Extract color map from a video ?

Hi,

I try to follow this steps that I see in Matlab conference: https://www.mathworks.com/content/dam/mathworks/mathworks-dot-com/company/events/conferences/matlab-conference-australia/2017/proceedings/detecting-moving-objects-in-aerial-imagery-captured-from-unmanned-aerial-vehicles.pdf

And there I try to extract some points from a video using "detectSURFFeatures", for this case I use rgb2gray. But after all process, I get a modified image, named with '481x641xsingle' proprieties, but to use "foreground = step(foregroundDetector, videoFrame);" I need to transform it in '480x640x3xsingle', but I can't extract the color map from the video. How can I do that?

there is my code:

v = vision.VideoFileReader('C:\Users\rafae\Desktop\DRONE desafio street car.mp4');  

%%Create Video Player
videoPlayer = vision.VideoPlayer;
fgPlayer = vision.VideoPlayer;

%%Create Foreground Detector  (Background Subtraction)
foregroundDetector = vision.ForegroundDetector('NumGaussians', 3,'NumTrainingFrames', 50);

for i = 1:30

vidFrame = step(v);
I2 = rgb2gray(vidFrame);
point2 = detectSURFFeatures(I2);
[features2,valid_points2] = extractFeatures(I2,point2);

      if(rem(i,2)==0)

      if(rem(i,2)==0)
  vidFrame = step(v);
  I1=rgb2gray(vidFrame);
  point1=detectSURFFeatures(I1);
  [features1,valid_points1] = extractFeatures(I1,point1);
  % imshow(I1); hold on;
  % plot(point1.selectStrongest(10));
      else
  vidFrame = step(v);
  I2=rgb2gray(vidFrame);
  point2=detectSURFFeatures(I2);
  [features2,valid_points2] = extractFeatures(I2,point2);
  % imshow(I2); hold on;
  % plot(point2.selectStrongest(10));
      end
  indexPairs = matchFeatures(features1,features2);

matchedPoints1 = valid_points1(indexPairs(:,1),:);
matchedPoints2 = valid_points2(indexPairs(:,2),:);

%figure; showMatchedFeatures(I1,I2,matchedPoints1,matchedPoints2);

pointTracker = vision.PointTracker;

movingPoints = matchedPoints2.Location;
fixedPoints = matchedPoints1.Location;
tform = fitgeotrans(movingPoints,fixedPoints,'projective');

B = imwarp(I2,tform);

%frameDifferences = diff(framesWithWhiteBlobs);

      ind2gray

      videoFrame = step(B); %here is my error
      else
      videoFrame = step(v);
      end
      foreground = step(foregroundDetector,videoFrame);
  end