code: public static BufferedImage redraw(BufferedImage img, Color bg) {
          BufferedImage rgbImage = new BufferedImage(img.getWidth(),
                                                     img.getHeight(),
                                                     BufferedImage.TYPE_3BYTE_BGR);
          Graphics2D g2d = rgbImage.createGraphics();
          g2d.drawImage(img, 0, 0, bg, null);
          g2d.dispose();
          return rgbImage;
      }
docs: 在一个RGB画布上重新绘制Image,解决CMYK图像偏色的问题