How can I process multiple image with for loop?

Hi,

I know that this question was still asked but I didn't find my answer. I want to process multiple images with a for loop when images are open.

What I did:

      img1=imread('30.jpg');
      img2=imread('25.jpg');
      img3=imread('20.jpg');

      for i=1:3

          imagename=strcat('img',num2str(i))
          figure;
          imshow(imagename);

      end

I check and imagename return img1, img2 and img3. But imshow function can't work with these names and an error occured. Matlab return me:

??? Error using ==> getImageFromFile at 14
Cannot find the specified file: "img1"

Error in ==> imageDisplayParseInputs at 74
    [common_args.CData,common_args.Map] = ...

Error in ==> imshow at 199
  [common_args,specific_args] = ...

Error in ==> test at 13
    imshow(imagename);

I don't understand why have I an error because that they can't find "img1".

If somebody can help me, it will be very nice.

Thank you,

Yoann

Answer 1

[David Young]

You are passing a string to imshow, which it interprets as a filename. However, there isn't a file called "img1". If you wish to read all the images into main memory (MATLAB workspace) and then process them, it's best to use a cell array, like this:

      img{1}=imread('30.jpg');
      img{2}=imread('25.jpg');
      img{3}=imread('20.jpg');

      for i=1:3
          figure;
          imshow(img{i});
      end

Alternatively you can store the file names as a cell array of strings and read them in one at a time, just before displaying them:

      imfile{1}='30.jpg';
      imfile{2}='25.jpg';
      imfile{3}='20.jpg';

      for i=1:3
          img = imread(imfile{i});
          % process img here if you wish
          figure;
          imshow(img);
      end

I recommend revising MATLAB strings and array types - the introductory documentation is very helpful.