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.

TitleLinkWhat it’s really aboutCategoryDateOwner
Apparatus for reading optical informationhttps://patents.google.com/patent/US5591972Strobing IR LEDs at the framerate of the camera, e.g. 30HzALPR feature1995
Illumination Technologies
System for simultaneously imaging vehicles and their license plateshttps://patents.google.com/patent/US6650765B1/enUse of a polarised filter to image the vehicle and the number plate with 2 cams and a single flash at the same timeALPR feature2000JAI
Automated processing method for bus crossing enforcementhttps://patents.google.com/patent/US9741249B2/enVideo analysis for ALPR on a school bus only when the STOP sign is deployed.ALPR feature2011Conduent
Privacy-preserving evidence in ALPR applicationshttps://patents.google.com/patent/US9779284B2/enEncrypt images using the number plate as metadata, so that they can be decrypted only if another image has the same number plate.ALPR feature2013Conduent
Multi-query privacy-preserving parking management system and methodhttps://patents.google.com/patent/US9792301B2/enImage 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.parking2014Conduent
Intelligent automatic license plate recognition for electronic tolling environmentshttps://patents.google.com/patent/US10019640B2/enUsing 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 feature2016Accenture
Methods and systems for confidence-based image processinghttps://patents.google.com/patent/US9100572B2/enUse one camera for quick, low quality images, see it warrants firing up the second, better cam with IR and a tighter field of viewALPR feature2013Xerox
Positional detector device for a vehicular license platehttps://patents.google.com/patent/US6281928B1Detection of license plates in an image using a NN, describes edge detection and Gaussian window.ALPR method1998Umetech
Automated license plate locator and reader including perspective distortion correctionhttps://patents.google.com/patent/US5651075Number plate distortion correctionALPR method1993
Hughes Missile Systems
License plate recognition with an intelligent camerahttps://patents.google.com/patent/US6553131B1/enALPR using a set of filters + a CNN with a 2 layer 100 hidden neurons.ALPR method1999Siemens
Method and system for detection-based segmentation-free license plate recognitionhttps://patents.google.com/patent/US10068146B2/enUse of a combination of CNN, Markov chains and Viterbi decoding to OCR a number plate without character segmentation.ALPR method2016Conduent
Coarse-to-fine cascade adaptations for license plate recognition with convolutional neural networkshttps://patents.google.com/patent/US9785855B2/enTraining of CNN for ALPRALPR method2015Conduent
Method and system for detection and classification of license plateshttps://patents.google.com/patent/US9911055B2/enPre-processing images with a fast, but weak classifier before passing them to a slower, but stronger cassifier for ALPR.ALPR method2016Conduent
Reinforcement learning approach to character level segmentation of license plate imageshttps://patents.google.com/patent/US9213910B2/enReinforced learning for character segmentation to skirt around them without entering the actual character body.ALPR method2013Conduent
Robust character segmentation for license plate imageshttps://patents.google.com/patent/US8934676B2/enCharacter segmentation using vertical histograms, assuming there is white space between the characters.ALPR method2015Conduent
Methods and systems for enhancing the performance of automated license plate recognition applications utilizing multiple resultshttps://patents.google.com/patent/US8781172B2/enUsing front and back plate images to improve confidence and correct for errorsALPR method2012Conduent
Methods and systems for improved license plate signature matching by similarity learning on synthetic imageshttps://patents.google.com/patent/US8588470B2/enGenerate synthetic images of known number plates, e.g. wanted, registered, to speed up matching with real life images using some similarity metric.ALPR method2011Conduent
Method and system for identifying a license platehttps://patents.google.com/patent/US8792682B2/enUse of run-length filter to locate text inside an image.ALPR method2011Conduent
Efficient and fault tolerant license plate matching methodhttps://patents.google.com/patent/US8798325B2/enOCR improvement using similarity of characters and p-tables (probability tables). E.g. O/Q, U/V, etc.ALPR method2012Xerox
Methods and systems for efficient image cropping and analysishttps://patents.google.com/patent/US9569681B2/enCrop 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 method2014Xerox
Video-based vehicle speed estimation from motion vectors in video streamshttps://patents.google.com/patent/US9582722B2/enUses 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 method2012Conduent
System for recognizing the same vehicle at different times and placeshttps://patents.google.com/patent/US6747687Using vehicle features to compute a unique ID for a vehicle instead of doing ALPR.non-ALPR2000JAI
Automatic character recognition systemhttps://patents.google.com/patent/US4567609A/enA generic OCR patent, often cited in ALPR patentsOCR1983US Navy
Vehicle identification, tracking and enforcement systemhttps://patents.google.com/patent/US8937559A business process of recording number plates in a DB for parking.parking2003Avigilon
Image-based vehicle speed estimationhttps://patents.google.com/patent/US9607220B1/enCalculating vehicle speed from multiple frames using a calibrated virtual mesh for distance projections.speed2017VAAS Inc
Vehicle speed monitoring systemhttps://patents.google.com/patent/US8189048B2/enALPR cams and a centrally-located computer for calculating average speed. Includes 2 extra time sources for accuracy.speed2012Neology
Combined laser/radar-video speed violation detector for law enforcementhttps://patents.google.com/patent/US6696978B2/enGetting the number plate and superimposing speed and colour on the image.speed2001Philips
Average speed detection with flash illuminationhttps://patents.google.com/patent/US9641806B2/enDon’t fire the flash unless the vehicle is known to be speeding by the second camera in a 2-camera average speed set up.speed2013Neology
Vehicle speed measurement method and system utilizing a single image capturing unithttps://patents.google.com/patent/US9083856B2/enMeasuring vehicle speed using the size of the number plate and the calibration process for it.speed2012Conduent
Vehicle speed determination via infrared imaginghttps://patents.google.com/patent/US8935082B2/enAccurate speed detection using the tyre point of contact with the ground as the anchor point.speed2012Conduent