[Chicago] OpenALPR - Transformations

Fri Nov 4 15:38:43 EDT 2016

Some links you may find useful below.  I am surprised ALPR doesn't do this already.

The problems reading license plates by humans have resulted in deaths (due to hits on mis-entered license numbers in the context of traffic stops).  I hope you are getting a better feeling of how we need to be careful with the tasks given to our new robotic overlords.

An interesting post from a couple years ago is "How to Build a Kick-Ass Mobile Document Scanner in Just 5 Minutes" (http://www.pyimagesearch.com/2014/09/01/build-kick-ass-mobile-document-scanner-just-5-minutes/) .  It covers sharpening the image, doing a perspective transformation and getting the document ready for OCR (but not the OCR step).

The book "Automate The Boring Stuff With Python" has a chapter on "Manipulating Images" that is online and covers how to do the manipulations with PIL (https://automatetheboringstuff.com/chapter17/).  This would be a good start.  If you are working on your project with Python 3 (if not, why not?) I believe Pillow has the same API.

There have been a number of github projects in the space of preparing scanned documents that I have seen over the years.  Unfortunately I can't find the best ones I remember so here are ones I found today:
Scantailor (https://github.com/scantailor/scantailor) is a large C++ project that appears to be very complete.  ImproveQuality (https://github.com/tesseract-ocr/tesseract/wiki/ImproveQuality) is also a cpp project meant for text scanning.

A mathematically interesting approach to deskewing is documented in http://www.ijstr.org/final-print/dec2013/An-Integrated-Skew-Detection-And-Correction-Using-Fast-Fourier-Transform-And-Dct.pdf where a Fast Fourier Transform is used to determine the skew without pre-analyzing the image to pull out text lines.

Phil Robare

-----Original Message-----
From: Chicago [mailto:chicago-bounces+proba=allstate.com at python.org] On Behalf Of Chris Vinzons
Sent: Thursday, November 03, 2016 2:52 PM
To: chicago at python.org
Subject: [Chicago] OpenALPR - Transformations

Hi,

I'm using OpenALPR to read still license plates, but the thing is that my sometimes that it doesn't read it correctly. I think this is because of the license plate is tilted. Is there a way to untilt it or is there some kind of training data I could do in python?

Thanks

Chris V

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