Number Plate Recognition (ANPR)

Subject to license

ANPR, Number Plate Recognition, is an image analysis method, requiring a license, for recognition of number plates on moving and stationary vehicles at a maximum distance of 20 m and a speed of up to 100 km/h.

The plates that are recognized are put into a Black/White list under optional categories and an action is sent that can be utilized with the event/alarm configuration.

Using the identification of the vehicle plate, it is possible to, for instance, control entrance gates etc. in parking lots, loading areas, entrances to a property, etc.

Recognition Rates

The typical recognition rate is > 96 %. Decisive factors for the maximum recognition rate are:

Decisive factors	Description
the country plates involved	The vehicle plates of various countries can differ in the font type, size, syntax used and the quality of the lettering. Additionally, the reflection behavior differs, as do the character order, character contrast and character color and, of course, the background color.
the ambient light	Insufficient lighting makes recognition more difficult, as the character color and background color “blur” and several fonts have too little contrast due to their size.
the perspective of the recording	Depending on the vertical and horizontal orientation of the camera, dis-tortions occur. There can also be problems due to the shearing of the characters.

Optimizing the system parameters can make it possible, even for problematic plates, to achieve high recognition rates, which can come very close to the > 96 % mentioned above.

Practical experience has demonstrated that the recognition quality is not only dependent on the parameter settings, but also on external factors. This includes the resolution of the camera and the thus available "size” of the characters to be recognized.

Additionally, the quality of the images depends on the environment and the external conditions during recording. These days, the resolution of the images can be positively influenced, easily and inexpensively, with an appropriate selection of a digital camera. Unfavorable light and ambient conditions can be controlled with lighting or the selection of an appropriate camera location. A portion of possible disturbances can be compensated with software by brightening, increasing the contrast, rotation, etc.