Milestone Analytics 2.2 Dacolian LPR - Manual (Page 39)

Milestone XProtect Analytics 2.2 – Dacolian LPR; Administrator’s Manual
www.milestonesys.com Page 39 Camera Tips & Tricks
Shutter time in seconds Max. vehicle speed in
kilometers per hour Max. vehicle speed in
miles per hour
1/50 4 2
1/100 9 5
1/200 18 11
1/250 22 13
1/500 45 27
1/750 68 41
1/1000 90 55
1/1500 136 83
1/2000 181 111
1/3000 272 166
1/4000 363 222
Physical Environment
When mounting and using cameras for license plate recognition, bear in mind the following
environmental factors:
 Much light: Too much light in the environment can lead to overexposure or smear.
o Overexposure is when images are exposed to too much light, resulting a in a burnt-
out and overly white appearance. To avoid overexposure it is recommended that
you use a camera with a high dynamic range and/or use an auto-iris lens. 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.
o Smear is an effect leading to unwanted light vertical lines in images; it is frequently
linked to slight imperfections in cameras’ CCD imagers (the sensors used to
digitally create the images). In general, CCD imagers with large surfaces are less
sensitive to smear than CCD imagers with small surfaces. Cameras with CMOS
imagers (a different type of sensors, with a higher noise immunity) are less
sensitive to smear than cameras with CCD imagers.
License plate image with smear
 Little light: Too little environmental or external lighting can lead to underexposure.
o Underexposure is when images are exposed to too little light, resulting in a dark
image with hardly any contrast. When auto-gain cannot be disabled (for more
information about gain, see Undesired Camera Features on page 42) or when you
are not able to configure a maximum allowed shutter time for capturing moving
vehicles (see Lens & Shutter Speed on page 38), too little light will initially lead to