Undefined function 'readLetter' for input arguments of type 'logical'.

%NUMBERPLATEEXTRACTION extracts the characters from the input number plate image.
f=imread('car3.jpg'); % Reading the number plate image.
f=imresize(f,[400 NaN]); % Resizing the image keeping aspect ratio same.
g=rgb2gray(f); % Converting the RGB (color) image to gray (intensity).
g=medfilt2(g,[3 3]); % Median filtering to remove noise.
se=strel('disk',1); % Structural element (disk of radius 1) for morphological processing.
gi=imdilate(g,se); % Dilating the gray image with the structural element.
ge=imerode(g,se); % Eroding the gray image with structural element.
gdiff=imsubtract(gi,ge); % Morphological Gradient for edges enhancement.
gdiff=mat2gray(gdiff); % Converting the class to double.
gdiff=conv2(gdiff,[1 1;1 1]); % Convolution of the double image for brightening the edges.
gdiff=imadjust(gdiff,[0.5 0.7],[0 1],0.1); % Intensity scaling between the range 0 to 1.
B=logical(gdiff); % Conversion of the class from double to binary. 
% Eliminating the possible horizontal lines from the output image of regiongrow
% that could be edges of license plate.
er=imerode(B,strel('line',50,0));
out1=imsubtract(B,er);
% Filling all the regions of the image.
F=imfill(out1,'holes');
% Thinning the image to ensure character isolation.
H=bwmorph(F,'thin',1);
H=imerode(H,strel('line',3,90));
% Selecting all the regions that are of pixel area more than 100.
final=bwareaopen(H,100);
% final=bwlabel(final); % Uncomment to make compitable with the previous versions of MATLAB®
% Two properties 'BoundingBox' and binary 'Image' corresponding to these
% Bounding boxes are acquired.
Iprops=regionprops(final,'BoundingBox','Image');
% Selecting all the bounding boxes in matrix of order numberofboxesX4;
NR=cat(1,Iprops.BoundingBox);
% Calling of controlling function.
r=controlling(NR); % Function 'controlling' outputs the array of indices of boxes required for extraction of characters.
if ~isempty(r) % If succesfully indices of desired boxes are achieved.
    I={Iprops.Image}; % Cell array of 'Image' (one of the properties of regionprops)
    noPlate=[]; % Initializing the variable of number plate string.
    for v=1:length(r)
        N=I{1,r(v)}; % Extracting the binary image corresponding to the indices in 'r'.
        letter=readLetter(N); % Reading the letter corresponding the binary image 'N'.
        while letter=='O' || letter=='0' % Since it wouldn't be easy to distinguish
            if v<=3                      % between '0' and 'O' during the extraction of character
                letter='O';              % in binary image. Using the characteristic of plates in Karachi
            else                         % that starting three characters are alphabets, this code will
                letter='0';              % easily decide whether it is '0' or 'O'. The condition for 'if'
            end                          % just need to be changed if the code is to be implemented with some other
            break;                       % cities plates. The condition should be changed accordingly.
        end
        noPlate=[noPlate letter]; % Appending every subsequent character in noPlate variable.
    end
    fid = fopen('noPlate.txt', 'wt'); % This portion of code writes the number plate
    fprintf(fid,'%s\n',noPlate);      % to the text file, if executed a notepad file with the
    fclose(fid);                      % name noPlate.txt will be open with the number plate written.
    winopen('noPlate.txt')
%     Uncomment the portion of code below if Database is  to be organized. Since my
%     project requires database so I have written this code. DB is the .mat
%     file containing the array of structure of all entries of database.
%     load DB
%     for x=1:length(DB)
%         recordplate=getfield(DB,{1,x},'PlateNumber');
%         if strcmp(noPlate,recordplate)
%             disp(DB(x));
%             disp('*-*-*-*-*-*-*');
%         end
%     end
else % If fail to extract the indexes in 'r' this line of error will be displayed.
    fprintf('Unable to extract the characters from the number plate.\n');
    fprintf('The characters on the number plate might not be clear or touching with each other or boundries.\n');
end
end

error:

numberPlateExtraction
Error using fprintf
Invalid file identifier.  Use fopen

[per isakson]

Most likely

    fid = fopen('noPlate.txt', 'wt');

fails to open the file. Put a breakpoint at

    fprintf(fid,'%s\n',noPlate);

and check. (Read the help on fopen.)

&nbsp

And what does

    which readLetter -all

return?

[Praveen kumar]

i am asking the error on the line letter=readLetter(N); Undefined function 'readLetter' for input arguments of type 'logical'

[per isakson]

So what does

which readLetter -all

return?

&nbsp

And why did you include

"error:"

numberPlateExtraction
Error using fprintf
Invalid file identifier.  Use fopen

in your question?

[Praveen kumar]

Unable to extract the characters from the number plate. The characters on the number plate might not be clear or touching with each other or boundries. >> still no output plzz help

[per isakson]

Do you have a file named readLetter.m?

[Praveen kumar]

Yeah there

[Walter Roberson]

Is the current error still about readLetter? If so then is the readLetter that you have on your MATLAB path?

 which readLetter

Or is the error you are working on now the one about invalid file identifier? If so then please show us the result of

pwd

Answer 1

[Walter Roberson]

readLetter is part of http://www.mathworks.com/matlabcentral/fileexchange/44088-car-license-plate-reader or http://www.mathworks.com/matlabcentral/fileexchange/40426-vehicle-number-plate-recognition . You need to download one of those two .zip files, and unzip them into a convenient directory that is not under your MATLAB installation directory, and then use the MATLAB command pathtool to add the directory to the MATLAB path; remember to tell pathtool to "save" the path afterwards. After that, your code will be able to find readLetter .