Java Graphics2D drawString 是 "blacking out"源图像

Question

这里是 Java 8 和 Mac OS (High Sierra)。我有以下类 TextOverlayer ，它从文件系统读取图像，并需要将一些红色文本覆盖到图像上，然后将该“覆盖”图像保存为文件系统上的不同文件:

public class TextOverlayer implements ImageObserver {

  public static void main(String[] args) throws IOException {

      // Instantiate a TextOverlayer and read a source/input image from disk
      TextOverlayer textOverlayer = new TextOverlayer();
      BufferedImage bufferedImage = ImageIO.read(Paths.get("/User/myuser/pix/sourceImage.jpg").toFile());

      // Lay some text over the image at specific coordinates
      BufferedImage drawn = textOverlayer.drawText(bufferedImage, "Some text");

      // Write the overlayed image to disk
      File outputfile = new File("/User/myuser/pix/targetImage.jpg");
      ImageIO.write(drawn, "jpg", outputfile);

  }

  private BufferedImage drawText(BufferedImage old, String text) {

      int w = old.getWidth() / 3;
      int h = old.getHeight() / 3;
      BufferedImage img = new BufferedImage(
              w, h, BufferedImage.TYPE_INT_ARGB);
      Graphics2D g2d = img.createGraphics();
      g2d.drawImage(old, 0, 0, w, h, this);
      g2d.setPaint(Color.red);
      g2d.setFont(new Font("Serif", Font.BOLD, 20));
      FontMetrics fm = g2d.getFontMetrics();
      int x = img.getWidth() - fm.stringWidth(text) - 5;
      int y = fm.getHeight();
      g2d.drawString(text, x, y);
      g2d.dispose();

      return img;

  }

  @Override
  public boolean imageUpdate(Image img, int infoflags, int x, int y, int width, int height) {
      return false;
  }

}

运行时，不会抛出任何错误，并且 targetImage.jpg 已成功写入磁盘，只不过它只是一个小黑盒的图像。我希望 targetImage.jpg 与 sourceImage.jpg 完全相同，只是在所需的坐标(图像内)添加了一些额外的文本。

有什么想法我会出错吗？

Answer 1

您不需要 ImageObserver，并且您可能无法使用附带的写入器将带有 Alpha channel 的图像写入 JPEG 文件。

这有效:

public class TextOverlayer {

    public static void main(String[] args) throws IOException {

        // Instantiate a TextOverlayer and read a source/input image from disk
        TextOverlayer textOverlayer = new TextOverlayer();
        BufferedImage bufferedImage = ImageIO.read(Paths.get("/User/myuser/pix/sourceImage.jpg").toFile());

        // Lay some text over the image at specific coordinates
        BufferedImage drawn = textOverlayer.drawText(bufferedImage, "Some text");

        // Write the overlayed image to disk
        File outputfile = new File("/User/myuser/pix/targetImage.jpg");
        boolean result = ImageIO.write(drawn, "jpg", outputfile);
        if (!result) {
            System.out.println("FAILED");
        }
    }

    private BufferedImage drawText(BufferedImage old, String text) {

        int w = old.getWidth();
        int h = old.getHeight();
        BufferedImage img = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
        Graphics2D g2d = img.createGraphics();
        g2d.drawImage(old, 0, 0, w, h, null);
        g2d.setPaint(Color.red);
        g2d.setFont(new Font("Serif", Font.BOLD, 20));
        FontMetrics fm = g2d.getFontMetrics();
        int x = img.getWidth() - fm.stringWidth(text) - 5;
        int y = fm.getHeight();
        g2d.drawString(text, x, y);
        g2d.dispose();

        return img;

    }
}