Convert color video to grayscale video in MATLAB

Question

I am trying to do some operations on color video in MATLAB however, I am facing 2 problems:

• I am getting an error while converting color video to grayscale

Answer 1

Your first problem is due to trying to assign the 2D output of rgb2gray into a 3D array. You can fix this by converting the gray image back to RGB format:

  frames(:,:,:,i)=repmat(rgb2gray(frames(:,:,:,i)),[1 1 3]);

Answer 2

%% convert a RGB video to a grayscale one.
videoFReader = vision.VideoFileReader('xylophone.mpg');
videoFWriter = vision.VideoFileWriter('xylophone_gray.avi',...
   'FrameRate',videoFReader.info.VideoFrameRate);
while ~isDone(videoFReader)
   videoFrame = step(videoFReader);
   step(videoFWriter, rgb2gray(videoFrame));
end
release(videoFReader);
release(videoFWriter);

Answer 3

Try it this way. This should do the trick. The code is self-explanatory.

 vid = VideoReader('xylophone.mpg');
 numImgs = get(vid, 'NumberOfFrames');
 frames = read(vid);
 obj=VideoWriter('somefile.avi');
 open(obj);

 for i=1:numImgs
     movie(i).cdata=rgb2gray(frames(:,:,:,i));
     movie(i).colormap=gray;
 end

 writeVideo(obj,movie);
 close(obj);