How to solve error "Index exceeds the number of array elements (12)."?

Hi, My code is as follows:

% Specify the folder where the files live.
myFolder = 'location';

filePattern = fullfile(myFolder, '*.bmp'); 
theFiles = dir(filePattern);

 for k = 1 : length(theFiles)
    baseFileName = theFiles(k).name;
    
    fullFileName = fullfile(theFiles(k).folder, baseFileName);
    imageArray = imread(fullFileName);
    r=1;
    a=1;
    for q=0.1:0.01:0.5
    bw=im2bw(imageArray,q);
    
    
   %%
  % masked image is defined here 
   %%
   
   
blackpix=im2bw(maskedRgbImage,q);  
num(r)=sum(blackpix(:) == 0);  %calculating black pixels

if(q>0.1)
    if (num(r)/num(r-1)>8 &&a==1)   %there's always a spike of pixel increase between two certain values.
   thresh(k)=q;  % When spike occurs, we take the value
   a=2;  %making sure only the fisrt spike is taken
    end
end
    r=r+1

    end
    num=[];  %setting the array as null before entering into q with incremented k.
 end
 
%% Same code again for putting the q from previous segment
 
for k = 1 : length(theFiles)
    baseFileName = theFiles(k).name;
    fullFileName = fullfile(theFiles(k).folder, baseFileName);
    fprintf(1, 'Now reading %s\n', fullFileName);

    imageArray = imread(fullFileName);
 
     bw=im2bw(imageArray,thresh(k));
       imshow(bw)
end

But when I give a large number of inputs, (more than 12) then it shows the following error:

Index exceeds the number of array elements (12).

Error in Untitled13 (line 117)
     bw=im2bw(imageArray,thresh(k));

Can you guys tell me what I am missing here?

[Tawsif Mostafiz]

Thanks, I solved it!

Answer 1

[Walter Roberson]

if(q>0.1)
    if (num(r)/num(r-1)>8 &&a==1)   %there's always a spike of pixel increase between two certain values.
   thresh(k)=q;  % When spike occurs, we take the value
   a=2;  %making sure only the fisrt spike is taken
    end
end

You only set thresh(k) in that condition, which means that for some files you might never set it.

 for k = 1 : length(theFiles)

No file after the 12 file happened to set the corresponding thresh()

     for k = 1 : length(theFiles)
       %stuff
       bw=im2bw(imageArray,thresh(k));

You are unconditionally using thresh(k) even though you only assign to thresh(k) conditionally.

I suggest you initialize

       thresh = nan(1, length(theFiles));

and that will solve the problem of thresh sometimes not being initialized... and will change it into the problem of figuring out what it means to use NaN as the threshold for im2bw()