Creating Animated Gifs with Linux

• Animated Gifs with Matlab and Convert

  • Download the mpgwrite.tar archive from the mathworks user-contributed mfiles site.

  • Untar the archive with: tar xvf mpgwrite.tar

  • The precompiled mex functions will exist in the pub/contrib/v5/graphics/mpgwrite directory, while the source will exist in the pub/contrib/v5/graphics/mpgwrite/src directory.

  • Open up matlab and make sure you are in the mpgwrite directory (or that it is in your matlab path, which you can do with the addpath function in matlab).

  • Here is a quick sample movie you can make to test it out:

    figure(1);
    clf;
    set(1,'color','w'); hold on;
    axis([-1 1 -1 1]);
    axis image;
    axis off;
    
    numframes = 20;
    
    x = linspace(-1,1,20);
    y = linspace(-1,1,20);
    [x,y]=meshgrid(x,y);
    t = linspace(0,4*pi,numframes);
    
    M = moviein(numframes);
    for n=1:numframes,
    cla;
    z = sin(4*x-sin(t(n))).*cos(4*y-cos(t(n)));
    surf(x,y,z);
    shading interp;
    M(:,n) = getframe;
    pause(0);
    end
    movie(M);

  • Now that you have a matlab movie matrix, you can use the mpgwrite function to generate the mpg file. This is done with

    >> mpgwrite(M,colormap,'movie_file.mpg');

    If this does not work then you are using a version of Matlab that is too new for mpgwrite to work. Mpgwrite assumes the matrix M is 2-d, while newer versions of Matlab (5.3 or greater) have M as a struct array. You will have to write your m-file accordingly to account for this change.

  • This will create a .mpg file called movie_file.mpg in the current directory. Check to see if this worked with an mpeg player by typing

    >> !xanim movie_file.mpg

    Don't worry if the movie doesn't come out very well with xanim. Converting it to a gif will improve it.

  • Now that you have a .mpg file, you need to convert it to a gif by using the convert program from ImageMagick.
    convert should come standard with the mpeg libraries in the RedHat 6.0 distribution, but if you have an older version then you can download the mpeg libraries from mpeg's site here: mpeg2vidcodec_v12.tar.gz.

  • Once you have convert installed with the mpeg libararies, you can convert your mpg to a gif with

    >> !convert -crop 0x0 -geometry 25% -loopback 0 movie_file.mpg movie_file.gif

    with the following options supported by convert:

    • -crop 0x0 : removes any extraneous borders around the image.
    • -geometry 25% : reduces the size of the movie by 25%.
    • -loopback : sets the gif animation to loop around and repeat.

  • You should now have a gif file with looping capabilities that you can add to your web pages. The movie_file.gif is shown below and was created with the steps outlined above. For more information on how to place gifs on the web, click here
    

  Last Updated: 6/16/99