MATLAB Answers


how to extract the given type of number plates and the characters ?

Asked by Ehtesham Ul Hossain Khan on 9 Nov 2018 at 18:25
Latest activity Commented on by Image Analyst
on 10 Nov 2018 at 20:57
I am working on license plate recognition, but I am stuck on how to develop the code for extracting or localizing the rectangular shape of a number plate from the car image .


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1 Answer

Answer by Image Analyst
on 9 Nov 2018 at 20:47
 Accepted Answer

Try the code below. It works for the given image. You'll need to adapt it to handle cars of different colors and different size plates, but at least this gives you a start on the idea.
clc; % Clear the command window.
close all; % Close all figures (except those of imtool.)
workspace; % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 16;
% Get the name of the image the user wants to use.
baseFileName = 'anpr3.jpg';
folder = pwd;
fullFileName = fullfile(folder, baseFileName);
% Check if file exists.
if ~exist(fullFileName, 'file')
% The file doesn't exist -- didn't find it there in that folder.
% Check the entire search path (other folders) for the file by stripping off the folder.
fullFileNameOnSearchPath = baseFileName; % No path this time.
if ~exist(fullFileNameOnSearchPath, 'file')
% Still didn't find it. Alert user.
errorMessage = sprintf('Error: %s does not exist in the search path folders.', fullFileName);
% Read in demo image.
rgbImage = imread(fullFileName);
% Get the dimensions of the image.
[rows, columns, numberOfColorChannels] = size(rgbImage)
% Display image.
subplot(2, 2, 1);
imshow(rgbImage, []);
axis on;
caption = sprintf('Original Color Image\n%s', baseFileName);
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.
% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0.05 1 0.95]);
% Get rid of tool bar and pulldown menus that are along top of figure.
% set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off')
[mask, maskedRGBImage] = createMask(rgbImage);
% Get the convex hull to get rid of boundary noise (wiggles).
mask = imfill(mask, 'holes');
% Count the blobs
[~, numBlobs] = bwlabel(mask);
% Display the mask image.
subplot(2, 2, 2);
caption = sprintf('Color Segmentation Image : %d blobs', numBlobs);
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
axis on;
% Measure sizes of blobs.
props = regionprops(mask, 'Area', 'Solidity');
allAreas = [props.Area];
subplot(2, 2, 4);
histogram(allAreas, 50);
grid on;
title('Histogram Of Areas', 'FontSize', fontSize);
% Extract only blobs in the 5000-10000 pixel size range
mask = bwareafilt(mask, [1000, 7000]);
% Remove blobs touching border because we assume license plate will be in the field of view, not off of it.
mask = imclearborder(mask);
% Measure bounding boxes of blobs.
props = regionprops(mask, 'BoundingBox');
allBB = [props.BoundingBox];
allWidths = allBB(3:4:end);
allheights = allBB(4:4:end);
aspectRatios = allWidths ./ allheights
% Take only thos where aspect ratio in in the right range - around 2 so in the range 1.5 - 3.
goodBlobIndexes = find(aspectRatios > 1.5 & aspectRatios < 3)
% Extract that/those blobs only:
labeledImage = bwlabel(mask);
mask = ismember(labeledImage, goodBlobIndexes);
% Take the convex hull
mask = bwconvhull(mask);
% Display the mask image.
subplot(2, 2, 3);
title('Final Plate Found', 'FontSize', fontSize, 'Interpreter', 'None');
axis on;
% Mask the image using bsxfun() function to multiply the mask by each channel individually.
maskedRgbImage = bsxfun(@times, rgbImage, cast(mask, 'like', rgbImage));
% Display the mask image.
subplot(2, 2, 4);
title('Final Plate Found (RGB Image)', 'FontSize', fontSize, 'Interpreter', 'None');
axis on;
function [BW,maskedRGBImage] = createMask(RGB)
%createMask Threshold RGB image using auto-generated code from colorThresholder app.
% [BW,MASKEDRGBIMAGE] = createMask(RGB) thresholds image RGB using
% auto-generated code from the colorThresholder app. The colorspace and
% range for each channel of the colorspace were set within the app. The
% segmentation mask is returned in BW, and a composite of the mask and
% original RGB images is returned in maskedRGBImage.
% Auto-generated by colorThresholder app on 09-Nov-2018
% Convert RGB image to chosen color space
I = rgb2hsv(RGB);
% Define thresholds for channel 1 based on histogram settings
channel1Min = 0.004;
channel1Max = 0.998;
% Define thresholds for channel 2 based on histogram settings
channel2Min = 0.000;
channel2Max = 0.102;
% Define thresholds for channel 3 based on histogram settings
channel3Min = 0.399;
channel3Max = 1.000;
% Create mask based on chosen histogram thresholds
sliderBW = (I(:,:,1) >= channel1Min ) & (I(:,:,1) <= channel1Max) & ...
(I(:,:,2) >= channel2Min ) & (I(:,:,2) <= channel2Max) & ...
(I(:,:,3) >= channel3Min ) & (I(:,:,3) <= channel3Max);
BW = sliderBW;
% Initialize output masked image based on input image.
maskedRGBImage = RGB;
% Set background pixels where BW is false to zero.
maskedRGBImage(repmat(~BW,[1 1 3])) = 0;


Show 1 older comment
What version of MATLAB do you have? If you have R2016a or earlier, you'll have to add
function NumberPlateRegion()
as the first line, and get rid of the final "end" at the last line. Or else put the function createMask() into a separate m-file, createMask.m, as the test harness code at the beginning.
i was using 2016,after installing 2017 it's working well. Thank you Sir. What should I do for character segmentation, as all the characters are written in Bengali language.

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