Milestone LPR 1.0 - Manual (Page 36)

Milestone XProtect
®
LPR 1.0 Administrator's Manual
www.milestonesys.com 36 About LPR cameras

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 LPR is 30°:

Horizontal angle: The maximum horizontal view angle of a camera used for LPR is 25°. In
most systems the horizontal angle is somewhere between 15° and 20°.

Blocking objects: Avoid possible blocking objects in the view path of the camera, such as
pillars, barriers, fences, gates, etc. Remember that barriers, gates, etc. are likely to be
movable between different positions.
Resolution
The term pixels per stroke is used to define a minimum requirement for LPR. The following illustration
outlines what is meant by stroke:
Because the thickness of strokes depends on country and plate style, measurements like pixels/cm or
pixels/inch are not used.
The resolution for best LPR performance should be at least 2.7 pixels/stroke.

For single line US plates (plate width 30.5 cm; stroke width around 0.7 cm) this typically means
that the plate width in the image must be at least 130 pixels.