A License Plate Recognition and Speed Detection System - Index of

width is only 5/16” will be 3 pixels wide ((5/16)/(5*12)*640 pixels). This may or may not be
enough pixels depending on the object character recognition algorithms being used. On the other
hand, having too many pixels can cause a negative effect. The more pixels an image contains, the
longer it will take image processing routines to process the image. A balance must be met.
It should also be noted that camera images should be clear and sharp with little noise.
Cameras that output digital signals such as DTV or computer protocol signals such as IEEE 1394
generally have better image quality than cameras that output analog signals such NTSC or PAL.
It is desirable for an LPR customized camera to output a clear, sharp image to increase the
accuracy of software image processing and character recognition routines.
Also, depending on how the video camera is implemented, it should either have a trigger
port or a very high frame rate. The trigger port is used to signal the camera when to take a
picture. The camera trigger port is connected to the trigger component of the LPR system that
senses when a car is present. If the same video camera is also being used as the trigger
component then it should have a very fast frame rate. This will ensure an image of the vehicle is
captured before passing the camera.
A summary of desirable LPR video camera characteristics is given in the table below.
When a video camera contains these characteristics, a high quality image of the intended license
plate will be captured.
Table 2 LPR Video Camera Characteristics
Characteristic Desired Value
Long pass filter All visible wavelengths of light are
blocked.
Telephoto Lens
Powerful enough to image license
Magnification
Telephoto Lens Field of
View
plate characters at a distance
Wide enough to capture license plate
when vehicle travels within its lane
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