MATLAB: How to halt program until file input

halt programinput image

Hi, I am making an image processing program and want to know if there is a way to halt the program and make it wait for a image to be created before it is read. To put it into context,

imagefiles = dir('*.jpg');
nfiles = length(imagefiles);
for a = 1:200
    filename = ['image-' num2str(a,'%02d') '.jpg'];
    image = imread(filename);

I understand pause(n) might work but because the inputted images take different times to be snapped, I would like to make it dependent on when the file appears.

Any suggestions would be great!

Best Answer

You could put in a while loop checking whether the file exist().

count = 0;
while exist(filename)==0
 pause(1)
 count = count+1;
 if count ==10000
   disp('no file was generated in allowed time');
   break
end

I also put in a simple time out as well. I suggest you put in a

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your problem is you're trying to change the value of the loop index k inside the loop.

that doesn't do anything because matlab for loops don't work like a traditional for loop does (in C, C++, C#, Java, JS, whatever language you know), instead, it sets i to the next value in the loop vector each iteration (ehm foreach loop)

look here:

x = [];
for i = 1:10
    x = [x i];
    
    % try to skip number 6
    if i == 5
        i = 7;
    end
end
disp(x);

1     2     3     4     5     6     7     8     9    10

so instead of skiping i = 6 as expected, it simply ignores the fact that we changed i inside the loop and the output of this loop is the entire array.

The answer to your question is just use a while loop (there were a few other issues with your code, I cleaned it up a bit):

waitMax = 20;
k = 1;
while k < 6
    jpgFilename = sprintf('image%d.jpg', k);
    fullFileName = fullfile('C:\fproject\final_project\', jpgFilename);
    if exist(fullFileName, 'file') %if the image exist in the folder
        rgbImage = imread(fullFileName); 
        figure, imshow(rgbImage)
    else
        for count=1:waitMax
            %wait 20 seconds to the image 
            pause(1)
            if exist(fullFileName, 'file')
                k=k-1;
                break; %Exit this loop (return to the main loop)
            end
        end
    end
    k=k+1;
end

Best Answer

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