Why some of my colored videos load as gray-scale in MATLAB

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Mona 2016-5-16

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编辑： Mona 2016-6-6

Hi, I downloaded a bunch of videos from youtube. I then load them to matlab to extract/process 10 randomly selected clips. Most of my videos load perfectly fine, however, a lot of them load as a weird gray-scale version of the video. I load the videos using:

   vidObj     = VideoReader(filename);
   duration   = vidObj.Duration ;
   clips_indx = duration * rand(10,1);
   for i = 1 : 10
       vidObj.CurrentTime = clips_indx(i);
       im = readFrame(vidObj);
   end

This is how the clips look like, tilted and gray!

While the video looks normal like:

I would appreciate any input.

Thanks a lot.

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回答（2 个）

Walter Roberson 2016-5-16

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1) It is possible for videos to be pseudocolor; in such a case when you retrieve the frame, the map field will be non-empty and the data field will be 2D.

2) With a shear like that, it is plausible that the video is in YCrCb 4:2:2 or 4:2:0 and needs to be converted to RGB.

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Walter Roberson 2016-5-21

I don't know at the moment. Some technical notes on the codecs Youtube uses: http://video.stackexchange.com/questions/5318/how-does-youtube-encode-my-uploads-and-what-codec-should-i-use-to-upload

Mona 2016-5-21

Thanks a lot again. You've been so helpful.

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Mona 2016-6-6

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编辑：Mona 2016-6-6

在 MATLAB Online 中打开

Hi, I wasn't able to resolve this problem. However, I just had to find a way to go around it. So my very inefficient way is to : - Read the file using vision.VideoFileReader

vidObj = vision.VideoFileReader(filename);

Then convert the video using vision.VideoFileWriter to a .avi file

        videoFWriter = vision.VideoFileWriter([filename,'.avi'],'FrameRate',videoFReader.info.VideoFrameRate);
        while ~isDone(videoFReader)
            videoFrame = step(videoFReader);
            step(videoFWriter, videoFrame);
        end
        release(videoFReader);
        release(videoFWriter);