[Java] grayscale로 이미지 저장하기

BufferedImage image = ImageIO.read(new File("input.png"));

for(int y = 0; y < image.getHeight(); y++) {
   for(int x = 0; x < image.getWidth(); x++) {
       Color colour = new Color(image.getRGB(x, y));
//       Choose one from below
//       int Y = (int) (0.299 * colour.getRed() + 0.587 * colour.getGreen() + 0.114 * colour.getBlue());
       int Y = (int) (0.2126 * colour.getRed() + 0.7152 * colour.getGreen() + 0.0722 * colour.getBlue());
       image.setRGB(x, y, new Color(Y, Y, Y).getRGB());
   }
}

ImageIO.write(image, "png", new File("output.png"));