Reading sequence of JPEG images from current directory

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

[Walter Roberson]

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

Together with:

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

Answer 2

[Image Analyst]

Try 'image*.jpg' in your dir function. It's probably looking for files with no extension whatsoever so if your files have extensions, it won't retrieve those.

And I don't think either of those codes is particularly elegant or robust. Bad variable names, changing the class of str, not checking file sizes before concatenating, using weird string constructs instead of the simpler sprintf() like Walter suggested, not checking on dirOutput before proceeding, etc. However you did okay at adding comments, which most people don't.

[Ashish Bhatt]

After making the changes as below:

dirOutput = dir(fullfile(fileFolder,'image*.jpeg'));

i still get the same error. However, if I input a .gif file, program works fine:

dirOutput = dir(fullfile(fileFolder,'image*.gif'));

[Swapna Tekale]

I have the same problem for image sequence. It is working for *.tif file but not for .jpg. Please help me.

Answer 3

[Delowar Hossain]

You can try this code

srcFiles = dir('C:\Users\coil-20-proc\*.jpeg');  % the folder in which ur images exists
for i = 1 : length(srcFiles)
    filename = strcat('C:\Users\coil-20-proc\',srcFiles(i).name);
    I = imread(filename);
    figure, imshow(I);
end

[Walter Roberson]

fullfile is recommended instead of strcat() of the directory

[Nav Desh]

srcFiles take the images in a manner as image1,image10,image100 likewise.it does take the images in sequencelike image1,image2,image3.. how to change that sequence? Thanks in advance.

[Image Analyst]

Nav, see http://blogs.mathworks.com/pick/2014/12/05/natural-order-sorting/

http://blogs.mathworks.com/pick/2006/09/11/file1-file10-file2-sorting-problem-solved/