How can I fill an array of images from inside a for loop?

Hi all.

I'm trying to read a bunch of images of faces from a directory within the current directory into an accessible array I can use later on to display one of them randomly.

Here's what I've got so far:

      FaceFolder = 'Faces';

if ~isdir(FaceFolder)
        errorMessage = sprintf('Error: The following folder does not exist:\n%s', FaceFolder);
        uiwait(warndlg(errorMessage));
        return;
end

      filePattern = fullfile(FaceFolder, '*.bmp');
      bitmapFiles = dir(filePattern);

      AllFaces=zeros(length(bitmapFiles), 638);

for k = 1:length(bitmapFiles)
    baseFileName = bitmapFiles(k).name;
    fullFileName = fullfile(FaceFolder, baseFileName);
    fprintf(1, 'Now reading %s\n', fullFileName);
    currentim = imread(fullFileName);
    AllFaces(k,:) = currentim;
end

I keep getting "Subscripted assignment dimension mismatch" errors for the AllFaces(k,:) = currentim; line.

638 is what I believe to be the size of one of the bitmap files (they're all the same dimensions) hence that number, so I tried using that to set up an array of zeros before the loop to fill it in but clearly I'm doing something wrong.

Anyone have any ideas?

Answer 1

[Evan]

It looks like you're trying to assign a [nxm] matrix (the image) to a [1xm] row in AllFaces. Instead, try this:

AllFaces(:,:,k) = currentim;

[Max]

Hmm I'm still returned with the same "Subscripted assignment dimension mismatch." error.

When I try:

length(currentim)

I'm returned with the value 638 which is where I got that number.

[Max]

I also tried:

size(currentim)

And was returned with 480, 638, 3.

So I tried:

AllFaces=zeros(length(bitmapFiles), 480, 638, 3);

for k = 1:length(bitmapFiles)
    baseFileName = bitmapFiles(k).name;
    fullFileName = fullfile(FaceFolder, baseFileName);
    fprintf(1, 'Now reading %s\n', fullFileName);
    currentim = imread(fullFileName);
    AllFaces(:,:,:,k) = currentim;
end

But still same error.

[Evan]

Oh, I didn't see above where you initialized "AllFaces" before your loop. That's the problem. Does changing that part to the below code work?

AllFaces = zeros(480,638,3,length(bitmapFiles))

[Max]

Ah, sorry I miscopied something.

Here's the most recent iteration that still returns the error:

      AllFaces=zeros(length(bitmapFiles), 480, 638, 3);

for k = 1:length(bitmapFiles)
    baseFileName = bitmapFiles(k).name;
    fullFileName = fullfile(FaceFolder, baseFileName);
    fprintf(1, 'Now reading %s\n', fullFileName);
    currentim = imread(fullFileName);
    AllFaces(k,:,:,:) = currentim;
end

The pre-allocated array's "length" column is aligned with the "k" column I'd like to fill which I think is right.