on rgbToGrayscaleImageFast (img)
  res = image(img.width, img.height, 8)
  res.paletteRef = #grayScale
  res.copyPixels(img, img.rect, img.rect)
  return res
end

on rgbToGrayscaleImageCustom (img)
  res = image(img.width, img.height, 8)
  res.paletteRef = #grayScale
  repeat with x = 0 to img.width-1
    repeat with y = 0 to img.height-1
      c = img.getPixel(x,y)
      n = c.red*0.2126 + c.green*0.7152 + c.blue*0.0722
      res.setPixel(x,y, color(256-n))
    end repeat
  end repeat
  return res
end