Octave function to convert BMP image to grayscale matrix on [-1,1]

Question

For a university assignment, we were given a MATLAB/Octave toolbox. This includes the following function which should, in theory, read a BMP file and convert it to a matrix, with all values in [-1,1] where -1 means white and 1 means black.

function In=loadCNN(filename)
  Img=double(imread(filename));
  if size(Img,3)==3
    Img=(Img(:,:,1)+Img(:,:,2)+Img(:,:,3))/3;
  end     
  In=((double(Img)/127.5)-1)*-1;
end

However it does not work correctly, returning a matrix with, for example, 0.99216 for white pixels on this image:

Please help me write a function to do this. It should also work for colored BMPs, where it should be converted to grayscale first.

Answer 1

I think this should work for all bmp image...

function In=loadCNN(filename)
    Img=double(imread(filename));
    if size(Img,3)==3
        Img=mean(Img,3)/255;
    end
    In=2*Img-1
end