1. Enable the inspection tool

To enable the inspection tool right click on the view of the GatekeeperAxon. A pop up box will appear. Choose ANPR.  An overlay of ANPR information will be drawn on the image.

Overlay not visible

If the overlay is not displayed it means there is no ANPR result.

•Blue squares
Sometimes a blue square is drawn around the license plate. It means the ANPR engine has found a region of interest but was not able to read a license plate.
When the overlay displays many blue squares many regions of interests are found. Reducing background noise by cropping the image will speed up the processing speed of the AnprAxons. Frame rate will increase. Make sure the license plate will be in scope for all the desired vehicle positions.  
Select ROI and reduce background IDSAxon, read more
Select ROI and reduce background USBCameraAxon, read more

•License plate too small
The license plate is too small (recommended width is 100-350 pixels).
When a license plate is visible but not recognized zooming in or out and adjusting focus will do the trick most of the times.

•License plate too bright
If the license plate is over lit, adjust exposure and gain in the IDSAxon or change the sequencing.

•ANPRAxons not properly configured
Check the information about the ANPRAxon for this topic.

•Minimum width of license plate not set.
Check chapter, Setting minimal license plate width, how to do this.

•ANPRThresholdAxon not configured properly
Check chapter, Optimizing ANPR threshold, to solve this.

2. The inspection tool explained

On the top of the screen Anpr0  8 fps is seen. ANPR0  is the name of the ANPRAxon the frame is processed by and it’s individual framerate. Next to the framerate the Anpr result is displayed that is found for this image.

White characters above the lp

Around the license plate live information about recognition is displayed.  The white letters above the license plate. represent the cut outs of the characters before interpretation. After interpretation the result of recognition is found at the top of the screen.

Green number at the right top

Next to the ANPR result highlighted in green two numbers are displayed. The top number is the width in pixels of the license plate.  In order to  recognize a license plate it’s width must be between 100 and 300 pixels. The second number shows the height in pixels. This number must be above 20. If the numbers are out of bounds they will turn red. Zoom and focus levels need to be adjusted.

The number within the white box

The number within the white box informs us about the average brightness of the background of the license plate. It illustrates the strength of the LED lights. When the value drops under 50 recognition will be more difficult.  When the slider of the LEDs is moved the number will change.

The two numbers in red

The two numbers in red (show it) represent the sharpness of the image. The first number is the sharpness at the moment. The second number the higher sharpness measured so far in this image. When the first number is lower sharpness can be adjusted by rubber banding the license plate (dragging a square over the license plate with your mouse, show it). Sharpness will be recalculated. Remember that the number represents the highest value measured so far. Environmental circumstances can be changed in a way that for this moment the highest value can not be reached.

The green number on the left

Moving over to the green number on the left. This number represent the degree of tilting. This value needs to be beneath 10.

3. Inspection tool schematic