Milestone Analytics 2.2 Dacolian LPR - Manual (Page 42)

Milestone XProtect Analytics 2.2 – Dacolian LPR; Administrator’s Manual
www.milestonesys.com Page 42 Camera Tips & Tricks
Unwanted Camera Features
When configuring cameras for license plate recognition, bear in mind the following:
 Automatic gain adjustment: One of the most common types of image interference
caused by cameras is gain noise.
o Gain is basically the way in which a camera takes a picture of a scene and
distributes light into it. If light is not distributed optimally in the image, the result is
gain noise.
Controlling gain requires that complex algorithms are applied, and many cameras have features for
automatically adjusting gain. Unfortunately, such features are not always helpful for cameras used
for license plate recognition. It is therefore recommended that you configure your cameras’ auto-
gain functionality to be as low as possible. Alternatively, disable the cameras’s auto-gain
functionality altogether.
License plate image with gain noise
Tip: In dark environments, gain noise can also be avoided when your external lighting is sufficient.
 Automatic enhancement: Some cameras use contour, edge or contrast enhancement
algorithms to make images look better to the human eye. However, such algorithms can
interfere with the algorithms used in the license plate recognition process. It is therefore
recommended that you disable cameras’ contour, edge and contrast enhancement
algorithms whenever possible.
 Automatic compression: High compression rates can have a negative influence on the
quality of license plate images. When a high compression rate is used, more resolution (see
page 41) is required in order to achieve optimal license plate recognition performance. If
JPEG compression is used, it will have almost no negative influence on license plate
recognition performance, as long as the images are saved with a JPEG quality level of 80%
or above, and images have normal resolution, contrast and focus as well as a low noise
level.
Left: License plate image saved with a JPEG quality level of 80% (i.e. low
compression); acceptable
Right: License plate image saved with a JPEG quality level of 50% (i.e. high
compression); unacceptable