How to store multiple image vectors into matrix rows?

Hi all, I have a folder which contains 200 BMP images, I am reading all the images, converting each image into a vector and then trying to store these image vectors into a matrix. Following is the code which is self-explanatory, though it looks quite right however when i run the script it give me the following error. Subscripted assignment dimension mismatch. Error in Readallimages (line 16) immat(437580,k)=imtovector myFolder = 'C:\Users\Sana\Desktop\DermoscopyImages'; if ~isdir(myFolder) errorMessage = sprintf('Error: The following folder does not exist:\n%s', myFolder); uiwait(warndlg(errorMessage)); return; end filePattern = fullfile(myFolder, '*.bmp'); bmpFiles = dir(filePattern); immat=zeros(437580,200); for k = 1:length(bmpFiles) baseFileName = bmpFiles(k).name; fullFileName = fullfile(myFolder, baseFileName); fprintf(1, 'Now reading %s\n', fullFileName); imageArray = rgb2gray(imread(fullFileName)); %Read image and convert to Gray imtovector=double(imageArray(:)); %convert 2D image into 1D vector immat(437580,k)=imtovector %Store image vectors into matrix imshow(imageArray); % Display image. drawnow; % Force display to update immediately. end Any sort of help in this regard would be highly appreciated. Thanks in advance