License Plate Capture Shootoutby Antony Look, posted on May 22, 2011
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:
Inside the Pro section, we provide analysis on 14 scenes, revealing the performance of each camera in each scene. The 14 scenarios we choose were:
- Daytime LPC (Far)
- Daytime LPC (Mid)
- Daytime LPC (Near)
- Day vs Night LPC
- Ground Level vs High Mounting LPC
- 11ft vs 7ft Mounting LPC
- Low Beams vs High Beams LPC
- Headlamps Off vs Low Beams LPC
- Nighttime Van LPC (Ambient Lighting)
- Nighttime Van LPC (White Light LED)
- Nighttime Van LPC (IR LED)
- Nighttime Sedan LPC (Ambient Lighting)
- Nighttime Sedan LPC (White Light LED)
- Nighttime Sedan LPC (IR LED)
Many factors impact performance, making LPC one of the most challenging achievements in surveillance, especially when the camera is being used for both license plate capture and general surveillance. Inside, we show and explain each of the key factors involved.
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