Milestone Analytics 2.2 Dacolian LPR - Manual (Page 40)

Milestone XProtect Analytics 2.2 – Dacolian LPR; Administrator’s Manual
www.milestonesys.com Page 40 Camera Tips & Tricks
gain noise and motion blur in the images, and ultimately to underexposure.
Underexposure can be avoided by using sufficient external lighting and/or by using
a camera which has sufficient sensitivity in low-light environments without using
gain. In general, cameras which have CCD imagers with large surfaces are more
light-sensitive than cameras which have CCD imagers with small surfaces.
 Infrared: Another popular way of overcoming difficult environmental lighting conditions is
to use artificial infrared lighting combined with an infrared-sensitive camera with an
infrared pass filter. Retroreflective license plates are particularly suitable for use with
infrared lighting.
o Retroreflectivity is achieved by covering surfaces with a special reflective material
which sends a large portion of the light from a light source straight back along the
path it came from. Retroreflective objects appear to shine much more brightly than
other objects; at night they can thus be seen clearly from considerable distances.
Retroreflectivity is frequently used for road signs, and is also used for different
types of license plates.
 Weather, etc.: Snow, very bright sunlight, etc. may require special configuration of
cameras.
 Plate condition: Vehicles may have damaged license plates. License plates may
occasionally have been damaged deliberately in attempts to avoid detection. Vehicles may
also simply have dirty license plates.
 Camera condition: Camera lenses may accumulate dirt over time.
Physical Positioning of Cameras
When mounting cameras for license plate recognition, bear in mind the following:
 Single-line rule: Mount the camera in such a way that you are able to take an image of a
single line license plate recorded by the camera, and draw a horizontal line that crosses
both the left and right edge of the license plate:
Acceptable mounting
Incorrect mounting
 Plate in image center: Mount the camera in such way that an ideal image of the license
plate is captured when the license plate is in the center of the recorded image.
 Vertical angle: The maximum vertical view angle of a camera used
for license plate recognition is 30 degrees:
 Horizontal angle: The maximum horizontal view angle of a camera
used for license plate recognition is 25 degrees. In most systems the
horizontal angle is somewhere between 15 and 20 degrees.