MATLAB: Unable to perform assignment because the indices on the left side are not compatible with the size of the right side.

image processing

Hi,
I am working on character recogntiion and my images are in gray images.
here in the code on read all images but I am facing error. 
function [images, labels, imageFiles] = readDataset(dirPath)
    imageFiles = '';
    % Get a list of all files and folders in this folder.
    files = dir(dirPath);
    % Get a logical vector that tells which is a directory.
    dirFlags = [files.isdir];
    % Extract only those that are directories.
    subFolders = files(dirFlags);
    % add all image file name
    for i = 1 : length(subFolders)
      subDir = subFolders(i).name;
      if subDir == '.' | strcmp(subDir, '..') == 1
          continue;
      end
      
      files = dir(strcat(dirPath, '/', subDir));
      fileFlags = ~[files.isdir];
      files = files(fileFlags);
      for j = 1: length(files)
          filename = strcat(subDir, '/', files(j).name);
          imageFiles = strvcat(imageFiles, filename);
      end
    end
    
    % shuffle file list
    idx = randperm(length(imageFiles));
    imageFiles = imageFiles(idx, :);
    
    % read images and labels
    images = [];
    labels = [];
    for j = 1: length(imageFiles)
      filenames = strsplit(imageFiles(j, :), '/');
      a = str2num(filenames{1});
      labels = [labels, str2num(filenames{1})];
      img = imread(strcat(dirPath, '/', imageFiles(j, :)));
      %img = rgb2gray(img);
      img = imresize(img, [32, 32]);
      img = double(img) / 255;
      images(:, :, length(labels)) = img;          
    end
    
    labels = reshape(labels, [length(labels), 1]);
    images = reshape(images, [32, 32, 1, length(labels)]);
end

Best Answer

Use the debugger to find the cause of the problem. Type e.g. this in the command window:
dbstop if error
Run the code again. When Matlab stops at the error, check the currently used variables:
size(img)
size(images)
Maybe the rgb2gray is important?
Some hints:
  • fullfile(a,b) is smarter than [a, '/', b], because it considers the fileseparators of the platform.
  • The names of the variables look confusing: "filenames" is not a list of file names, "a" is meaningless,
  • labels = reshape(labels, [length(labels), 1]) can be written as labels = labels(:).
  • The condition if subDir == '.' | strcmp(subDir, '..') == 1 can be simplified. Remember that == is the elementwise operation and subDir is a char vector. If subDir is '..', the comparison replied [true, true]. Because if requires a scalar condition, Matlab inserts an all implicitly. Then this is suffcient actually: if subDir == '.', because it catchs '..' also. Writing this explicitly is nicer to read: if all(subDir == '.'). This would trigger also for '...', but this is not an allowed file name under Windows, but maybe under Linux (?). Therefore I prefer the explicit: if strcmp(subDir, '.') || strcmp(subDir, '..')
Prefer to work with cell strings (or strings) instead of CHAR matrices. Replace:
imageFiles = '';
...
      files = dir(strcat(dirPath, '/', subDir));
      fileFlags = ~[files.isdir];
      files = files(fileFlags);
      for j = 1: length(files)
          filename = strcat(subDir, '/', files(j).name);
          imageFiles = strvcat(imageFiles, filename);
      end
by
      imageFiles = {};
      ...
      files      = dir(fullfile(dirPath, subDir));
      fileNames  = {files(~[files.isdir]).name};
      imageFiles = cat(2, imageFiles, fileNames);
      ...
      % Instead of imageFiles(j, :) use imageFiles{j} afterwards
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