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how to construct a sequence from a folder of images

Asked by Elysi Cochin on 17 Nov 2012

i have a folder of images(say 20 images)... is it possible to construct a sequence from these images.... like a video or something like a slide show or something in such a way that it looks continuous....please do reply....

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Elysi Cochin

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1 Answer

Answer by Image Analyst on 17 Nov 2012
Edited by Image Analyst on 17 Nov 2012
Accepted answer

Refer to the FAQ: http://matlab.wikia.com/wiki/FAQ#How_can_I_create_a_movie_from_my_MATLAB_figures.3F

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

See the latter part of this demo where I read the images back in from disk and create an avi movie from them.

% Demo macro to extract frames and get frame means from an avi movie
% and save individual frames to separate image files.
% Also computes the mean gray value of the color channels.
clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
imtool close all;  % Close all imtool figures.
clear;  % Erase all existing variables.
workspace;  % Make sure the workspace panel is showing.
fontSize = 14;
% Change the current folder to the folder of this m-file.
% (The line of code below is from Brett Shoelson of The Mathworks.)
if(~isdeployed)
	cd(fileparts(which(mfilename)));
end
% Open the rhino.avi demo movie that ships with MATLAB.
folder = fullfile(matlabroot, '\toolbox\images\imdemos');
movieFullFileName = fullfile(folder, 'rhinos.avi');
% Check to see that it exists.
if ~exist(movieFullFileName, 'file')
	strErrorMessage = sprintf('File not found:\n%s\nYou can choose a new one, or cancel', movieFullFileName);
	response = questdlg(strErrorMessage, 'File not found', 'OK - choose a new movie.', 'Cancel', 'OK - choose a new movie.');
	if strcmpi(response, 'OK - choose a new movie.')
		[baseFileName, folderName, FilterIndex] = uigetfile('*.avi');
		if ~isequal(baseFileName, 0)
			movieFullFileName = fullfile(folderName, baseFileName);
		else
			return;
		end
	else
		return;
	end
end
try
	movieInfo = aviinfo(movieFullFileName)
	mov = aviread(movieFullFileName);
	% movie(mov);
	% Determine how many frames there are.
	numberOfFrames = size(mov, 2);
	numberOfFramesWritten = 0;
	% Prepare a figure to show the images in the upper half of the screen.
	figure;
	screenSize = get(0, 'ScreenSize');
	newWindowPosition = [1 screenSize(4)/2 - 70 screenSize(3) screenSize(4)/2];
	set(gcf, 'Position', newWindowPosition); % Maximize figure.
% 	set(gcf, 'Position', get(0,'Screensize')); % Maximize figure.
	
    % Ask user if they want to write the individual frames out to disk.
    promptMessage = sprintf('Do you want to save the individual frames out to individual disk files?');
    button = questdlg(promptMessage, 'Save individual frames?', 'Yes', 'No', 'Yes');
    if strcmp(button, 'Yes')
        writeToDisk = true;
          % Extract out the various parts of the filename.
          [folder, baseFileName, extentions] = fileparts(movieFullFileName);
          % 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
      else
          writeToDisk = false;        
      end
      % Loop through the movie, writing all frames out.
  	% Each frame will be in a separate file with unique name.
  	meanGrayLevels = zeros(numberOfFrames, 1);
  	meanRedLevels = zeros(numberOfFrames, 1);
  	meanGreenLevels = zeros(numberOfFrames, 1);
  	meanBlueLevels = zeros(numberOfFrames, 1);
      for frame = 1 : numberOfFrames
  		% Extract the frame from the movie structure.
  		thisFrame = mov(frame).cdata;
  		
          % Display it
          hImage = subplot(1,2,1);
          image(thisFrame);
          axis square;
          caption = sprintf('Frame %4d of %d.', frame, numberOfFrames);
          title(caption, 'FontSize', fontSize);
          drawnow; % Force it to refresh the window.		
		% Write the image array to the output file, if requested.
        if writeToDisk
             % Construct an output image file name.
            outputBaseFileName = sprintf('Frame %4.4d.png', frame);
            outputFullFileName = fullfile(outputFolder, outputBaseFileName);
              % Stamp the name and frame number onto the image.
              % At this point it's just going into the overlay, 
              % not actually getting written into the pixel values.
              text(5, 15, outputBaseFileName, 'FontSize', 20);
              % 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');
          end
		% Calculate the mean gray level.
		grayImage = rgb2gray(thisFrame);
		meanGrayLevels(frame) = mean(grayImage(:));
		% Calculate the mean R, G, and B levels.
		meanRedLevels(frame) = mean(mean(thisFrame(:, :, 1)));
		meanGreenLevels(frame) = mean(mean(thisFrame(:, :, 2)));
		meanBlueLevels(frame) = mean(mean(thisFrame(:, :, 3)));
		% Plot the mean gray levels.
		hPlot = subplot(1,2,2);
        hold off;
		plot(meanGrayLevels, 'k-', 'LineWidth', 2);
        hold on;
        plot(meanRedLevels, 'r-');
        plot(meanGreenLevels, 'g-');
        plot(meanBlueLevels, 'b-');
          % Put title back because plot() erases the existing title.
  		title('Mean Gray Levels', 'FontSize', fontSize);
          if frame == 1
  			xlabel('Frame Number');
  			yLabel('Gray Level');
              % Get size data later for preallocation if we read
              % the movie back in from disk.
              [rows columns numberOfColorChannels] = size(thisFrame);
          end
          % Update user with the progress.  Display in the command window.
          if writeToDisk
      		progressIndication = sprintf('Wrote frame %4d of %d.', frame, numberOfFrames);
          else
      		progressIndication = sprintf('Processed frame %4d of %d.', frame, numberOfFrames);
          end
  		disp(progressIndication);
  		% Increment frame count (should eventually = numberOfFrames
  		% unless an error happens).
  		numberOfFramesWritten = numberOfFramesWritten + 1;
      end
      % Alert user that we're done.
      if writeToDisk
          finishedMessage = sprintf('Done!  It wrote %d frames to folder\n"%s"', numberOfFramesWritten, outputFolder);
      else
          finishedMessage = sprintf('Done!  It processed %d frames of\n"%s"', numberOfFramesWritten, movieFullFileName);
      end
      disp(finishedMessage); % Write to command window.
      uiwait(msgbox(finishedMessage)); % Also pop up a message box.
      % Exit if they didn't write any individual frames out to disk.
      if ~writeToDisk
          return;
      end
      % Ask user if they want to read the individual frames from the disk,
      % that they just wrote out, back into a movie and display it.
      promptMessage = sprintf('Do you want to recall the individual frames\nback from disk into a movie?\n(This will take several seconds.)');
      button = questdlg(promptMessage, 'Recall Movie?', 'Yes', 'No', 'Yes');
      if strcmp(button, 'No')
          return;
      end
      % Read the frames back in, and convert them to a movie.
      % I don't know of any way to preallocate recalledMovie.
      for frame = 1 : numberOfFrames
          % Construct an output image file name.
          outputBaseFileName = sprintf('Frame %4.4d.png', frame);
          outputFullFileName = fullfile(outputFolder, outputBaseFileName);
          % Read the image in from disk.
          thisFrame = imread(outputFullFileName);
          % Convert the image into a "movie frame" structure.
          recalledMovie(frame) = im2frame(thisFrame);
      end
      % Get rid of old image and plot.
      delete(hImage);
      delete(hPlot);
      % Create new axes for our movie.
      subPlot(1, 3, 2);
      axis off;  % Turn off axes numbers.
      title('Movie recalled from disk', 'FontSize', fontSize);
      % Play the movie in the axes.
      movie(recalledMovie);
      % Note: if you want to display graphics or text in the overlay
      % as the movie plays back then you need to do it like I did at first
      % (at the top of this file where you extract and imshow a frame at a time.)
      msgbox('Done with this demo!');
catch ME
	% Some error happened if you get here.
	stError = lasterror;
	strErrorMessage = sprintf('Error extracting movie frames from:\n\n%s\n\nError: %s\n\n)', movieFullFileName, stError.message);
	uiwait(msgbox(strErrorMessage));
end

4 Comments

Elysi Cochin on 17 Nov 2012

sir this is the error msgbox being displayed..

Error extracting movie frames from: track.avi

Error: Output argument "varargout" [and maybe other] not assigned during call to

"C:\ProgramFiles\MATLAB\R2009b\toolbox\matlab\general\desktop.m>desktop"

sir please reply how to rectify this error

Image Analyst on 17 Nov 2012

I ran that line and selected the standard MATLAB demo movie called traffic.avi, and it returned fine, so the uigetfile() is not the problem. But the movieFullFileName is really the base filename (no folder) so you need to make sure you construct the full file name. I used sprintf to do that (you didn't). I have no idea why desktop.m is being run (is that the name of your m-file) or why varargout is not assigned. Do you know how to use the debugger to step through your code and examine variables? If you did, this would be easy to solve by yourself.

Elysi Cochin on 17 Nov 2012

sir now i got it....thank u so much for ur help.... thank u so much.... it was my mistake in naming... thank u sir....

Image Analyst

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