code: public static int getGray(BufferedImage srcIm, int x, int y) {
          int grayValue = getLuminance(srcIm, x, y);
          int newPixel = 0;
          newPixel = (grayValue << 16) & 0x00ff0000 | (newPixel & 0xff00ffff);
          newPixel = (grayValue << 8) & 0x0000ff00 | (newPixel & 0xffff00ff);
          newPixel = (grayValue) & 0x000000ff | (newPixel & 0xffffff00);
          return newPixel;
      }
docs: 获取图片指定像素点的灰度值
  
  @param srcIm
  源图片
  @param x
  横坐标
  @param y
  纵坐标
  @return 灰度值