Plate width recommendations

Mount the camera so that the ideal snapshot of the license plate is captured when the license plate is in the center or lower half of the image:

Take a snapshot and make sure that the requirements to stroke width and plate width as described below are fulfilled. Use a standard graphics editor to measure the amount of pixels. When you start the process of reaching the minimum plate width, begin with a low resolution on the camera, and then work your way up in a higher resolution until you have the required plate width.

Stroke width

The term pixels per stroke is used to define a minimum requirement for fonts that should be recognized. 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.

Plate width

Plate type

Plate width

Setup

Minimum plate width (pixels)

Single line US plates

 

  • plate width 12 inches
  • stroke width around ¼ inches

vehicles stopped; no interlacing

130

vehicles are moving; interlaced

215

Single line European plates

 

  • plate width 52 cm
  • stroke width around 1 cm

vehicles stopped; no interlacing

170

vehicles are moving; interlaced

280

If vehicles are moving when recorded, and an interlaced camera is used, only a half of the image can be used (only the even lines) for recognition compared with a camera configured for stopped vehicles and no interlacing. This means that the resolution requirements are almost double as high.

© 2019 Milestone Systems A/S