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
|
|
vehicles stopped; no interlacing |
130 |
vehicles are moving; interlaced |
215 |
||
Single line European plates
|
|
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