License Plate Capture

Capturing license plates is one of the best ways to identify suspects and intruders. As such, it is highly desirable that outdoor surveillance cameras are able to do so.

However, capturing license plates is challenging. While license plates are relatively small, surveillance cameras are generally expected to cover a large area. Even worse, at night time, headlights make capturing license plates quite hard.

In the last few years, hopes have risen as megapixel cameras have become mainstream. Theoretically, the much greater resolution should allow for simultaneous wider coverage areas and capturing of license plates.

In this report, we share our results from a real world license plate capture (LPC) test. We choose a two lane vehicle entrance to a public parking facility with a kit of 5 IP cameras (including SD, 720p, 3MP and 5MP cameras from Axis, Arecont Vision, Bosch, Sony and StarDot) to better understand the tradeoffs ourselves. As the image below shows, we captured a moderately wide Field of View focused on the two lane entrance:

We placed our camera kit in line with the vehicle entrance to capture vehicles entering and exiting the lot. The overhead image and map below demonstrates the coverage, distances and pixels per foot at different positions.

Then we analyzed a series of scenes to see how performance varied across the cameras. We digitally zoomed each camera to the same level to see the differences. Below is an example of our analysis: