Milestone LPR 1.0 - Manual (Page 32)

Milestone XProtect
®
LPR 1.0 Administrator's Manual
www.milestonesys.com 32 About LPR cameras
About LPR cameras
LPR differs from other kinds of video surveillance. Normally, you choose cameras based on their
ability to provide the best possible images for viewing by the human eye. However, when choosing
cameras for LPR, only the small part of the images which contains the actual license plate is
important.
Choose the right camera
When optimizing the small part of the images containing the actual license plate, keep some basic
features in mind:

Resolution: Choose cameras which have a sufficient resolution.

Dynamic range: Choose cameras that have a sufficient dynamic range. A camera’s dynamic
range determines, among other things, its sensitivity in low- and high-light conditions, how it
reacts to changing light conditions, and how sensitive it is to infrared lighting.

Shutter speed: Choose cameras that give you the ability to set a shutter speed (see "Lens
and shutter speed" on page 33) fitting your requirements.

Undesired features: Choose cameras that give you the ability to disable image enhancement
techniques (see "Unwanted camera features" on page 37), such as auto-gain and
contrast/contour enhancement. For LPR, you generally want your images as raw as possible.

Lenses: Choose cameras that have —or let you choose—lenses which are suitable for your
required camera resolution and your external lighting conditions. For example, when infrared
lighting is used it is preferable to also use a lens with an infrared pass filter or at least a lens
which is compensated for infrared light. Otherwise you get a focus shift when the environment
gets dark. To achieve a better dynamic range for your camera it is sometimes recommended
to use a lens with auto-iris.
o Iris is the adjustable opening (a.k.a. aperture) used for controlling the amount of light
coming through a lens. Iris thus has a significant effect on the exposure of images.

Infrared cameras: Only choose infrared camera if conditions allow. If a license plate has
several background colors, there might be situations where infrared cameras cannot be used.
On the plate shown below, the red color makes it impossible to read the white letters on the
upper half of the plate when recorded with an infrared camera.
Left: With normal camera.
Right: With infrared camera.