Using images in a for loop

I've split a video into frames and written them to my disk individually. Now I need to find the difference between 2 consecutive frames. How do I call those images in he loop? The images are saved as Frame 0001.png, Frame 0002.png....etc

Answer 1

[Walter Roberson]

http://matlab.wikia.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F

Answer 2

[Image Analyst]

I do that in my demo. Though I do the differencing as the frames are read in. In the latter half of the demo, after I've written out individual frames to individual files, I read in individual frames back in. You could of course switch the subtraction step to there if you want. See attachment (below in blue text).

[Sneheet]

Image Analyst, I'm sorry, I'm quite new to matlab and image processing. Where exactly in your code are you finding the difference between frames?

See, I want to discard the frames which do not contain motion, so I find the frame differences. Is it possible to write those frames which contain motion into an array and then convert them into a new single video?

[Walter Roberson]

I would imagine that he does the differencing somewhere near the comment line,

% Now let's do the differencing

[Sneheet]

OK,fine. Now if I want to save certain frames to another location, how do I do that?

[Shivaputra Narke]

Go to matlab help and search for imwrite. If you are new to Matlab you can use Matlab help.

[Image Analyst]

It's right there in the code. Take another look:

% Construct an output image file name.
outputBaseFileName = sprintf('Frame %4.4d.png', frame);
outputFullFileName = fullfile(outputFolder, outputBaseFileName);
% Extract the image with the text "burned into" it.
frameWithText = getframe(gca);
% frameWithText.cdata is the image with the text
% actually written into the pixel values.
% Write it out to disk.
imwrite(frameWithText.cdata, outputFullFileName, 'png');

You can make outputFolder whatever you want. For example I did this:

% Make up a special new output subfolder for all the separate
% movie frames that we're going to extract and save to disk.
% (Don't worry - windows can handle forward slashes in the folder name.)
folder = pwd;   % Make it a subfolder of the folder where this m-file lives.
outputFolder = sprintf('%s/Movie Frames from %s', folder, baseFileName);
% Create the folder if it doesn't exist already.
if ~exist(outputFolder, 'dir')
  mkdir(outputFolder);
end

But you could just replace that with your own folder:

outputFolder = 'd:\Narke\Images'; % Or whatever.
% Create the folder if it doesn't exist already.
if ~exist(outputFolder, 'dir')
    mkdir(outputFolder);
end

If it's just certain frames, you can set outputFolder on a frame by frame basis inside the loop if you wanted to vary it by frame number or some other condition/criteria.