How do I determine RGB values for a single column of an image?

I have a video with over 2000 frames (1080x1920x3) and I want to determine the RGB values of all the frames at column 600.

I need to have 3 matrix with size [1080(rows), 2000(numberofFrames)] for red , green, and blue.

The following is my code. The matrix dimensions do not match and I don't know how to resolve it.

clc;    
close all;  
imtool close all;  
clear;  
workspace;  
fontSize = 22;

folder = fileparts(which('pan-head.mp4'));
movieFullFileName = fullfile(folder, 'pan-head.mp4');
 if ~exist(movieFullFileName, 'file')
    strErrorMessage = sprintf('File not found:\n%s\nYou can choose a new one, or cancel', movieFullFileName);
    response = questdlg(strErrorMessage, 'File not found', 'OK - choose a new movie.', 'Cancel', 'OK - choose a new movie.');
    if strcmpi(response, 'OK - choose a new movie.')
        [baseFileName, folderName, FilterIndex] = uigetfile('*.avi');
        if ~isequal(baseFileName, 0)
            movieFullFileName = fullfile(folderName, baseFileName);
        else
            return;
        end
    else
        return;
    end
end
    videoObject = VideoReader(movieFullFileName)
    numberOfFrames = videoObject.NumberOfFrames;
    vidHeight = videoObject.Height;
    vidWidth = videoObject.Width;

      numberOfFramesWritten = 0;

     figure;

      set(gcf, 'units','normalized','outerposition',[0 0 1 1]);

      promptMessage = sprintf('Do you want to save the individual frames out to individual disk files?');
      button = questdlg(promptMessage, 'Save individual frames?', 'Yes', 'No', 'Yes');
      if strcmp(button, 'Yes')
          writeToDisk = true;       
          [folder, baseFileName, extentions] = fileparts(movieFullFileName);
          folder = pwd;   % Make it a subfolder of the folder where this m-file lives.
          outputFolder = sprintf('%s/Movie Frames from %s', folder, baseFileName);

          if ~exist(outputFolder, 'dir')
              mkdir(outputFolder);
          end
      else
          writeToDisk = false;
      end
       for frame = 1 : numberOfFrames

          thisFrame = read(videoObject, frame);

          hImage = subplot(2, 2, 1);
          image(thisFrame);
          caption = sprintf('Frame %4d of %d.', frame, numberOfFrames);
          title(caption, 'FontSize', fontSize);
          drawnow; %refresh the window.

          % Write the image array to the output file
          %if writeToDisk
              % Construct an output image file name.
              outputBaseFileName = sprintf('Frame %4.4d.png', frame);
              outputFullFileName = fullfile(outputFolder, outputBaseFileName);

             frameWithText = getframe(gca);

              imwrite(frameWithText.cdata, outputFullFileName, 'png');
      end
  m = [vidHeight, numberOfFrames, 3]

for i = 1:1:numberOfFrames;

red(i) = reshape(m(:,600,1),1,[]);
green(i) = reshape(m(:,600,1),1,[]);
blue (i) = reshape(m(:,600,1),1,[]);

end

Can anyone explain what the exact problem is?

Is there any other approach that I can adopt?

Thanks a lot :)

Answer 1

[Image Analyst]

Before the loop, you preallocate your R, G, and B arrays

redColumn600s = zeros(vidHeight, numberOfFrames, 'uint8');
greenColumn600s = zeros(vidHeight, numberOfFrames, 'uint8');
blueColumn600s = zeros(vidHeight, numberOfFrames, 'uint8');

You get your single frame from this:

thisFrame = read(videoObject, frame);

so now you need to extract column 600. To get the 3 colors separately, you'd do this:

column600R = thisFrame(:, 600, 1); % Extract red channel column 600.
column600G = thisFrame(:, 600, 2); % Extract green channel column 600.
column600B = thisFrame(:, 600, 3); % Extract blue channel column 600.

Then stuff those into your cumulative arrays

redColumn600s(:, frame) = column600R;
greenColumn600s(:, frame) = column600G;
blueColumn600s(:, frame) = column600B;

(You could combine the last two code chunks if you want to eliminate the temporary vector variables.)

[meri mak]

thank you so much. I've got the results and I checked some of the random pixel's RGB values and they are totally valid.