Openalpr: detect the background color of the plate

[laplasz]

Is it posible to detect the background color of the lincese plate?
in my country there is a meaning of each color, for example:
blue - diplomat
yellow - taxi
green - zerro emission
white - regular

So would be great to detect the type of the plate by background color as well

[matthill]

OpenALPR doesn't do that out of the box, but it's possible. The simplest way to do this would be to convert the plate area to HSV and use the hue (within a range) to determine what type of color the plate is. Here's an example (used to detect flesh color from an image):
http://shervinemami.info/blobs.html

This won't work very well at night.

[laplasz]

Ok so I am newbie in image recognition - but perhaps if I have the area stored in AlprPlateResult then I need to convert that image and set the right hue, saturation and value to able to detect one of the plate color..

[gstiebler]

Showing a histogram of hue values for different types of plates may help you determine the range of hue that should be used for each kind of plate.

[matthill]

Yes, you could do this after the plate has been recognized by OpenALPR. We provide coordinates for the 4 corners of the plate. So, you could grab the plate coordinates, crop out your plate from that, and run a hue analysis to get the color.