FANDOM



Demo macro to extract frames and get frame means from an avi movie and save individual frames to separate image files.Then rebuilds a new movie by recalling the saved images from disk.  Also computes the mean gray value of the color channels and detects the difference between a frame and the previous frame.

% Demo macro to extract frames and get frame means from an avi movie
% and save individual frames to separate image files.
% Then rebuilds a new movie by recalling the saved images from disk.
% Also computes the mean gray value of the color channels
% And detects the difference between a frame and the previous frame.
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
    videoObject = VideoReader(movieFullFileName)
    % Determine how many frames there are.
    numberOfFrames = videoObject.NumberOfFrames;
    vidHeight = videoObject.Height;
    vidWidth = videoObject.Width;
   
    numberOfFramesWritten = 0;
    % Prepare a figure to show the images in the upper half of the screen.
    figure;
    %     screenSize = get(0, 'ScreenSize');
    % Enlarge figure to full screen.
    set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
   
    % 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 = read(videoObject, frame);
       
        % Display it
        hImage = subplot(2, 2, 1);
        image(thisFrame);
        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(2, 2, 2);
        hold off;
        plot(meanGrayLevels, 'k-', 'LineWidth', 2);
        hold on;
        plot(meanRedLevels, 'r-');
        plot(meanGreenLevels, 'g-');
        plot(meanBlueLevels, 'b-');
        grid on;
       
        % 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;
       
        % Now let's do the differencing
        alpha = 0.5;
        if frame == 1
            Background = thisFrame;
        else
            % Change background slightly at each frame
            %             Background(t+1)=(1-alpha)*I+alpha*Background
            Background = (1-alpha)* thisFrame + alpha * Background;
        end
        % Display the changing/adapting background.
        subplot(2, 2, 3);
        imshow(Background);
        title('Adaptive Background', 'FontSize', fontSize);
        % Calculate a difference between this frame and the background.
        differenceImage = thisFrame - uint8(Background);
        % Threshold with Otsu method.
        grayImage = rgb2gray(differenceImage); % Convert to gray level
        thresholdLevel = graythresh(grayImage); % Get threshold.
        binaryImage = im2bw( grayImage, thresholdLevel); % Do the binarization
        % Plot the binary image.
        subplot(2, 2, 4);
        imshow(binaryImage);
        title('Binarized Difference Image', 'FontSize', fontSize);
    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 from disk, and convert them to a movie.
    % Preallocate recalledMovie, which will be an array of structures.
    % First get a cell array with all the frames.
    allTheFrames = cell(numberOfFrames,1);
    allTheFrames(:) = {zeros(vidHeight, vidWidth, 3, 'uint8')};
    % Next get a cell array with all the colormaps.
    allTheColorMaps = cell(numberOfFrames,1);
    allTheColorMaps(:) = {zeros(256, 3)};
    % Now combine these to make the array of structures.
    recalledMovie = struct('cdata', allTheFrames, 'colormap', allTheColorMaps)
    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.
    strErrorMessage = sprintf('Error extracting movie frames from:\n\n%s\n\nError: %s\n\n)', movieFullFileName, ME.message);
    uiwait(msgbox(strErrorMessage));
end

Ad blocker interference detected!


Wikia is a free-to-use site that makes money from advertising. We have a modified experience for viewers using ad blockers

Wikia is not accessible if you’ve made further modifications. Remove the custom ad blocker rule(s) and the page will load as expected.