How to make a gif of an already animated figure

Hello,

I have been looking around for a bit but I cannot seem to find a solution which works for me.

So a colleague of mine send me a code which explains a proposal he made. This explaination is done by updating a figure using a loop, thus animating it. I would like to save this as animation as a .gif file, but I cannot get it to work. As soon as I open the file, I see the first frame and then the gif turns black.

So this is the code:

clear all
close all

C=imread('belletje.tif');
C=double(C);
%[x,y]=ndgrid(1:128);
%[X,Y]=ndgrid(28+(1:100));

% cut image to 100 by 100 pixels
Ctx=C(29:128,29:128);
clear x y X Y
Cmax=max(Ctx(:));
Cmin=min(log10(Ctx(:)/Cmax));
figure(1)
image(255*(1-log10(Ctx/Cmax)/Cmin))
axis equal
colormap bone(256)

% Ftx is the 2D Fourier transform of the original image Ctx
Ftx=fftshift(fft2(Ctx));
Fmax=max(20*log10(abs(Ftx(:)+1)));
Fscale=255/Fmax;
figure(2)
image(Fscale*20*log10(abs(Ftx+1)))
axis equal
colormap bone(256)

% Acc1-3 are the resulting (integrated) CCD images of the 3 succesive camera's 
Acc1=zeros(size(Ctx));
Acc2=zeros(size(Ctx));
Acc3=zeros(size(Ctx));

% per timestep Ftx shifts along the 3 camera postions with aperture stops
% in between. The sweep is performed from the bottom to the top.

for timestep=1:460 % in ns at 10 Mfps

      % LB is the total plane in front of the lens bank
      % 3 x (100x100) plus aperture stops of 3 x (20x100) 
      LB=zeros(360,100);
      % in principle 1 tot 100
      Start_Row_Index=1;
      End_Row_Index=100;
      % exception at begin and end
      if timestep < 100
          End_Row_Index=timestep;
      elseif timestep > 360
          Start_Row_Index=timestep-359;
      end
      % let Ftx shift over the entrance of the lens bank
      Row_Index=Start_Row_Index:End_Row_Index;
      LB(360-timestep+Row_Index,:)=Ftx(Row_Index,:);
      % devide LB over 3 camera channels
      N1=LB(241:340,:);
      N2=LB(121:220,:);
      N3=LB(1:100,:);
      % get image from each Fourier transform
      B_blind=zeros(20,100);  % the aperture stop
      B1=abs(ifft2(N1));
      B2=abs(ifft2(N2));
      B3=abs(ifft2(N3));
      % assemble the total image at the image plane (the CCD camera's)
      B=cat(1,B3,B_blind,B2,B_blind,B1, B_blind);
      % determine the integrated image on the CCD's per frame
      Acc1=Acc1+B1/100;
      Acc2=Acc2+B2/100;
      Acc3=Acc3+B3/100;
      % image on the CCD's 
      Acc=cat(1,Acc3,B_blind,Acc2,B_blind,Acc1,B_blind);

      figure(3)
      % plot
      % left row:     sweep of the Fourier transform
      % middle row:   resulting image on the plane of the CCD camera's
      % right row:    integrated pixel values on the CCD's
      subplot(1,3,1)
      image(Fscale*20*log10(abs(LB)+1))
      axis equal
      axis([0 100 0 360])
      subplot(1,3,2)
      image(B)
      axis equal
      axis([0 100 0 360])
      subplot(1,3,3)
      image(Acc)
      axis equal
      axis([0 100 0 360])
      colormap bone(256)
      drawnow
      pause(.1)

end

% normalization of the images in column 3
subplot(1,3,3)
AccMax=max(Acc(:));
AccMin=min(Acc(:));
image(255*(Acc/AccMax))
axis equal
axis([0 100 0 360])
colormap bone(256)

The code requires the following image

I tried adding

        f = getframe(figure(3));
        [im,map] = rgb2ind(f.cdata,256,'nodither');;
        im(:,:,1,timestep) = rgb2ind(f.cdata,map,'nodither');

in the loop followed by

imwrite(im,map,'Fourier.gif','gif','LoopCount',Inf,'DelayTime',1);

but this gave me the one-frame followed by black gif

I want the gif to be an animated image of the full figure with timestep (from 1 to 460).

Could anyone help me to a solution?

Thanks, Maarten

Answer 1

[Mike Garrity]

You also need WriteMode=append or the imwrite keeps creating a new file.

See the example at the end of this blog post .

[Adam Danz]

Starting in Matlab R2022a, another option is to use exportgraphics with append=true. See this Community Highlight for an example.