How to read images sequentially from a folder?

sourcefolder = 'E:\images';

filepattern = fullfile(sourcefolder, '*.png');
outputfolder = 'E:\images2';


srcFiles = dir(filepattern);
numImages = length(srcFiles);
for k = 1 : numImages
        
    inputfilename = fullfile(sourcefolder, srcFiles(k).name);
    outputfilename = fullfile(outputfolder, sprintf('histo_%d.png',k));
    .....
    ....
    ....
end

My folder containing 1400 images. Whenever I am reading images using the above code and after performing any image processing its not happening sequentially. How can read images by one by one maintaing the sequence and can write to them by maintaining the same order.

[Chunru]

you need to sort the srcFiles first according to your need.

[Zara Khan]

how to do that

Answer 1

[Stephen23]

You can download the file NATSORTFILES by clicking the big blue download button here:

https://www.mathworks.com/matlabcentral/fileexchange/47434-natural-order-filename-sort

then unzip the file onto the MATLAB search path (e.g. into the current directory), and then use it like this:

srcFiles = dir(filepattern);
srcFiles = natsortfiles(srcFiles);

[Zara Khan]

It worked. Thanks

Answer 2

[Pooja Kumari]

Dear Zara Khan,

It is my understanding that you want to access the images present in the folder sequentially and after performing some operations, you want to store the output image in ‘output filename’.

But the issue you were facing is that when you are reading images using the provided code and after getting the input file name and performing some image processing, you were not getting the output sequentially is because the files stored in input file name is not sequential.

You can refer to the updated code given below:

sourcefolder = 'E:\images'; %path of your source folder 

filepattern = (fullfile(sourcefolder, '*.png'));
srcFiles = dir(filepattern);
numImages = length(srcFiles);

outputfolder = 'E:\images2';

for i= 1: numel(srcFiles)
    I =(imread(strcat(sourcefolder,'/',srcFiles(i).name)));
    outputfilename = fullfile(outputfolder, sprintf('histo_%d.png',i));
    .....
        ....
        ...
end

Please find attached a reference code for the above issue you were facing:

% I have 50 images named numerically '15_1_s', '15_2_s', ... '15_50_s' but
% the order in which these files are stored is shown in the image below: 

path = '/MATLAB Drive/CV_Assignment2/dd/dd';
folder = (path);
files = dir(fullfile(folder,'*.jpg'));
nfiles = length((files));
mkdir(['Outputfolder',sprintf('%d',outputfolder)]);  % similar to outputfolder.

for i= 1: numel(files)
    I =(imread(strcat(path,'/',files(i).name)));
    imwrite(imgx,strcat(path_output,'/',files(i).name));
    %output will be stored sequentially . 
end

For more information on how to sort files stored in a directory , you can refer to the below link:

https://in.mathworks.com/matlabcentral/answers/167001-how-to-sort-file-when-reading-them-with-dir

You can refer to this file, if you want to sort the input files naturally:

https://in.mathworks.com/matlabcentral/fileexchange/47434-natural-order-filename-sort?requestedDomain=

Sincerely,

Pooja Kumari

[Zara Khan]

Thank you madam for very nice explanation of my problem. Thanks once again for the response. I have used the natsortfiles in this case and its working well till now. I will also give a try of your answer also. Thanks.

Answer 3

[Chunru]

% create some files
system('touch a.png');
system('touch c.txt');
pause(1)  % make sure b is newer in datenum
system('touch b.txt');

pause(.5)
% get the files
f = dir('*.*');
{f.name}

ans = 1×5 cell array
    {'.'}    {'..'}    {'a.png'}    {'b.txt'}    {'c.txt'}

% sort according to name
[~, idx] = sort({f.name})

idx = 1×5

1 2 3 4 5

fname = {f(idx).name}

fname = 1×5 cell array
    {'.'}    {'..'}    {'a.png'}    {'b.txt'}    {'c.txt'}

% sort according to datetime
[~, idx] = sort([f.datenum])

idx = 1×5

2 3 5 1 4

fname = {f(idx).name}

fname = 1×5 cell array
    {'..'}    {'a.png'}    {'c.txt'}    {'.'}    {'b.txt'}

[Zara Khan]

will this work for .png images ? As you are only creating text files?

[Chunru]

This works for any file. You can sort according to file name, size, created data, and so on.

[Zara Khan]

My images are already sorted. but after image processing whenever I am storing those images that is not happening in order. Then how I will be sure that reading of images are happening in order? As they are not in order so comparisons of images becoming difficult. I am using loop to read images.

[Chunru]

What do you mean "your images are already sorted"? How do you compare your images? Give some examples.

[Zara Khan]

Sorted by names . Like they are img1, img2,......img1400. I have tried with natsortfiles also. But the function is telling undefined

[Walter Roberson]

You need to use the Add-On Explorer to install natsortfiles .