matlab-lpr

Introduction

A simple license plate recognition project using Matlab.

First Step: Preparing image for finding plate location.

• Read image and filter with median filter to remove salt and pepper noise.
• Find a threshold value and binarize the image using this threshold value.
• Crop an area that license plate can exist.
• Remove boundary and small objects in image.
• Using imclose and imfill functions mark the plate area

%**************************************************************************
% First Step - Read 640x480 car image and remove unnecessary objects
%**************************************************************************
img = imread('image02.jpg');
BWC1 = imcrop(img,[0 200 640 240]);
img1=rgb2gray(img);
img1=medfilt2(img1,[3 3]);      %Median filtering the image to remove noise
threshold = graythresh(img1);
BW = im2bw(img1,threshold);
BWC2 = imcrop(BW,[0 200 640 240]);   %Plate Location Assumption
BW1 = imclearborder(BWC2,8);
BW2 = bwareaopen(BW1,1500,8);
se = strel('rectangle',[10 100]);
BW3 = imclose(BW2,se);
BW4 = imfill(BW3,'holes');
[L,NUM] = bwlabeln(BW4,8);
if NUM==1
    BW5 = (L==1);
end
if NUM==2
    BW5 = (L==2);
end

Second Step: Plate localization and cropping the plate

• Using regionprops function find the center of plate and get coordinates of license plate location.
• Using imcrop function crop the license plate.

%**************************************************************************
% Second Step - Find license plate coordinates and crop it from the image
%**************************************************************************
L2 = bwlabel(BW5);
STATS = regionprops(L2, 'Centroid');
xc = round(STATS.Centroid(1,1));
yc = round(STATS.Centroid(1,2));
plate_x = xc - 110;
plate_y = yc - 27;
BW6 = imcrop(BW5,[plate_x plate_y 230 55]);
BW7 = imcrop(BWC1,[plate_x plate_y 230 55]);

Third Step: Character segmentation and extraction

• Using bwlabel function label each character on the license plate.
• Using regionprops BoundingBox function extract each character from the license plate.

%**************************************************************************
% Third Step - Segment and extract each character from the license plate
%**************************************************************************
plate=rgb2gray(BW7);
plate=medfilt2(plate,[3 3]);    %Median filtering the image to remove noise
threshold = graythresh(plate);
BWP = im2bw(plate,threshold - 0.1);
IBWP=imcomplement(BWP);
BWP2=imclearborder(IBWP,8);
CBWP = bwareaopen(BWP2,90,8);
%Character segmentation (isolating each character from the image)
[L3,NUM2] = bwlabeln(CBWP);
for i=1:NUM2
    object = bwlabel(L3==i);
    stats2 = regionprops(object,'BoundingBox');
    bounds = round(stats2.BoundingBox);
    characters{i} = imcomplement(imcrop(object,bounds));
end
%Now we have all characters in characters{} array

Final Step: Optical Character Recognition (OCR)

• OCR part uses correlation algorithm to identify chacters and numbers.
• Matlab’s corr2 function compares our extracted characters with the predefined template characters.

%**************************************************************************
% Final Step - Character Recognition (OCR)
% Diego Barragán Guerrero
% diegokillemall@yahoo.com
% Private Technical University of Loja (Ecuador)
% http://www.matpic.com/MATLAB_OCR.html
%**************************************************************************
%Resize all characters in to 42x24 standard size
%CREATE TEMPLATES
%Letter
A=imread('templates/A.bmp');B=imread('templates/B.bmp');
C=imread('templates/C.bmp');D=imread('templates/D.bmp');
E=imread('templates/E.bmp');F=imread('templates/F.bmp');
G=imread('templates/G.bmp');H=imread('templates/H.bmp');
I=imread('templates/I.bmp');J=imread('templates/J.bmp');
K=imread('templates/K.bmp');L=imread('templates/L.bmp');
M=imread('templates/M.bmp');N=imread('templates/N.bmp');
O=imread('templates/O.bmp');P=imread('templates/P.bmp');
Q=imread('templates/Q.bmp');R=imread('templates/R.bmp');
S=imread('templates/S.bmp');T=imread('templates/T.bmp');
U=imread('templates/U.bmp');V=imread('templates/V.bmp');
W=imread('templates/W.bmp');X=imread('templates/X.bmp');
Y=imread('templates/Y.bmp');Z=imread('templates/Z.bmp');
%Number
one=imread('templates/1.bmp');  two=imread('templates/2.bmp');
three=imread('templates/3.bmp');four=imread('templates/4.bmp');
five=imread('templates/5.bmp'); six=imread('templates/6.bmp');
seven=imread('templates/7.bmp');eight=imread('templates/8.bmp');
nine=imread('templates/9.bmp'); zero=imread('templates/0.bmp');
%*-*-*-*-*-*-*-*-*-*-*-
letter=[A B C D E F G H I J K L M N O P Q R S T U V W X Y Z];
number=[one two three four five six seven eight nine zero];
character=[letter number];
templates=mat2cell(character,42,[24 24 24 24 24 24 24 ...
    24 24 24 24 24 24 24 ...
    24 24 24 24 24 24 24 ...
    24 24 24 24 24 24 24 ...
    24 24 24 24 24 24 24 24]);
save ('templates','templates')
%**************************************************************************
license_plate=[];%Storage matrix word from image
for i=1:NUM2
    reschars{i} = imresize (characters{i}, [42 24]);
    charim = reschars{i};
    comp=[];
    load templates
    for n=1:36
        sem=corr2(templates{1,n},charim);
        comp=[comp sem];
    end
    vd=find(comp==max(comp));
    %---------------------------------------------------------------------
    if vd==1
        letter='A';
    elseif vd==2
        letter='B';
    elseif vd==3
        letter='C';
    elseif vd==4
        letter='D';
    elseif vd==5
        letter='E';
    elseif vd==6
        letter='F';
    elseif vd==7
        letter='G';
    elseif vd==8
        letter='H';
    elseif vd==9
        letter='I';
    elseif vd==10
        letter='J';
    elseif vd==11
        letter='K';
    elseif vd==12
        letter='L';
    elseif vd==13
        letter='M';
    elseif vd==14
        letter='N';
    elseif vd==15
        letter='O';
    elseif vd==16
        letter='P';
    elseif vd==17
        letter='Q';
    elseif vd==18
        letter='R';
    elseif vd==19
        letter='S';
    elseif vd==20
        letter='T';
    elseif vd==21
        letter='U';
    elseif vd==22
        letter='V';
    elseif vd==23
        letter='W';
    elseif vd==24
        letter='X';
    elseif vd==25
        letter='Y';
    elseif vd==26
        letter='Z';
        %*-*-*-*-*
    elseif vd==27
        letter='1';
    elseif vd==28
        letter='2';
    elseif vd==29
        letter='3';
    elseif vd==30
        letter='4';
    elseif vd==31
        letter='5';
    elseif vd==32
        letter='6';
    elseif vd==33
        letter='7';
    elseif vd==34
        letter='8';
    elseif vd==35
        letter='9';
    else
        letter='0';
    end
    license_plate=[license_plate letter];
end
sprintf('Okunan Plaka : %s.',license_plate)
license_plate=[];%Clear 'license_plate' variable

Plotting all outputs.

%**************************************************************************
% Obtained Outputs
%**************************************************************************
figure
subplot(1,3,1)
imshow(img),title('Coloured Car Image')
subplot(1,3,2)
imshow(img1), title('Gray Level Median Filter')
subplot(1,3,3)
imshow(BW),title('Binary Image')
%**************************************************************************
figure
subplot(2,3,1)
imshow(BWC2), title('Plate Area Assumption')
subplot(2,3,2)
imshow(BW1),title('Clear Border')
subplot(2,3,3)
imshow(BW2),title('Clear Small Objects')
subplot(2,3,4)
imshow(BW3),title('Close Areas')
subplot(2,3,5)
imshow(BW4),title('Fill Areas')
subplot(2,3,6)
imshow(BW5),title('Plate Location')
%**************************************************************************
figure
subplot(1,2,1)
imshow(BW6),title('Cropped Area')
subplot(1,2,2)
imshow(BW7),title('Cropped Plate')
%**************************************************************************
figure
subplot(3,2,1)
imshow(BW7),title('Coloured Car Plate')
subplot(3,2,2)
imshow(BWP),title('Binary Car Plate')
subplot(3,2,3)
imshow(IBWP),title('Complement Car Plate')
subplot(3,2,4)
imshow(BWP2),title('Clear Borders')
subplot(3,2,5)
imshow(CBWP),title('Clear Plate')
%**************************************************************************
figure
for i=1:NUM2
    subplot(1,8,i)
    imshow(characters{i})
end
figure
for i=1:NUM2
    subplot(1,8,i)
    imshow(reschars{i})
end
%**************************************************************************
%-----------------end of script--------------------------------------------

This project was developed for the digital image processing course at the university.

Thank you.