Convertion from grayscale value to RGB vector

Hello, I am trying to figure out how I have to convert a grayscale value which has been exracted from a grayscale frame of an avi video to the right RGB value (vector). I am using the code below:

if true
% Extract frames from video and save it on an Array
folder = fileparts(which('diffusion_process.avi'));
movieFullFileName= fullfile(folder,'diffusion_process.avi');
videoObject = VideoReader(movieFullFileName);
numberOfFrames = videoObject.NumberOfFrames;
for frame = 1:numberOfFrames
thisFrame = read(videoObject,frame);
if frame == 1
  h = size(thisFrame,1);
  w = size(thisFrame,2);
  processo = zeros(h, w, 3, numberOfFrames);
end
processo(:, :, :, frame) = thisFrame;
end
i = 1;
Color=[processo(X,Y,1,i),processo(X,Y,1,i),processo(X,Y,1,i)];
end

The vector called Color always returns white. I am not sure if I have set the RGB vector in the correct way. Any suggestions? Many thanks Davide

Answer 1

[Jan]

Your processo array is a double array with the range [0, 1], but the frames obtained from the movie might have the type INT8 with a range of 0:255. Then all but a 0 value produces a white color in the double array. Convert the types:

processo(:, :, :, frame) = im2double(thisFrame);

or:

processo(:, :, :, frame) = double(thisFrame) / 255;

[Guillaume]

Alternatively, create processo so that it is the same class as the frame:

    %in the if block
    processo = zeros(h, w, 3, numberOfFrames, 'like', thisFrame);

This will use less memory than converting the whole lot to double (8 times the memory of an uint8 array)

[Davide Magnelli]

Now Color = [0.8118 0.8118 0.8118] (18th frame for example) and is a light gray but I'd wish to obtain a RGB color. Is it possible?