docs: public static BufferedImage convertImageToGrayscale(BufferedImage image) {
          BufferedImage tmp = new BufferedImage(image.getWidth(), image.getHeight(), BufferedImage.TYPE_BYTE_GRAY);
          Graphics2D g2 = tmp.createGraphics();
          g2.drawImage(image, 0, 0, null);
          g2.dispose();
          return tmp;
      }