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How to read images sequentially from a folder?

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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));
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.

Accepted Answer

Stephen23 on 5 Jul 2022
Edited: Stephen23 on 6 Jul 2022
You can download the file NATSORTFILES by clicking the big blue download button here:
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);

More Answers (2)

Pooja Kumari
Pooja Kumari on 5 Jul 2022
Edited: Pooja Kumari on 5 Jul 2022
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));
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)));
%output will be stored sequentially .
For more information on how to sort files stored in a directory , you can refer to the below link:
You can refer to this file, if you want to sort the input files naturally:
Pooja Kumari
  1 Comment
Zara Khan
Zara Khan on 6 Jul 2022
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.

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Chunru on 5 Jul 2022
Edited: Chunru on 5 Jul 2022
% create some files
system('touch a.png');
system('touch c.txt');
pause(1) % make sure b is newer in datenum
system('touch b.txt');
% get the files
f = dir('*.*');
ans = 1×5 cell array
{'.'} {'..'} {'a.png'} {'b.txt'} {'c.txt'}
% sort according to name
[~, idx] = sort({})
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
Zara Khan on 5 Jul 2022
Edited: Zara Khan on 5 Jul 2022
Sorted by names . Like they are img1, img2,......img1400. I have tried with natsortfiles also. But the function is telling undefined
Walter Roberson
Walter Roberson on 5 Jul 2022
You need to use the Add-On Explorer to install natsortfiles .

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