function gray = rgb2gray (rgb)
    switch(class(rgb))
    case "double"
      gray = luminance(rgb);
    case "uint8"
      gray = uint8(luminance(rgb));
    case "uint16"
      gray = uint16(luminance(rgb));
    endswitch
endfunction

function lum = luminance(rgb)
   lum = 0.2126*rgb(:,:,1) + 0.7152*rgb(:,:,2) + 0.0722*rgb(:,:,3);
endfunction