read 20 images in ordered manner

Hi everybody. I have 20 images named 1.png,2.png,...,20.png

I want to read them in ordered manner and save them in a matrix called pic_3D. I wrote this code:

surf_read_dir='E:\phd\zahra taati\extract only heart\h70%\';
files=dir('E:\phd\zahra taati\extract only heart\h70%\*.jpg');
for im=1:size(files)
	fdir = strcat(surf_read_dir , files(im).name);
	slice_im = load(fdir);
	pic = imread(fdir);
	for i=1:500
		frt_data(im,:,i)=pic(i,:,1);
	end
	pic_3D(:,:,im) = pic(:,:,1);
end
end

but it doesn't read them from 1 to 20 in order and it reads them randomly. For example it saves 20.png before 5.png.

How should I correct my code?

Answer 1

[Walter Roberson]

See the File Exchange contribution https://www.mathworks.com/matlabcentral/fileexchange/47434-natural-order-filename-sort

Or, in your case because you know the file names are sequential, you could skip the dir() step and use

for im = 1 : 20
    fdir = fullfile(surf_read_dir, sprintf('%d.png'));
    pic = imread(fdir);
    frt_data(im, :, :) = pic(1:500,:,1);
    pic_3D(:,:,im) = pic(:,,:,1);
end

I would suggest, though, that instead of constructing frd_data at that point, that instead you construct just pic_3D in the loop, and then after the loop,

frt_data = permute( pic_3D(1:500,:,:), [2 3 1]);

Answer 2

[Image Analyst]

Part of the problem was in using a file pattern of *.jpg when you actually have *.png files. But also other errors. Try this (untested):

surf_read_dir='E:\phd\zahra taati\extract only heart\h70%\';
filePattern = fullfile(surf_read_dir, '*.png');
files = dir(filePattern)
for k = 1 : length(files) % May be 20 or whatever - this makes it not matter - it will do them all.
	baseFileName = sprintf('%k.PNG', k);
	fullFileName = fullfile(files(k).folder , baseFileName);
	if ~isfile(fullFileName)
		fprintf('%s not found.  Skipping slice %d.\n', fullFileName, k);
		continue;
	end
	thisSlice = imread(fullFileName);
	[rows, columns, numberOfColorChannels] = size(thisSlice);
	if numberOfColorChannels > 1
		thisSlice = thisSlice(:, :, 1); % Take red channel.
	end
	if k == 1
		frt_data = zeros(rows, columns, length(files), 'uint8');
	end
	frt_data(:,:, k) = thisSlice;
	fprintf('Inserting slice %d (%s) into 3-D array.\n', k, baseFileName);
end
pic_3D = frt_data; % Another variable with the same name for some reason.