How to cut frames from video and then automatically crop the area of interest in all frames.

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Davit Hakobyan 2013-5-28

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https://ww2.mathworks.cn/matlabcentral/answers/77263-how-to-cut-frames-from-video-and-then-automatically-crop-the-area-of-interest-in-all-frames

采纳的回答： Image Analyst

eventually build 3D plot with this images, with third dimension as a time evolution of images.

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Image Analyst 2013-5-28

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https://ww2.mathworks.cn/matlabcentral/answers/77263-how-to-cut-frames-from-video-and-then-automatically-crop-the-area-of-interest-in-all-frames#answer_86917

What is a 3D plot? Did you try VideoReader to extract frames, and just imcrop or normal indexing to extract the ROI?

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Image Analyst 2013-5-31

在 MATLAB Online 中打开

OK, here - I've done what you described (almost). I take each frame, extract a column from the green channel, then take the mean intensity of that extracted column. I plot both the mean value, and the extracted lines themselves as a function of frame number. All that's left for you to do is to change the filename from rhinos.avi to whatever your video is called.

% Demo macro to extract frames and get frame means from an avi movie
% Also computes the mean gray value of a column of the green color channel.
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;
% 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]);
  
  % Loop through the movie, writing all frames out.
  % Each frame will be in a separate file with unique name.
  meanGrayLevels = zeros(numberOfFrames, 1);
  newVideoHeight =  min([799, vidHeight]) - 199;
  extractedImage = zeros(newVideoHeight, numberOfFrames, 'uint8');
  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.
    
    % Extract line 500 from the greenChannel
    % In essence crop this rectangle: [500 200 1 600]);
    row1 = 200;
    row2 = min([799, vidHeight]);
    columnToExtract = 500;
    if columnToExtract > vidWidth
      % Move to middle column if column is outside of image boundaries.
      columnToExtract = floor(vidWidth/2);
    end
    greenLine = thisFrame(row1:row2, columnToExtract, 2); % 2 means green
    
    % Store it in our new image we're building of the green lines.
    extractedImage(:, frame) = greenLine;
    subplot(2, 2, 3);
    cla;
    imshow(extractedImage);
    title('Column 500 of the Green Channel', 'FontSize', fontSize);
    xlabel('Frame Number');
    ylabel('Row Number');
    axis on;
    drawnow;
    
    % Calculate the mean gray level.
    meanGrayLevels(frame) = mean(greenLine(:));
    
    % Plot the mean gray levels.
    hPlot = subplot(2, 2, 2);
    hold off;
    plot(meanGrayLevels, 'k-', 'LineWidth', 2);
    grid on;
    
    % Put title back because plot() erases the existing title.
    caption = sprintf('Mean Gray Levels of column %d of the Green Channel.', columnToExtract);
    title(caption, '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.
    progressIndication = sprintf('Processed frame %4d of %d.', frame, numberOfFrames);
    disp(progressIndication);
    % Increment frame count (should eventually = numberOfFrames
    % unless an error happens).
    numberOfFramesWritten = numberOfFramesWritten + 1;
    
  end
  
  % Alert user that we're done.
  finishedMessage = sprintf('Done!  It processed %d frames of\n"%s"', numberOfFramesWritten, movieFullFileName);
  disp(finishedMessage); % Write to command window.
  uiwait(msgbox(finishedMessage)); % Also pop up a message box.
    
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

Image Analyst 2013-5-31

在 MATLAB Online 中打开

Yep, so you just did

greenLine = thisFrame(row1:row2, 490:510, 2);

and it all worked for you. Glad I could help. We're all done now, right?

Davit Hakobyan 2013-6-1

Yes I have wrote one bye myself and adjusted your demo, now I am done with this and have to codes. Now I need indexed color surfaces. Urgent I am on it, if you know how to find stuff like that tell me.

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