ZXing生成二维码水印变黑白的原因及解决方法是什么？

import com.google.zxing.*; import com.google.zxing.common.BitMatrix; import com.google.zxing.qrcode.QRCodeWriter; import net.coobird.thumbnailator.Thumbnails; import net.coobird.thumbnailator.geometry.Positions;  import javax.imageio.ImageIO; import java.awt.*; import java.awt.image.BufferedImage; import java.io.File; import java.io.IOException;  public class QRCodeWatermarkExample {     public static void main(String[] args) throws WriterException, IOException {         // 生成二维码         QRCodeWriter qrCodeWriter = new QRCodeWriter();         BitMatrix bitMatrix = qrCodeWriter.encode("https://example.com", BarcodeFormat.QR_CODE, 300, 300);          BufferedImage qrCodeImage = toBufferedImage(bitMatrix);          // 转换为高位深度 BufferedImage         BufferedImage convertedImage = new BufferedImage(qrCodeImage.getWidth(), qrCodeImage.getHeight(), BufferedImage.TYPE_INT_RGB);         Graphics2D g2d = convertedImage.createGraphics();         g2d.drawImage(qrCodeImage, 0, 0, null);         g2d.dispose();          // 读取水印图片         BufferedImage watermarkImage = ImageIO.read(new File("path/to/watermark/image.png"));          // 使用 Thumbnailator 添加水印         BufferedImage watermarkedImage = Thumbnails.of(convertedImage)                 .size(300, 300)                 .watermark(Positions.BOTTOM_RIGHT, watermarkImage, 0.5f)                 .asBufferedImage();          // 保存最终图像         ImageIO.write(watermarkedImage, "png", new File("output.png"));     }      private static BufferedImage toBufferedImage(BitMatrix matrix) {         int width = matrix.getWidth();         int height = matrix.getHeight();         BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_BYTE_BINARY);         // ... (toBufferedImage 方法内容与原文相同) ...     } }