MATLAB: Trying to change name of image file in for loop – use %s

imagepsychtoolbox

Hi,

I'm trying to create a for loop, where I gather screen shots and save them (trial 1, trial 2…, etc.). I tried to use the following:

    imwrite(imageArray, '%s.jpg',trial)

to create different names for each image, as the loop continues. However, this didn't work. Is there any other way to do this, other than "if trial 1….else if trial 2, etc.?"

I am using PTB, if that's useful.

Thank you!

Best Answer

Use the filename as the following

for ii = 1:10
   filename = ['trial' num2str(ii) '.jpg']
   imwrite(I,filename)
end

It looks like what you were trying to do was use sprintf inside of imwrite. This would work too, but it a little more power than you need:

filename = sprintf('trial%i.jpg',ii)

Related Solutions

MATLAB: Save figure as image to folder with continuous numbering

All of this gets easier if you can set up conditions first and then loop doing the getframe and writing files sequentially, instead of each time having to independently figure out which file to write.

But to handle your situation as-is, and presuming that there are no other jpg files in the directory:

img = getframe(gcf);
nowstr = datestr(now, 'yyyymmddHHMM');
folder = 'C:\Users\Taiko\Desktop\FalseColor\';
ImageFiles = dir( fullfile(folder, '*.jpg') );
if isempty(ImageFiles)
   next_idx = 1;
else
  lastfile = ImageFiles(end).name;
  [~, basename, ~] = fileparts(lastfile);
  file_number_str = regexp('(?<=.*_)\d+$', basename, 'match' );
  if isempty(file_number_str)
     error('There is a .jpg file present that does not follow the expected naming pattern: "%s", lastfile);
  end
  last_idx = str2double(file_number_str);
  next_idx = last_idx + 1;
end
newfilename = fullfile( folder, sprintf('%s_%04d.jpg', nowstr, next_idx) );
imwrite(img.cdata, newfilename);

Note: if you expect to write more than 9999 frames in one series, then change the %04d to %05d or larger. Make sure that you keep the 0 after the % though. Not %4d for example.

Most this code could be eliminated if it was permitted to initialize some variables first and then write files in a loop instead of having to figure out what the next file is independently each time.

MATLAB: Problem in writing files

The problem is likely caused by the fact that your images are actually written to a different directory than you think.

I strongly recommend using fullfile rather than trying to concatenate paths and filenames.

Start with something like this:

D = 'E:\phd\zahra taati\extract only heart\crop100-112\';
S = dir(fullfile(D,'*.jpg'));
for k = 1:numel(S)
    F = fullfile(D,S(k).name);
    I = imread(F);
    J = ... do whatever you want with image I
    G = fullfile(D,['cropped',S(k).name]); % you forgot the path here!
    imwrite(J,G);
end

If you want to change the file extension then use fileparts to get the filename, then simply append the desired extension to the name.

Best Answer

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MATLAB: Save figure as image to folder with continuous numbering

MATLAB: Problem in writing files

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