ALPR / ANPR patents in plain English

Automatic License Plate Recognition (ALPR or ANPR) was first tried by UK Police Scientific Development Branch with EMI Electronics from Hays and later Computer Recognition Systems (CRS) from Wokingham.

It’s been 33 years and the ALPR/ANPR field is exploding. So who’s got interesting patents in that area?

We will look into the protected IP going back to those days and earlier for the OCR part.

Name search

  • Xerox: 46 (many sold to Conduent)
  • Conduent: 15
  • PIPS: 6
  • 3M: 4 (sold to Neology, spun off as PIPS)
  • Vysionics: 1 (they took over the original CRS from Wokingham)
  • Jenoptik: 0 (they took over Vysionics)

One of the most prolific inventors named on ALPR / ANPR patents is Vladimir Kozitsky, originally from Xerox and now with Conduent.

Interesting patents

This is, by any means, not an exclusive list. There are hundreds more patents from this and related areas, specially OCR and Machine Learning. There is actually very little novelty or invention in those patents. ALPR is just a subset of OCR technology that is being transformed by use of neural nets and other enabling technologies.

Title Link What it’s really about Category Date Owner
Apparatus for reading optical information https://patents.google.com/patent/US5591972 Strobing IR LEDs at the framerate of the camera, e.g. 30Hz ALPR feature 1995
Illumination Technologies
System for simultaneously imaging vehicles and their license plates https://patents.google.com/patent/US6650765B1/en Use of a polarised filter to image the vehicle and the number plate with 2 cams and a single flash at the same time ALPR feature 2000 JAI
Automated processing method for bus crossing enforcement https://patents.google.com/patent/US9741249B2/en Video analysis for ALPR on a school bus only when the STOP sign is deployed. ALPR feature 2011 Conduent
Privacy-preserving evidence in ALPR applications https://patents.google.com/patent/US9779284B2/en Encrypt images using the number plate as metadata, so that they can be decrypted only if another image has the same number plate. ALPR feature 2013 Conduent
Multi-query privacy-preserving parking management system and method https://patents.google.com/patent/US9792301B2/en Image search by number plate where the number plate is converted into an intermediate format using Fisher Kernel or some other statistical tool and matched to the same of the images. parking 2014 Conduent
Intelligent automatic license plate recognition for electronic tolling environments https://patents.google.com/patent/US10019640B2/en Using data from ALPR cams in other locations to determine the probability of the vehicle being in the area to take into account as one of confidence parameters. E.g. the same number plate was sighted 100km away 15 min ago. ALPR feature 2016 Accenture
Methods and systems for confidence-based image processing https://patents.google.com/patent/US9100572B2/en Use one camera for quick, low quality images, see it warrants firing up the second, better cam with IR and a tighter field of view ALPR feature 2013 Xerox
Positional detector device for a vehicular license plate https://patents.google.com/patent/US6281928B1 Detection of license plates in an image using a NN, describes edge detection and Gaussian window. ALPR method 1998 Umetech
Automated license plate locator and reader including perspective distortion correction https://patents.google.com/patent/US5651075 Number plate distortion correction ALPR method 1993
Hughes Missile Systems
License plate recognition with an intelligent camera https://patents.google.com/patent/US6553131B1/en ALPR using a set of filters + a CNN with a 2 layer 100 hidden neurons. ALPR method 1999 Siemens
Method and system for detection-based segmentation-free license plate recognition https://patents.google.com/patent/US10068146B2/en Use of a combination of CNN, Markov chains and Viterbi decoding to OCR a number plate without character segmentation. ALPR method 2016 Conduent
Coarse-to-fine cascade adaptations for license plate recognition with convolutional neural networks https://patents.google.com/patent/US9785855B2/en Training of CNN for ALPR ALPR method 2015 Conduent
Method and system for detection and classification of license plates https://patents.google.com/patent/US9911055B2/en Pre-processing images with a fast, but weak classifier before passing them to a slower, but stronger cassifier for ALPR. ALPR method 2016 Conduent
Reinforcement learning approach to character level segmentation of license plate images https://patents.google.com/patent/US9213910B2/en Reinforced learning for character segmentation to skirt around them without entering the actual character body. ALPR method 2013 Conduent
Robust character segmentation for license plate images https://patents.google.com/patent/US8934676B2/en Character segmentation using vertical histograms, assuming there is white space between the characters. ALPR method 2015 Conduent
Methods and systems for enhancing the performance of automated license plate recognition applications utilizing multiple results https://patents.google.com/patent/US8781172B2/en Using front and back plate images to improve confidence and correct for errors ALPR method 2012 Conduent
Methods and systems for improved license plate signature matching by similarity learning on synthetic images https://patents.google.com/patent/US8588470B2/en Generate synthetic images of known number plates, e.g. wanted, registered, to speed up matching with real life images using some similarity metric. ALPR method 2011 Conduent
Method and system for identifying a license plate https://patents.google.com/patent/US8792682B2/en Use of run-length filter to locate text inside an image. ALPR method 2011 Conduent
Efficient and fault tolerant license plate matching method https://patents.google.com/patent/US8798325B2/en OCR improvement using similarity of characters and p-tables (probability tables). E.g. O/Q, U/V, etc. ALPR method 2012 Xerox
Methods and systems for efficient image cropping and analysis https://patents.google.com/patent/US9569681B2/en Crop images in increments to see if they are overcropped. Not clear where the cropping should start and how do you know you are cropping a plate or some other text? ALPR method 2014 Xerox
Video-based vehicle speed estimation from motion vectors in video streams https://patents.google.com/patent/US9582722B2/en Uses vector motion data from the encoded video stream (result of the compression algorithm) to locate vehicles (basically blobs of pixels) and estimate speed. It is not as accurate and further processing is done on the decompressed video if needed. ALPR method 2012 Conduent
System for recognizing the same vehicle at different times and places https://patents.google.com/patent/US6747687 Using vehicle features to compute a unique ID for a vehicle instead of doing ALPR. non-ALPR 2000 JAI
Automatic character recognition system https://patents.google.com/patent/US4567609A/en A generic OCR patent, often cited in ALPR patents OCR 1983 US Navy
Vehicle identification, tracking and enforcement system https://patents.google.com/patent/US8937559 A business process of recording number plates in a DB for parking. parking 2003 Avigilon
Image-based vehicle speed estimation https://patents.google.com/patent/US9607220B1/en Calculating vehicle speed from multiple frames using a calibrated virtual mesh for distance projections. speed 2017 VAAS Inc
Vehicle speed monitoring system https://patents.google.com/patent/US8189048B2/en ALPR cams and a centrally-located computer for calculating average speed. Includes 2 extra time sources for accuracy. speed 2012 Neology
Combined laser/radar-video speed violation detector for law enforcement https://patents.google.com/patent/US6696978B2/en Getting the number plate and superimposing speed and colour on the image. speed 2001 Philips
Average speed detection with flash illumination https://patents.google.com/patent/US9641806B2/en Don’t fire the flash unless the vehicle is known to be speeding by the second camera in a 2-camera average speed set up. speed 2013 Neology
Vehicle speed measurement method and system utilizing a single image capturing unit https://patents.google.com/patent/US9083856B2/en Measuring vehicle speed using the size of the number plate and the calibration process for it. speed 2012 Conduent
Vehicle speed determination via infrared imaging https://patents.google.com/patent/US8935082B2/en Accurate speed detection using the tyre point of contact with the ground as the anchor point. speed 2012 Conduent