public void grayImage() throws IOException{
 File file = new File(System.getProperty("user.dir")+"/test.jpg");
 BufferedImage image = ImageIO.read(file);
  
 int width = image.getWidth(); 
 int height = image.getHeight(); 
  
 BufferedImage grayImage = new BufferedImage(width, height, BufferedImage.TYPE_BYTE_GRAY); 
 for(int i= 0 ; i < width ; i++){ 
  for(int j = 0 ; j < height; j++){ 
  int rgb = image.getRGB(i, j); 
  grayImage.setRGB(i, j, rgb); 
  } 
 } 
  
 File newFile = new File(System.getProperty("user.dir")+"/method1.jpg"); 
 ImageIO.write(grayImage, "jpg", newFile); 
}

img = cv2.imread('test.jpg',cv2.IMREAD_COLOR)
gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
cv2.imwrite('PythonMethod.jpg', gray)

img = cv2.imread('test.jpg',cv2.IMREAD_COLOR)
h, w = img.shape[:2]
gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
for j in range(w):
 for i in range(h):
  print str(i) + " : " + str(j) + " " + str(gray[i][j])
print img[h-1][w-1][0:3]

private static int colorToRGB(int alpha, int red, int green, int blue) {
 
  int newPixel = 0;
  newPixel += alpha;
  newPixel = newPixel << 8;
  newPixel += red;
  newPixel = newPixel << 8;
  newPixel += green;
  newPixel = newPixel << 8;
  newPixel += blue;
 
  return newPixel;
 
}
public static void main(String[] args) throws IOException {
 BufferedImage bufferedImage 
  = ImageIO.read(new File(System.getProperty("user.dir" + "/test.jpg"));
 BufferedImage grayImage = 
  new BufferedImage(bufferedImage.getWidth(), 
       bufferedImage.getHeight(), 
       bufferedImage.getType());
   
  
 for (int i = 0; i < bufferedImage.getWidth(); i++) {
  for (int j = 0; j < bufferedImage.getHeight(); j++) {
   final int color = bufferedImage.getRGB(i, j);
   final int r = (color >> 16) & 0xff;
   final int g = (color >> 8) & 0xff;
   final int b = color & 0xff;
   int gray = (int) (0.3 * r + 0.59 * g + 0.11 * b);;
   System.out.println(i + " : " + j + " " + gray);
   int newPixel = colorToRGB(255, gray, gray, gray);
   grayImage.setRGB(i, j, newPixel);
  }
 }
 File newFile = new File(System.getProperty("user.dir") + "/ok.jpg");
 ImageIO.write(grayImage, "jpg", newFile);
}