MATLAB: Getting error: “Movie cdata must be of type uint8 array” despite the fact that the movie cdata *is* of type uint8 array.

errormovieuint8

Hi! I'm trying to play a movie from an array of frames that I recorded using surf. Here is the code that is generating an error:
zlim manual;
frames(numel(T)) = struct('cdata',[],'colormap',[]);
for frame_num = 1:numel(T)
    surf(reshape(KE(frame_num, 2:m-1, 2:n-1), m-2, n-2));
    hold on
    surf(reshape(NE(frame_num, 2:m-1, 2:n-1), m-2, n-2));
    hold off
    zlim([0 140]);
    frames(frame_num) = getframe();
end
for frame_num = 1:numel(T)
    frames(frame_num).cdata = uint8(frames(frame_num).cdata);
end
movie(frames, 5)
and here is the error:
Error using hgMovie
Movie cdata must be of type uint8 array
Error in movie (line 41)
        builtin('hgMovie',varargin{:});
Error in astro2d_main (line 110)
movie(frames, 5)
I'm quite confused because a) I'm explicitly casting the cdata to uint8 and b) MATLAB reports that the data is in fact in the correct format anyway:
frames(1)
ans = 
         cdata: [343x435x3 uint8]
      colormap: []
Any help solving this would be wonderful! Thanks.
ps: let me add that the individual frames are rendering just fine and calling
image(frames(1).cdata)
does exactly what I expect it to.

Best Answer

Double-check that ALL the data is uint8.
 isUint8 = arrayfun(@(x) isequal(class(x.cdata), 'uint8'), frames) % Not tested but should work
If any of the elements of isUint8 are false, check the corresponding frames. My suspicion is that you previously had data in frames and that the T you're using this time has fewer elements than the T you used the first time you created frames. That "leftover" data may be interfering. If the last several elements of isUint8 are false, this would support that guess.
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