i need to convert a folder of 200 .jpg images to .mat (to create 200 separate .mat files). i know there should be an easy matlab for loop to do this but I need help (newbie). thanks!

i need to convert a folder of 200 .jpg images to .mat (to create 200 separate .mat files). i know there should be an easy matlab for loop to do this but I need help (newbie). thanks!

[Rik]

What have you tried so far?

[Esther Mead]

sorry, put my response in wrong place..

my reply:

thanks for your reply. oh man i've tried to look around for an answer for about four or more hours. so far, i've tried opening the matlab image batch processor, importing all of my jpg files and tried to apply a function to them all.

im = imread(‘file_name.jpg’);

save(‘file_name.mat’, ‘im’);

where i replace the above with the actual name of the individual filename, e.g., '0000.jpg' and '0000.mat'...

but, it only worked for the first file. because i don't know how to write the function to find the name of the file and set it to the same name but just convert from jpg to mat. i hope i'm making sense. again i'm new. thanks again!

Answer 1

[Guillaume]

folder = 'C:\somewhere\somefolder';
filelist = dir(fullfile(folder, '*.jpg'));  %get list of all jpg files in the folder
matnames = regexprep({filelist.name}, '\.jpg$', '.mat');  %replace .jpg by .mat in all file names

for fileidx = 1:numel(filelist)
    img = imread(fullfile(folder, filelist(fileidx).name)); %read image
    save(matnames{fileidx}, img);  %save in respective mat file
end

As for saving in HDF5 format, it's unclear if you want one file per image or just one hdf5 file with a dataset per image. In any case, you wouldn't use save as you have written but h5create and h5write.

Answer 2

[Rik]

You're quite close. You were only missing the way to generate char arrays from a pattern. To do that you can use the sprintf function. You will find a small example below. If you don't understand the syntax I encourage you to read the documentation. Matlab has excelent documentation with many examples.

for n=1:200
    im = imread(sprintf('%04d.jpg',n));
    save(sprintf('%04d.mat',n),'im');
end

[Kurt]

This conversion does not create the .mat structure that I am looking for. For example, if I feed it a 1024x2048x3 jpg file, I get a .mat file with an img structure that is 1024x2048x3 of class uint8.

As an example, the topo60c .mat file has this structure:

Name          Size      Bytes    Class
description   1x1       342      string
topo60c       180x360   518400   double
topo60cR      1x1       128      map.rastereff.GeographicCellsReference

Answer 3

[Image Analyst]

See the FAQ for code samples.

[Esther Mead]

Thank you, but after several hours of trying to get this to work and trying to read from the linkgs to find other info, I'm still failing. Let me try to ask my question in a more simple way:

How, in matlab, can I read all .jpg images in a folder and save them as .mat files?

Again, this is all I know:

im = imread(‘file_name.jpg’);

save(‘file_name.mat’, ‘im’);

[Rik]

Did you try the code in my answer?

[Esther Mead]

Yes, of course. That's what I've been trying for several hours (and trying to apply various tweaks to it that I found from my reading)...still no success.

[Esther Mead]

I'm sure it's a simple solution. I'll just ask someone in my class tomorrow. I was just trying to fix it before then. Unless someone else can answer here. Thanks again!

[Esther Mead]

here is the link to how i entered the code in the imageBatchProcessor:

https://www.dropbox.com/s/2gsgm3ka2jrmrxr/entered%20code%20in%20imageBatchProcessor.png?dl=0

and here is the link to the error i'm gettting:

https://www.dropbox.com/s/3gsqwesymyz1fm2/error.png?dl=0

[Esther Mead]

what i want to do is this, but for 210 images:

im = imread('00000000.jpg');

save('00000000.mat','im');

and then

im = imread('00000000.jpg');

save('00000000.h5','im');

so, for each of my 210 images, i want it in .jpg, .mat., and .h5

[Rik]

Apparently the file 00000001.jpg doesn't exist, so the underlying assumption of my code isn't true. You don't need the batch processor.

Did you make sure the current folder contains the files? Otherwise you will need to put the full path in your loader.

Also, the save function does not support saving a h5 file.

[Image Analyst]

Use the other FAQ code -- the one that uses dir() to get the filenames.