Why are you even using iamgesc() and then getframe() at all? There is no need. You can make the movie directly from your 3-D image without even displaying them at all if you don't want to. Just do something like this:
% Convert the 3-D array to a movie.
% Preallocate myMovie, which will be an array of structures.
% First get a cell array with all the frames.
[vidHeight, vidWidth, numberOfFrames] = size(handles.img);
allTheFrames = cell(numberOfFrames,1);
allTheFrames(:) = {zeros(vidHeight, vidWidth, 3, 'uint8')};
% Next get a cell array with all the colormaps.
allTheColorMaps = cell(numberOfFrames,1);
allTheColorMaps(:) = {zeros(256, 3)};
% Now combine these to make the array of structures.
myMovie = struct('cdata', allTheFrames, 'colormap', allTheColorMaps)
for frame = 1 : numberOfFrames
% Read the image in from disk.
thisFrame = handles.img(:,:, frame);
% Convert the image into a "movie frame" structure.
myMovie(frame) = im2frame(thisFrame);
% Write this frame out to a new video file.
writeVideo(writerObj, thisFrame);
end
close(writerObj);
