 4 feet wide, the PPF can be calculated as follows.  Total pixels in one foot width = 1920 pixels / 4 feet = 480 PPF

PPF in Video Surveillance

In the field of security surveillance, the concept of Pixels Per Foot (PPF) is frequently used because it plays a crucial role in image clarity, detail representation, and overall monitoring effectiveness. A higher PPF means more pixels per foot are covering the area, providing clearer and more detailed images, which allows the surveillance system to more effectively identify and analyze objects and events within the scene. The main factors affecting the PPF in video surveillance are as follows:

• 1. Resolution: The higher the resolution of the camera, the higher the PPF, because a high-resolution camera can provide more pixels.

• 2. Field of view: The range of viewing angles has a significant impact on PPF. Wide viewing angles cover a larger area but have a lower PPF because the pixels are distributed over a larger area, whereas narrow viewing angles focus on covering a smaller area and have a higher PPF, which improves image detail and clarity.

• 3. Installation position: The installation position of the camera also affects the PPF, the higher it is installed, the larger the ground area it covers, and the lower the PPF may be; whereas, a proper installation angle can optimize the camera's viewing angle range, improve the PPF, and ensure that key areas are monitored.

By the way, high PPF levels should not be pursued in security monitoring, because the larger the PPF, the more storage space required, which will lead to increased costs or shorter video storage time. We should combine the application scenario with the actual needs to choose the most suitable PPF.

Choosing the Right PPF for Camera Deployment

When we deploy cameras, how to choose the right PPF according to the deployment location, environment, and specific functional requirements? Combined with industry practice and relevant specifications, we give three common application scenarios and the corresponding PPF range as a reference for your selection:

• Large Scope Monitoring: 30-40 PPF

This PPF range can recognize the main activities and events, and has a certain degree of clarity. It is suitable for large area surveillance, such as parking lots, plazas, warehouses, etc., providing basic activity monitoring and area coverage.

• Face Recognition: 50-60 PPF

Cameras in this PPF range can accurately recognize and verify faces and are suitable for scenes such as bank entrances, office building entrances, and security check lanes. It can provide high-resolution images that can clearly capture and recognize facial features.

• License Plate Recognition: 60-100 PPF

This range of PPF can provide enough detail to accurately read license plate numbers under different lighting conditions, even when the vehicle is in motion. It is suitable for parking lot entrances, road surveillance, toll booths, and other scenarios where license plate information needs to be read.

In addition, various advanced analysis functions (face search, human detection, etc.) often have specific PPF requirements, and if the PPF of the images does not reach the required value, the analysis will not include these images in the retrieval range. In order to increase the detection and analysis distance of the camera, we can use optical zoom to obtain long-range clarity, but zoom causes the picture to be cropped, sacrificing the field of view while increasing the PPF.

FAQs

Q1: Why is PPF important for video surveillance?

Pixels Per Foot (PPF) is a key metric in video surveillance that plays a vital role in ensuring image quality and detail capture. When planning a camera deployment, PPF provides a metric to help select the right camera and mounting location to ensure that the desired level of detail is achieved throughout the surveillance area.

Q2: Why is PPF important for video surveillance?

A high PPF ensures that the camera is able to capture clear facial features, which is essential for recognizing and verifying faces. According to practical experience, 50 PPF is the minimum requirement for face recognition.

Q3: How does optical zoom impact PPF?

Optical zoom increases the PPF by focusing on a smaller area, which enhances the detail of the monitored scene. However, it also reduces the overall field of view, which might limit coverage.

Q4: Can PPF be adjusted?

Yes, PPF can be adjusted by changing the camera resolution, adjusting the camera's field of view, or modifying the camera placement to alter the monitored area's size.

Q5: Can software enhance PPF?

The software can enhance image clarity through digital zoom and post-processing, but it cannot increase the actual PPF captured by the camera. Physical adjustments and higher resolution cameras are needed to truly increase PPF.