CA2230428A1 - Vehicle imaging and verification - Google Patents

Abstract

A method of imaging and verifying vehicle data, includes the steps of capturing a digital image of a vehicle; capturing a digital image corresponding with the vehicle's licence plate; conducting optical character recognition on the licence plate to determine the registration number; communicating with a vehicles database to receive information concerning the vehicle matching the registrationnumber; and displaying the image and information for operator verification.
Apparatus for accomplishing the method includes a digital camera, digital image processing apparatus. optical character recognition apparatus. database accessing apparatus, and image and information display apparatus.

Description

24. Fe~. 1998 15:54 P~ILLIPS ORMOI~DE 61 ~ 9~141867 1~. 3~86 ~ 5~31 Vehicle Imaging and Verification This in~/ention relates t~ a method of imaging and verif~ing vehicle ~ata. It relate~ particularly, but not exclusi~ely, to a rnethod which permits an operator to perf~rm real-time verification of imaged vehicles There are various differen~ applications for vehicle imaging. The~e include:
Speed (photoradar) and red Light Cam~ra Operations, Traffic Violation Detection and Proccssing, 120ute Interval Timing, Access Control, In~ersection Control, Long Term Sur~eillance, Car Parks, Incident detectionl and Vehicle Tracking.
The present invention has application ~o all of these area~, although the 0 following discussion ~ill c~ncen~rate particularly on speed and red llght came~as.
Speed and red light cameras in use today are predominantly celluloid film based. Images of infringing vehicles are capt~red on 35mm film and ~ubsequently viewed with filrn viewers or projectors, or alternatively converted into digital form by using any one of a range of digital fiim scanners. An operator identifies thevehicle registration number from the photograph, perhaps using an enlargement of a portion of the image, and a database o~ vehicle registration details is ~hen interrogated to locate other relevant vehicle ~nr~rn~ation, such as make, model and colour. If the information matches the image, an infrinS7eme!nt notice is issued, In ca~ies wherc the image~ are converted into digital form, the registration ~o nurnber may be identihed automatically by an optical character recognition process, s~ch a~ template matching or neural ne~Norks.
Major CC~5t5 associated with traffic camera operations incl~Jdethe processing of film together with the internal co3ts of managing the ~upply, ~andling and archiving of The medium. In jurisdictions where photographs are scanned and proce5sed digitally, the photographic processes are a hindrance to efficient operations, as much of the equipment used is for the sole purpose of trans~ating the film into digital hrm. This is expensive in terms of capital investment, labour and maintenance.
Film processes also introduce delays in the issue af infrin~ement notices.
In one typical jurisdiction, it currently takes about ~ days to recei~le the film, process it and issl~e lhe in~ringement notice Delays of this length or greater are undesirable because It is believed Ihat the eff~ctivcness of a traffic infringement 24. Feb 1998 15:55 PHILLIPS ORM0~DE 61 3 9614186~ ~.3086 P 6~31 notice system as a deterrent i~ in~rersely proportional to the len~th of time between the infringing ac~ and the receipt of the infringement notice.
Another maj~r lirnitation of film is associated wi~h the digital scanning process. ~he conversion of film into digital irnages introduces degradation in image ~uality which often affects the legibility of th~ offending vehicle's licence plate. The consequence is a reduction in the prosecution rate which means productivity deficiencies, 105t revenue, bu~ more importantly, a reduction in the effectil,fen~ss of the overall program.
There is a need for a mcre efficient way of capturing images and verifying o vehicle data.
The present application is rel~ted to applications filed at the same time by the same applicant entitled Ulrnaging Apparatus" (claiming priority from Australian Provisional Application P052~7 filed 24 February 1997) and "Digital Image Processing" (claiming priority from Australian Provisional Application P0~258 filed 24 Fe~rua~ 1997). The contents of those applications are hereby incorpor~ted herein by reference.
Summary of the Invention According to the present invention, there is provicied a method of imaging and veri~ying vehicle data, in~luding the steps Of:
2n (a) capturing a digital image of a vehicle;
(b) capturing a digital image corresponding with the ~ehicle's licence plate;
~ c) conductin~ optical character recognition on ~he licence plate to deterrnine the registration number;
~5 (d) communicating ~vith a ~ehicles database to receive information concerning the vehicle matching the regi~tration number; and (e) dispiaying the image ~nd information for operator verification.
In one preferred arrang~ment, steps ~a), (b) and (c) be perf~rrne~ at the location of the digital imaging apparatus. This can result in a significant reduction 3~ in the amount ~f digital in~ormation which mugt ~e retained, as a low resolution irna~e of the vehicle ~oget~er with a high resolution Image of the licence plate 24. Feb 1998 15:55 PHILLIPS ORMO~DE 61 ~ 96141867 ~o 3086 P 7/~1 may be sufficient, depending upon the regulatory requirements of the particular ~urisdiction. Moreover, these are steps which take significant tinle in present processing operations, and erflGiency wilt be improYe~ if they can be cornpletedbefore operator intervention is required.
s In thi~ arrangernent, all of ~teps ~a) to (c) and (e) may ~e performed at the location of the digital irn~ging apparatus. Thi& arrangernent is particularly ~uibble for situations where the imaging apparatus is located in a c~r wi~h an operator. All of step~ (a) to (d) can be performed automati~ally before the results are displayed to the in-car operator, ~ho verifies that the licence number identified by the optical character recognition does indeed match the licence plat~ on ~he ima~e, and also that the vehicle details from the vehicle database match the vehic~e image. In some jurisdictions, an infringement notice can then be issued immediately. In other jurisdictions, independent verifi~ation by another op~rator i~
required bef~re the notice can be s~nt. In either event, considerable proce~singtirne is saved, and the c~mera operator's time is used more ef~iciently.
In another preferred arrangernent, steps (c) to (e). and possibly also step (b) are perFormed at one or rno~e sites remote from the carnera site at which step (a) is performed. This arrangemen~ is particularly suitable for ~xed deployrnen~s such as red-light cameras and ~or jurisdictions in which it is not necess~ry to have 2~ an opsrator on-site when images are taken. This arrangement allows from a central control room fr~m ~hich operators supervise the operation of multipl~
cameras remotely by interfacing with carneras by rn~ans of serial communîcati~nssuch as telephone, ISDN, fibre optics, Internet, etc The bulk of tlle processingmay still be p~rforrned on site, ~vith the operator verifying the outputs and issuing manual commands.
The step of r~apturing a digital image of the vehicle may be done in any suitable manner. Most digital irnaS3in~ i~i done usin~ chars~e coL~pled devices (CC~s), ~nd it is preferred that Ccas be used. Imaging may be done by means of commonly available CCDs. More preferably, higher resolution imaging is achieved usin~ a high-resolution single CC~, ;;alternatively, the imaging may involve segmenting the image into an array of sub-images. each of which is detected by one of an array of CCD detectors. and the sub-images may be 24. Feb. 1998 15:56 PHILLIPS ORMO~DE 61 3 96141867 ~ 3086 P 8/31 recombined by digital processing techniques. as described in the afore-mentioned co-pending patent application entitled "Imaging Apparatus".
Ordlnary currently available v~deo Gameras use CCDs which deliver an analog signal with a limited line resolution, Iypically around 600 lines or less. This signal can be digitised and produces an image resolution ~vhich is high enough to obtain an ~verall image of a vehicle, but not high enough for the vehicle's licence plate to be legible in ~he image. It is sufFicient for ~tep (a) above to hav~ a low resolution image of ~he vehicle, but step ~b) ab~ve requires a high resolllticn irn~ge of at least the licence plate.
o The step o~ capturing a digital im~ge corresponding with the Yehicle's licence plate may be done in any suitable manner. This may involvo taking two digital photographs at the same time with two camerac, one a wide-angle photograph to GaptUre the vehicle and surrounding scene, and ~ne with ~ zoorn lens to captur~ the vehicle's licence plate. This method relies on ~sSumptions li conCerning the standard position of the licence plate in a photograph in order to establish the ali~nment of the zo~rn camera, and it is l~nreliable if the infringing vehicle is of non-standard size or shape or is movlng in an ~nexpected directionor non-centrally in the traffic lane.
In some jurlsdictions, particularly those in which vehicles are required ~o carry licenoe plates on the b~ck but not on the front, two images are In any event necessary, one from the front of the vehicle to identify the Yehicle and possibly also the dri~/er, and one frorn the back to identify the licence plate.
An alt~rna~ive to taking two photographs sîmultaneously is to take one wide-angle photograph as soon as the infrlngernent is detected, and then to use a 2s high-speed zoom t~ cap~ure an irnage of the vehicle's licence pl;3te region.However, this approach requires assumptions to be made about the predicted standard position of the licence plate at a predete~mined time after the first photograph has been taken, and it i5 therefore less reliable than the simultaneous photographs technique.

3~ A further problern with the use of standard video cameras in capturing images is the low dynamic range available in digitised images. Bright spots on adark image, sucl~ as a retro-renecti~ liGence plate in an image capt~red at night, tend to "burn out", so that the licenc~g plate is not legible. C)ark spots on a bright 24. Feb 1998 15:56 PHILLIPS ORMO~DE 61 3 96141867 ~o 3086 P 9~31 imase, such as t~le driver in a vehicle photographed on a sllnny day may be so dark that the drlver is not recognisable. Moreover, the low dynamic range of typical vide~ carneras usually makes jT necessary to provide a slow shutter speed for taking dark images ~uch as night-time ph~t~graphs, and this results in blurring of the licence plat~ details due to rTlovement of the vehicle.
It is therefore preferre~ that the digital image corre~ponding ~ith the vehicle's licence plate be a high resolution image ~ith high dynamlc range. It is further preferred that the liccnce pli~te ima~e be part of a larger high-resolution image ~rhich covers a region large enou~h to capture the: licence plate even if the lo licence plate appears in a region different from that expected by standard a~umptions. It is espe~ially preferred that ~he digital image of the vehicle captured in step (a) above b~ a high-resolution imaç~e, and the licence plate digital image of step (b) be obtained by extracting the licence plate regiS;~n from the high-resaluti~n vehicle irnage.
s Extraction may be based on a common region of all images. For ex~rnple,~he apparatus could be set up in such a way that a \/ehicle licence plate appears in the exact centre of each irnage. This can be accomplished rnore easily if secondary vehicle po~ition inforrnation is provided. For red light enforcement this information may be provi~ed by induction loops placed ~lnder the road surFace in0 each lane. When a vehicle in~ir,gC3 a red light, it passes over an inductive l~op that has been placed on or ~bout th~ stop line. The ind-lctive loop senses a magnetic disturbance and repor~s this event t~ the cam~ra~s control unit. When the vehicle crosses a second loop approxil,.dtely 3 rnetres frcm the first ~ideally located in ~he cross walk area) the camera c~ntrol unit calculates the vehi~le ~peed and triggers the camera if the vchicl~ 0xceeds a preset threshold Since each lane is equipped with its own set of loops the carnera con~rol unit i6 able to determine the relative vehicle positi~n.
For speed detection, a r~dar sy~tem may be coupled with a range finding device such as a laser which profiles the vehicle as it enters the radar beam. The o r~dar can provide the vehicle speed, while the laser provides ~he relative distance from which lane information can be gathered. Since the laser is actually pr~filing the vehiGIe, i~ has the ability to deterrnine the exact position of either the front or the ~ack of t~e vehicle, delaying ~he carnera trigger until the optimum vehicle 24. Feb 1998 15:57 PHILLIPS ORMO~DE 61 3 96141867 ~o. 3~86 P 10/31 position is achieved One ~uch de~ice is AWA's VSL (Vehicle Speed Laser-radar).
Alternatively, extraction may be based on a pattern in the image being recognised as a licence plate. Almost all licence plates are retro-reflective, and licence plates can often be recognised as bright spots on the images, particularly when the images are taken under dark lighting Gonditi~ns vvith th~3 aQ~istance of a flash unit which i~ in line with the camera. A llcence plate is usually distinguishable from other bright spots such as ~ehicle headlights because of its shape. Standard computer pattern reco~nition techniques can be used, and the o operator Gan be given an opport~nity to sp~ci~ the licence plate area if the cornputer fails t~ rec~gnise the cc~rrect area. Further preferred features of digieal imag~ pro~essing ~teps are described in the afore-mentioned co-pendin~ patent application entitled "Digital Irnage Processing". ::
~ he step of conducting optical character recognition may be done in any suitable rnanner. Optical character recognition may be done according t~
standard OCR techniql~es. The operator may be given an opportunity to specify ~he correct registration number if the computer cannot complete optical character reco~nition or if the recognilion is incorrect.
The step of communicating with a vehicles database may be done in any 20 suitabl~ manner. CommlJnication may be by means of radi~, telephone lines, fibre optics lines, dedica~ed data lines, or any other suitable communication medium The database may even be stored on the operator~s computer îf security and priYacy laws for the Particular j~risdiction permit T~le step of displaying the image and information for operator verification ;;~5 may be ~ccomplish~d in any s~litab~e nlanner. It is preferred that the information disp~ayed include the image of the vehjcle, a close-up view of the area recc~gnised by the cornputer as the licence plate, the registration number identifled by theOCR ~tep, and vehicle make, model and colour information provided by the database. Other information ~uld also be displayed, depending upon the 30 particular regulatory requirements of the jurisdicti~n.
The method of the invention n~ay further include the step of storing the digi~al image and other information in a cornputer storage rnedium for further reference and for eviaentiar~ and archival purposes. It is preferred that the image 24 Feb 1998 15:57 PHI~LIPS ORMO~DE 61 3 96141867 ~o.3086 P 11~31 be compressed before storage using a co~pression technique which results in little or no loss of im~ge information. It ~s also preferred that the storage medi~m incorporate rneans for securing against tampering or unaulhorised access.
The method of the inverltian mlay fl~rthe- include the step ~f capturing and 5 sloring a video buFfer being a video reGording of the vehicle and surrounding scene for a few seconds before andlor after ~he even~ which giv~s rise to the taking of the photograph. Such a video buffer can be helpful in proving or di~proving a traffic violation.
Apparatus for accornpli~hing the method of th~3 inv~ntion may include a o di~ital camera, di~ital irnage processing app~r~tus, optical character recognition apparatu~, database accessing ~pparat~s, and imaç~e and information display apparatus.
As an optional enhancement to ~uch apparatus, there may be pro~ided a high frequency sound sensor to detect such incidents as screeching tyres ar ~s breaking glass and ~utomatically activate the digital camera to ~ive supervisin3 operator~ early warning of a traffiG incident.
The invention \Nill now ~e described in more detail by reference to the drawings. It is to be ~nderst~od that the par~icularity of the drawings does not supersede the generality of the preceding description of the invention.
Clescription of tho Drawings Figure t Is a flow diagram of an embodiment o~ the method of the pre~ent invention Figures 2 and 3 are schematic illustrations of vehicles on a four-lane road, demonstrating the maxirnum ~nd minim~.~m di9tances of vehicle from imaging ap~aratus.
Figure ~ strates the concept of dividing an image into sub-image~ in accordance with an aspect of the invention.
Figure 5 illustrates the same concept, with the image segmented into a 5 array of sub-images.
~0 Figure 6 is a simplified schematic diagram of image-segmentation or bearn-splitting apparat~s.

24. Feb. 1998 15:58 PHILLIPS ORMOI~DE 61 3 96141867 1~. 3086 P 12/31 Figure 7 is a diagrarn of a more detailed preferred beam-splltting arrangement using lenses.
Fig~re 8 is a speed camera photograph illu~Srating an over-exposed licence plate.
s Figure 9 is a histogram 3howing intensity distributions of pixels in a speed camera photograp~.
Figure 10 is a graph showing a rnapping of an 8-bit image to a 4-bit im~ge in a wa~r which enhances licence plate legibility.
Figure 1 1 is the imag~ of Figure 8 af~er proce~sing according to the ~o mapping technique of Figure 1 O.
Figl~re 12 is a block diagram af a data processing arrangement according to one embodiment of the inver~tion.
Referring firstly to Figure 1, there is shown a rneth~d ~f imaging and ~erifying vehicle data according to the invention, involYing s~reral steps. The first step consists of capturing a digital image of a vehicle. ~s shown in morc detail in Figures 4 to 7, and descrfbed hereafter, one preferred method for acc~mplishing this step i5 by first splitting the irnaç~e into multiple sub-imayes, detectinE~ the sub-images using an array of CCDs~ and then recombining the image data digitally.
~he next step shown in Figure 1 involves capturing a digital irnage ~o correspondin~ wi~h the vehicle's licence plate. In a preferred arrangement this in~olves extracting the relevant reyion from the vehicle di~ital image This step i5 explained in more detail herea~er with respect to Figures 8 to 11. The next stepcomprises conducting optical character recognition on the licence plate to determine the registration number. This is done according to kno~n OCR
techniques. The next step involves Gommunicating ~vith a vehicles database to reGeive inforrnation concerning the vehicle matching the registration number. This step is also done according to standard database interrogation and cornmunications techniques; and the final step consists of displaylng the image and information for operator ~erifi~ation. Th~3 display may be on ~ny suitable ]~ computer display de~ice, such as a cathode ray tube, liquid crystal display, or g~s plasma display.

24. Feb. 1998 15:58 PHILLIPS ORMO~DE 61 3 96141867 ~. 3~86 P 13~31 According to standard design specifications for a traffic camera, the camera must provi~e an optical perforrnance such that a vehicle travelling away from the carnera ~n a faur lane road is still in focus. The lîcence plate at the rear of the vehicle must be machine readable. This position is Illustrated in Figure 2, which shows a stationary vehicle 1 which has radar and carnera apparatus, and ~Ivhich is parked immediately adjacent the edge 2 of a four-lane road 3. ~ moving VehjGIe 4 i5 travelling away from the camera irl the fourth or furthest lane 5 from the camera. The maximum field cf view. th~t is the focal depth, is determined byFigure Z togetherwith the 2quation:-10 Camera Fo~ ax ~ Total Road Width I Radar Carnera Offse~sin(Radar Arlgle - ~Radar Fo\~ an~le / 2)) (3-5 1 3.5 1 3 5 ~ 3.5 ~ 1.76 sin(20 - ~1012)) - 60 ~8~m lS Figure 3~ which i]lustrates the rnethod for de~ermininy the minimum-field of view, showc a ~tationary ~/ehicle 6 which has radar and camera apparatus and which is parked immediately ~djacent the ~dge 7 of a road 8. A moving vehicle is tra~rellin~ alonh road 8 towards the camera. The minimum camera field of vie~,v, that is the focal depth, can be determined as illustrated in Fi~ure 3 to~ether with ~o the equation:-Camera FoVmjn = Mir)imum Road Width ~ Radar Camera Offset sin(Radar Angle ~ (Radar FoV angle / 2)) (3.5 + 1.75) sin(20 + (10 / 2)) = 10 06m From these constraints it is possible to calculate the minimum and maximum Licence Piate sizes~ and the digital re~olution nece~sary tc~ provide adequate image quality.
Capt4nng a Digital Ima0e The Charge Coupled Device or CCD is a image acquisition device Gapable of con~erting light energy emitted or reflected from an object into a electricalcharge which is directly propor~ional to the entering light~s intensity. The CCD is in theory capable of providing excellent dynamic res~lution t~ut unfortunately due the rnanufacturin~ complexity and current world demand, can only delive~ Iimited spatial density or reso~ution.

~4. Feb 1998 15:59 P~ILLIPS ORM0~DE 61 3 96141867 ~ 3086 P 14~31 Core utilisation of CCC~ technology i5 in the home video market which demands ~nly a low resolution of the order 752x582 (standard Hi 8 Sony palm camera) pixels. Although special order CCDs can be rnanufactured to deiiver higher resolution, they pro~e to be economically prohibitive because of their special-order nature and opera~ing requirement~.
However, with the utilisation of optiGal ~cience, the objective image can be broken into srnaller components as illustra~ed in Figures 4 and 5 and distributed to several CCDs arranged in a special array in order ~o provide the necessary resolution. As each sub-image i~ distributed to each CCD, a central processor o can digitally build the original im~ge, much like putting a Jig-~aw together. Using ~pecial image processing al~orithms, joins can be sm~othed removing any evidence o~ image di~ruption. Figure 4 shows a complete ima~e 10, broken up into nine separate sub-images 11.
An ad~Janced optical sy~tem is used to distribute the primary image into 25 l5 separate images with minimum disto~tion and k~ss to each individl~al CCD. It ha~
been found that a ~ x 5 array produces a slJitable final resolution. In addition to the 25 CCDs, a low resolution image of the entire primary image will be capturedby utilisin~ another CCD of the same type. ~he 26'h CCD is positioned such that it doe~ n~t interfere with any of the 25 ~ptical path~. I=igure 5 shows an arrangement in which an image is broken up into a 5 x 5 array of sub-images 12, with a low-resolution cornplete image 13 being captured at the same tirne.
Figure 6 is a sirnplined diagr;lm of the image separation or beam-splitting step. Thero are various dif~er~nt beam-splitting techniques which can be used, including partial mirrors, lenses and a parallel array of coherent fibre optic ~s bundles Lig~lt which forms the image to be captured passes through objective lens 14. The li~ht ~hen passes ~hrough beam splirter 15 and is split into separ;~te sub-image~. These sub-image~ are then detected by CCD elements 1~3, one CCD
det~cting each sub-image.
Figure 7 is a more detailed diagram of a preferred lens arrangement. Light J0 Passes into the imaging apparatus through the obJe~tive lens 17, which has eight elements. It then passes thro~gh a beam splitter or partially silvered mirror 18which allows approximately 96% of the incident light to pass and refl~-;t~
approximately 4% of the i~cident light through lenses 19 to form a low resolution 24. Feb 1998 15:59 PHILLIPS ORMO~DE 61 3 96141867 ~ 3086 P 15~31 image on CCD 20. The majority of ~he light then passes throu~h field lens 21 andthree-elenlent collimator Z2 and finally through an array of focussing lenses 23bef~re f~rming separate sub-images on an array of CCDs 24 To eliminate any evidence of sub-image distribution over the CCD array, a small percentage of adjacent o- neighbouring CCD sub-ima~3es are overlaid ont~
each C~D. rhis allows f~r seamless reconstruction and image processing techniques ta smooth any c3pt~re difFerence resulting frorn chrom~tic and inten~ity loss.
Experim~ntation has re~ealed that suitable ima~ing re~uits can be obtained using a 5 x 5 array of Sony CCDs of type ICX075~ which have a resolution of 7a4 x 5~4 pixels, a pixel si2e of 8 micron by 8 micron, and a dynamiG
range of 65dB. More recent experimentation with the ~oon-to-be-released hlgh resolution Sany CC~s of type ICX20~, which have a res~lution of 1434:x 10~0 pixels, of ~uhich 139~ x 1040 pixels are useable, a pixel size of 4 micron by 4 micron, and a dynamic range c~ 70dR h~s reve~led that satisfactory results can be achieved using a 2 x 2 array of such CCDs. This is now the preferred imaging apparatus, because it is much easier to construct a 2 x 2 ~rray than a 5 x 5 array.
The preferred imaging apparatLIS i~ described in more detail in theaforementioned ~-pending patent application entitled 'Imaging Appararusn.
Processing th~ Digital Image Data There are several aspects to processing the digital image data. The first aspect involves matching data'frorn ad3acent CCD~ to recreate the total image This is accornpli~hed according to standard pattern-recognition and matching techniques. Other asp~cts include selection of an area of partiGular interest for ~5 high-resolution viewing (the licence plate region), image data modification (particLJlarly to compensate for over-exposure caused by the actfon of a flash unit on retro-reflective licence plates). and image data cornpression Wh~n images are taken in dark conditions usin~ a flash unit which is on the same axis a~ the camera, the brightest area of a speed and red-light violation image is on the retro reflective licence plate area, the car head lamp6 or otherwhite areas. This means that these areas reflect most light energy, causing higher intensi~y liglnt to enter the cam~3ra. This can result in over exposure vvhen devel~ping ths image, makin~ the licence plate details unreadable. Figure 8 24. Feb 1998 16:00 PHILLIPS ORMO~DE 61 3 9614186~ ~.3086 P 16~31 shows a typical speed camera photo3raph, with a dark background ~rea 25 and the licence plate area 25 over-exposed.
Figur~ 9 shows a typical llistogr~r~ of the intensities of individual pixels in a speed violation image. Because o~ its almost universally retro-reflective nature, 5 the Licence Plate i~ almost always l~ d at the high 10-20% of the in~ensity graph 27 for images ta~en in dark conditions using a flash unit. In order to make the Licence Plate readable, a preferrYd ~eature of the present inYention provides for the intensity values of the pixels in the licence plate are~ to be decreased.
Because the image information relatin~ to the background scene and the ~o vehicle (other than the licence plate) i-~ of less relative importance in a vehicle ima~e, such information can be cornpres~ed ~o a significant extent. Gompression can occur at the same time as the Licence Plate is rrade readable. ~y way of example, the image may include 8-bit intensity infor~natic~n (~55 levels of intensity). This can be converted to a 4-bit image (16 level~ of brightness), inwhich 6 levels (the high 10-20~/a Of intensity levels) are a~ ned to the Licenc0Plate and 10 leYels (the low 80-90% of intensity levels) are ~ssigned to the rest of the image. An algonthm for accomplishing this is described bel~w Comp~te the highest intensity (Yrnax) of the image. The lowest intensity is assumed t~ be zero.
~o Calculate 10-20% high inten~ity range from the Ymax.
Cornpute the rnagnit~de of each divisi~n for Scene image (10 levels) -Scene Div and License Plate image (6 levels) - LP Div.
Convert each pixel of the image to inten6ity Y.
For each pixel Y.
2s if the intensity is in the "Scen~" range, divide the intensity with the Scene Div .
if the in~ensity is in the "Licence Plate'' range, divide the intensity with the LP Div.
For the purpose of displaying the 4-bit image with a graphics program, the resulting 4-~it image is tc1 conver~ back to an equivalent 8-bit image by multiplying the con~ersion f~ctor (255/16).
~0 Forexample If Ymax - 240.
20~ intensity of the high end is 2~0 ~ .8 = 132 If a calc~lated Y intensity is 1 B0 (in lo~ intensity range) , then the equivalent level is = 18~ / Sccne Div.

24. Feb. 1998 16:0~ PHILLIPS ORM0~DE 61 3 96141867 ~ 3086 P. 17~31 If a calculated Y intensity is 230 (in hi~h intensity range), then the equivalent le~/el is ~ (~240 - 230) I LP ~iv ) + 10.
The above example is illustrated in Figure 1~, which is a graph mapping ~riginal 8-bit image Intensit~ levels (~55 leve~s) to compressed 4-bit (16 levels~
irnage intensity levels. Figure 11 is a pllotograph showin~ the image of Figure 8 after the image compression proc~ss. Some detail has been lost from the b~ckground scene 25, but the blown up view of the lîcence plate region 26 shows the licence plate as clearly legible.
The above example relates to an application in which it is impor~ant ~o o reduce the intensi~y of pixels i~ a region to ensure clarity of that region. Similar techniq~es are also applicable t~ enhancing ~he intensity of pixels in a region. For exarnple, in some jurisdictions it i~; necessary tcl be able to identify the driver before a traffic infringement notice can be issued. In rnl~st cases, the ;~river's features will be darl~er than most of the imags. ~y selectively increasing the l~ intensity of pixels in the region of the image where the driver's face appears, the driver rnay be more readily reco~nised.
It is of course not necessa~ in all cases for image intensity manipulation to occur Image compr~ssion is, however, important because of th~ enom ous sizes of files generated by digital images whiG~ have sufficient res~lution to enable ~o accurate rec~gnition of llcence plate details. In order for the invention to be practicable, a re~sonable number of images must be able to fit onto a computer storage device ~such as a r~m~va~le hard disk), and image data must be capable of bein~ transferred through computer processing stages at a reasonable rate Compression may occur before or after the image has been viewed by an 25 operator. It is preferred that t~e operator view the image after compression so that the imag~ quality has been ascertained.
In compressing an image flle, it is important ~o store a high-resolution image of the licence plate area but the rest of the image can usually be stored at lower resolution (depending upon regulato~ requirei "ents for the particular 30 juriçdiction). Thus there is scope for reducing image size both by rsducing pixel intensity information (the number of different intensity le~JQls, as discussed above) and by reducing the numb~r of pixels per unit area (other than in the licence plate area). As mentioned pre\~iously, the licence plate area iS preferably identified by 24.Feb 1998 16:~1 PHILLIPS ORMO~DE 61 3 96141867 ~o.~086 P 18~31 1'1 intelligent recognition technique~s. Where, as in the presently preferred forms of t~le invenlion, t~e high resolution image is generated from a 2 x 2 array ~r a 5 x 5 array of sub-inages, it is preferred that an additional CCD capture a lower-resolution overall image. This image can provide the basis of tlle l~u/er-resolution 5 background ~cene image which i~ ~tor~d along vvith the higher-resolution licence plate image which is extracted from tl~e higher resolution overall inlage.
It is preferred that the data procesçing steps include a form of data encryption to preserve data security and prevent unauthorised access. The compression techniques selected may encompass an aGceptable encryption o aigorithm; altern~tively1 encryption may be applied after compre~sion. It is possible to apply encryption before cc~mpression, but this m~y adver~ely affect cornpres~ion effciency.
A block diagram for the data ~eGtion of the CCD system according'to one emb~dirnent of the invention i~ shown in Fig 12. In this arrangem~nt, sub-imagesare detected by the array of CCDs 28. Data from e~ch CCD 2~ is passed to a corresponding analog fr~nt-end processor 29, and data fronl a group of processors 29 is combined and passed into analog multiplexers 30~ and from there via analog to digital convert~3rs 31 to data compre6sor 32, and on to a computer for further processing via PCI bus interfaGe 33.
~o Other techniques for image pr~t:es~ing ~re discussed in the afore-mentioned co-pendin~ patent ~pplication entitled "Digital Image Processingn.
It is to be understood that vario~s alterations, additions and/or modifications may be made to the parts previously described without departing from the ambit of the invention.

Claims (11)

1. A method of imaging and verifying vehicle data, including the steps of:
(a) capturing a digital image of a vehicle;
(b) capturing a digital image corresponding with the vehicle's licence plate;
(c) conducting optical character recognition on the licence plate to determine the registration number;
(d) communicating with a vehicles database to receive information concerning the vehicle matching the registration number: and (e) displaying the image and information for operator verification.

2. A method according to claim 1 wherein the step of capturing a digital image corresponding with the vehicle's licence plate involves extracting a region of the digital image captured in the step of capturing a digital image of a vehicle.

3. A method according to claim 1 or claim 2 wherein steps (a), (b) and (c) are performed at the same location.

4. A method according to claim 3 wherein step (e) is also performed at the same location.

5. A method according to claim 1 or claim 2 wherein step (a) is performed at one location and steps (c) to (e) are performed at a different location.

6. A method according to claim 1 or claim 2 wherein the step of capturing a digital image of a vehicle involves capturing multiple sub-images and subsequently combining them into a high resolution image using digital processing techniques.

7. A method according to claim 1 or claim 2 wherein the step of capturing a digital image corresponding with the vehicle's licence plate involves digitally adjusting the intensities of pixels in the image to improve legibility.

8. A method according to claim 1 or claim 2 further including the step of storing the digital image and other information in a computer storage medium forfurther reference or for evidentiary or archival purposes.

9. A method according to claim 8 further including the steps of capturing and storing a video image buffer being a video recording of the vehicle for a few seconds before and/or after the performance of step (a).

10. Apparatus for accomplishing the method of claim 1 or claim 2 including a digital camera, digital image processing apparatus, optical character recognition apparatus, database accessing apparatus, and image and information display apparatus.

11. Apparatus according to claim 10 further including a high frequency sound sensor to detect such incidents as screeching tyres or breaking glass and automatically activate the digital camera to give supervising operators early warning of a traffic incident.