How can I fix graph title jittering in MATLAB movie.

I have been trying to make a movie using MATLAB out of graphs consisting of a a pcolor graph with a quiver plot overlayed on it. The problem I am having is that the graph title jumps up and down while the movie is being displayed. Fro example when the frame jumps from 11 to 12 the title goes downward. Is there a way to fix this problem.

      clear all;
      close all;

      writeMovie = true;

      if(writeMovie)
          vidObj = VideoWriter('testquiver.avi');
          vidObj.Quality = 25;
          vidObj.FrameRate = 10;
          open(vidObj);

      else
      end

      figure
      t = 0:0.1:4;
      [X,Y] = meshgrid(-10:.2:10,-2:.2:2);
      for ii = 1:length(t)
          Z = X.*exp(-X*sin(t(ii)).^2 - Y.^2);
          [DX,DY] = gradient(Z,.2,.2);

          subplot(2,1,1);
          pcolor(X,Y,Z)
          shading interp
          hold on
          quiver(X(2:2:end),Y(2:2:end),DX(2:2:end),DY(2:2:end),'LineWidth',1,'Color', 'k')
          colormap hsv
          hold off

          xlabel('some text');
          ylabel('some text');
          title(['some more text frame number = ', num2str(ii)]);
          axis image
          axis off

          subplot(2,1,2)
          pcolor(X,Y,Z*-1)
          [DX,DY] = gradient(Z*-1,.2,.2);
          shading interp
          hold on
          quiver(X(2:2:end),Y(2:2:end),DX(2:2:end),DY(2:2:end))
          colormap hsv
          hold off

          pause(0.1);

          if(writeMovie)
             currFrame = getframe(gcf);
             writeVideo(vidObj,currFrame);
          else
          end

      end

      % Create AVI file.
      if(writeMovie)
      close(vidObj);
      end

[Matt Fig]

Does this actually make a movie on your machine? On mine it plays a movie that consists only of one frame (the first one).

[Timothy]

Yes. It should play a movie with 41 total frames. I just copied and pasted the code above into MATLAB and it worked for me.

[Matt Fig]

Yes, I see the plot itself changing, but if I open the .avi file with my default movie player, it contains only one frame that keeps looping - no change.

Must be a bug on my machine or in MATLAB.

Answer 1

[Image Analyst]

I agree with Matt. The movie looks like garbage. Mine is some kind of blurred frame #1 blended with MATLAB code in the background and that frame never changes throughout the whole movie. Not sure why since it looks like you followed the directions in the help. Maybe you could use movie2avi instead.

Anyway, the title moving is due to the quiver arrows sticking out of the image. When they extend out past the colored part of your frame, the title moves up to maintain a constant distance between the title and the top-most part of the chart/image. I don't know how to fix. You might try playing with the 'Position' property of the image or quiver. And there are several flavors of position to look at, like 'outerposition', etc.

Alternatively you might want to look into avoiding pcolor (which I hate) at all. Try to do the same thing with image() or imshow().

Answer 2

[Matt Fig]

Try this out. It stops the jittering on my machine. Still don't know about the .avi file, but the plotting is steady. I only added a few lines of code to what you wrote.

clear all;
close all;

writeMovie = true;

if(writeMovie)
    vidObj = VideoWriter('testquiver.avi');
    vidObj.Quality = 25;
    vidObj.FrameRate = 10;
    open(vidObj);

else
end

figure('pos',[624   474   672   504])
t = 0:0.1:4;
[X,Y] = meshgrid(-10:.2:10,-2:.2:2);
for ii = 1:length(t)
    Z = X.*exp(-X*sin(t(ii)).^2 - Y.^2);
    [DX,DY] = gradient(Z,.2,.2);

      subplot(2,1,1);
      P = pcolor(X,Y,Z);
      shading interp
      hold on
      Q = quiver(X(2:2:end),Y(2:2:end),DX(2:2:end),DY(2:2:end),'LineWidth',1,'Color', 'k');
      colormap hsv
      %     hold off

      xlabel('some text');
      ylabel('some text');
      axis image
      axis off

      subplot(2,1,2)
      P(2) = pcolor(X,Y,Z*-1);
      [DX,DY] = gradient(Z*-1,.2,.2);
      shading interp
      hold on
      Q(2) = quiver(X(2:2:end),Y(2:2:end),DX(2:2:end),DY(2:2:end));
      colormap hsv
      axis off

      if ii==1
          T = text(-7,8,'temp','fontweight','bold','fontsize',14);
      end

      if ii<10
          STR = ['some more text frame number = 0', num2str(ii)];
      else
          STR = ['some more text frame number = ', num2str(ii)];
      end

      set(T,'string',STR)
      pause(0.1);

      if(writeMovie)
          currFrame = getframe(gcf);
          writeVideo(vidObj,currFrame);
      else
      end

      delete([P Q])

end

% Create AVI file.
if(writeMovie)
    close(vidObj);
end