Hi everyone! How can I extract frames of a video in matlab if I have used mmreader to read the video.I have used frame2im command but its not working.
MATLAB: How to extract frames of a video
MATLABvideo
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Your code does not write anything to disk, other creating the folder. You display the frames but you do not imwrite() them to disk.
Try this demo. That is one of the things it does:
% 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; endendtry 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, 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
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