MATLAB: Reading sequence of JPEG images from current directory

Question

Hi,

I want to read JPEG images from current directory. Images are named sequentially like image000, image001 and so on. I gave it a try and ended up with following working code:

clc; clear;
str = '1820'; filename = 'image1820';
X11 = zeros(27648,150);
for i = 1:150
    % read, convert to grayscale and resize the image
    jpegimg = imread(filename,'jpeg');
    img2d = rgb2gray(jpegimg); img2d = imresize(img2d,[144 192]);
    % store image in an array
    X11(:,i) = img2d(:);
    % update string 'str'
    str = str2double(str) + 1; str = num2str(str);
    noofzeros = 4 - length(str); zerostr = '';
    for j = 1:noofzeros
        zerostr = strcat(zerostr,'0');
    end
    str = strcat(zerostr,str);
    % update filename to be the next file in the folder
    filename = strcat('image',str);
end

But this code look very crude. I believe there is more elegant and perhaps faster way of doing this. Can you please tell me that 'more elegant and faster' way?

I could have done this in the following way, but 'dir' doesn't seem to work with JPEG images:

fileFolder = fullfile('D:','My Documents');
dirOutput = dir(fullfile(fileFolder,'image*','jpeg'));
fileNames = {dirOutput.name}';
numFrames = numel(fileNames);
I = imread(fileNames{1});
% Preallocate the array
sequence = zeros([size(I) numFrames],class(I));
sequence(:,:,1) = I;
% Create image sequence array
for p = 2:numFrames
    sequence(:,:,p) = imread(fileNames{p}); 
end

I get the following error when i run this code:

??? Index exceeds matrix dimensions.
Error in ==> image_to_vector at 18
I = imread(fileNames{1});
>>

which is due to the fact that 'dirOutput' is an empty structure:

>> dirOutput
dirOutput = 
0x1 struct array with fields:
    name
    date
    bytes
    isdir
    datenum
>>

Thanks!

Answer 1

http://matlab.wikia.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F

Together with:

filename = sprintf('image%03d.jpeg', K);