Try this demo. It does that.
% 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
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.
stError = lasterror;
strErrorMessage = sprintf('Error extracting movie frames from:\n\n%s\n\nError: %s\n\n)', movieFullFileName, stError.message);
uiwait(msgbox(strErrorMessage));
end
