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

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.

Answer 1

[Walter Roberson]

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.

[Mona]

Thanks a lot for your answer Walter. I am not sure about if the videos are pseudocolored. If so, how to approach this? As for the shear, I tried to use

ycbcr2rgb(im)

but it still doesn't fix the problem. Appreciate your help, but do you have any more suggestions?

[Walter Roberson]

Please save one of the frames to a .mat file and attach it.

But in the meantime, try configuring http://www.mathworks.com/help/vision/ref/vision.videofilereader-class.html#bse_tfx-3 ImageColorSpace for VideoReader

[Mona]

Thanks a lot for trying to help me out. Attached is a frame of the video.

Also, I tried to use the vision video reader. So I used:

%
vidObj = vision.VideoFileReader(filename);
im=step(vidObj);
imshow(im)

And the image I get is fine, colored and not sheared/tilted. Only if I know how to extract specific frames of the video using step/vision.VideoFileReader

Also, looking at more examples, I now know the video frames don't even load as grayscale. It's another format that I cannot interpret! Take a look at the example below:

Thanks again

[Walter Roberson]

Could you show us the output of aviinfo applied to the file?

[Mona]

It's not an avi file, so I used:

vidObj = VideoReader(filename);

vidObj.VideoFormat

The returned format is RGB24

[Walter Roberson]

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]

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

Answer 2

[Mona]

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);

The .avi file now can be perfectly read in the correct format by VideoReader, and I cant choose which frames to process.