Milestone Analytics 2.2 Dacolian LPR - Manual (Page 37)

Milestone XProtect Analytics 2.2 – Dacolian LPR; Administrator’s Manual
www.milestonesys.com Page 37 Camera Tips & Tricks
Camera Tips & Tricks
Choosing the Right Cameras
License plate recognition 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 use with license plate recognition, only the small part of the
images which contains the actual license plates is important.
Therefore, keep some basic features in mind when choosing cameras for use with license plate
recognition:
 Resolution: Choose cameras which have a sufficient resolution.
 Dynamic range: Choose cameras which 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 which give you the ability to set a shutter speed fit for
your requirements. See also Lens & Shutter Speed on page 38.
 Undesired features: Choose cameras which give you the ability to disable image
enhancement techniques, such as auto-gain and contrast/contour enhancement. For
license plate recognition, you generally want your images as raw as possible. See also
Undesired Camera Features on page 42.
 Lenses: Choose cameras which have—or lets 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.
Contrast
When determining the right contrast for license plate recognition, consider the difference in gray
value (when images are converted to 8-bit grayscale) between the license plate’s characters and
the license plate’s background color:
Good contrast