Why am I getting this error?

function letter=readLetter(snap)

load NewTemplates
snap = imresize(snap,[42 24]); 
rec=[ ];

for n=1:length(NewTemplates)
    cor=corr2(NewTemplates{1,n},snap); 
    rec=[rec cor]; 
end

ind=find(rec==max(rec));
display(ind);

% Alphabets listings.
if ind==1 || ind==2
    letter='A';
elseif ind==3 || ind==4
    letter='B';
elseif ind==5
    letter='C';
elseif ind==6 || ind==7
    letter='D';
elseif ind==8
    letter='E';
elseif ind==9
    letter='F';
elseif ind==10
    letter='G';
elseif ind==11
    letter='H';
elseif ind==12
    letter='I';
elseif ind==13
    letter='J';
elseif ind==14
    letter='K';
elseif ind==15
    letter='L';
elseif ind==16
    letter='M';
elseif ind==17
    letter='N';
elseif ind==18 || ind==19
    letter='O';
elseif ind==20 || ind==21
    letter='P';
elseif ind==22 || ind==23
    letter='Q';
elseif ind==24 || ind==25
    letter='R';
elseif ind==26
    letter='S';
elseif ind==27
    letter='T';
elseif ind==28
    letter='U';
elseif ind==29
    letter='V';
elseif ind==30
    letter='W';
elseif ind==31
    letter='X';
elseif ind==32
    letter='Y';
elseif ind==33
    letter='Z';
    %*-*-*-*-*
% Numerals listings.
elseif ind==34
    letter='1';
elseif ind==35
    letter='2';
elseif ind==36
    letter='3';
elseif ind==37 || ind==38
    letter='4';
elseif ind==39
    letter='5';
elseif ind==40 || ind==41 || ind==42
    letter='6';
elseif ind==43
    letter='7';
elseif ind==44 || ind==45
    letter='8';
elseif ind==46 || ind==47 || ind==48
    letter='9';
else
    letter='0';
end
end

The error I am getting is

Not enough input arguments.

Error in Letter_detection (line 4)

snap = imresize(snap,[42 24]);

[Walter Roberson]

When you press the green Run button, what is your expectation about where MATLAB should look to find the value of the variable snap ? For example is your expectation that MATLAB will load the contents of the file snap.mat and use that?

[Abhiram M V]

in the above code we have created a function named letter which gives us the alphanumeric output of the input image from class ‘alpha’ by using command ‘Letter_detection()’. And then load the saved templates by using command load ‘NewTemplates.

After that, we have resized the input image so it can be compared with the template’s images by using the command ‘imresize(filename,size)’. Then for loop is used to correlate the input image with every image in the template to get the best match.

A matrix ‘rec’ is created to record the value of correlation for each alphanumeric template with the characters template from the input image, as shown in the below code,

cor=corr2(NewTemplates{1,n},snap);

Then ‘find()’ command is used to find the index which corresponds to the highest matched character. Then according to that index, corresponding character is printed using‘if-else’ statement.

[Walter Roberson]

Well, ideally.

But you are pressing the green Run button to run the code. Your code needs a value for snap . Where you are you expecting that MATLAB is going to look for the value of snap when you press the green Run button?

[Abhiram M V]

I referred to this website for the code

https://circuitdigest.com/tutorial/vehicle-number-plate-detection-using-matlab-and-image-processing

[Walter Roberson]

Uh huh. So look at the section there

Number Plate Detection

Here is the third and final code file named Plate_detection.m

and observe that it contains the code

for i=1:count
   ow = length(Iprops(i).Image(1,:));
   oh = length(Iprops(i).Image(:,1));
   if ow<(h/2) & oh>(h/3)
       letter=Letter_detection(Iprops(i).Image);
       noPlate=[noPlate letter]
   end
end

Notice that line

       letter=Letter_detection(Iprops(i).Image);

that invokes the function Letter_detection, passing in a sub-image extracted from the plate image.

The code that circuitdigest provided does not invoke Letter_detection by clicking on the green Run button, and you should not be clicking on the green Run button in file Letter_detection either. You should be invoking Plate_detection. It is okay to switch to Plate_detection.m and press the green Run button there because that is a script rather than a function.

[Abhiram M V]

ok got it. Thank you.

Answer 1

[Walter Roberson]

By the way:

letters = 'AABBCDDEFGHIJKLMNOOPQRRSTUVWXYZ1234456667889990';
if ind > length(letters)
    letter = '0';
else
    letter = letters(ind);
end

[Abhiram M V]

What exactly is ind?

[Walter Roberson]

ind=find(rec==max(rec));

according to the code you posted.

[JIAHONG LIM]

Hi Roberson, may I know why some letter need two ind to determine but some only need one?

if ind==1 || ind==2

letter='A';

elseif ind==3 || ind==4

letter='B';

elseif ind==5

letter='C';

[Walter Roberson]

I do not know. It looks liike the person who posted the code had two templates for some letters.

[JIAHONG LIM]

Is it stored in the 'NewTemplates' file which created by the person who posted and unchangable? Thank you.

https://circuitdigest.com/tutorial/vehicle-number-plate-detection-using-matlab-and-image-processing

The link below is the full code of the program. For the first part which is template creation, the code showed the A-Z and 1-0 are listed once. Why there are some letters need two ind to determine it? Thank you very much for your explanation and patience.

[Walter Roberson]

The NewTemplates .mat appears to have contained a cell array of template data, in which some of the letters had two different templates.

It would have been better if the NewTemplates .mat file also contained a list of which cell entry contained which letter... but either it did not contain that or else the person who posted the code did not understand how to make use of the information.

[JIAHONG LIM]

Okay, I got it. Thank you very much. You are excellent and pro!

[Walter Roberson]

This is taken from https://circuitdigest.com/tutorial/vehicle-number-plate-detection-using-matlab-and-image-processing which has a mismatch between the template building code and the template data file.

The characters that have two entries are the ones that have a "hole" in them. In the first version of the template, the hole is empoty, and in the second version of the template, the hole is filled.

[JIAHONG LIM]

Sorry, what are the template building code and template data file u mentioned above?

The first version is this?

While the second version is like this?

I couldn't see any differences between them? Thank you.

[Walter Roberson]

The posted template creation code does not build the .mat that is available there. The code to match input against the templates uses the templates that are actually present in the .mat.

The difference between the posted template creation code and the templates in the .mat file is that the real templates in the .mat file have an extra entry for each letter that has an interior "hole", such as "D" or "O".

[JIAHONG LIM]

Oh I got it. Thank you very much. Appreciate your explanation.