java - 如何使用java从图像中去除白色矩形

Question

我厌倦了下面的代码来生成缩略图，但是当我把它放在另一个图像上时，缩略图有一个白色的矩形。如何使用 java graphics 2D 删除它？

  Image image = javax.imageio.ImageIO.read(new File(originalFile));       
  BufferedImage thumbImage = new BufferedImage(thumbWidth, thumbHeight, BufferedImage.TYPE_INT_RGB);
  Graphics2D graphics2D = thumbImage.createGraphics();
  graphics2D.setBackground(Color.WHITE);
  graphics2D.setPaint(Color.WHITE); 
  graphics2D.fillRect(0, 0, thumbWidth, thumbHeight);       
  graphics2D.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
  graphics2D.drawImage(image, 0, 0, thumbWidth, thumbHeight, null);   
  File file = new File(thumbnailFile);
  if(javax.imageio.ImageIO.write(thumbImage, "png", file))
      return file;
  }

即使我删除这三行，我也会得到黑色矩形。

 graphics2D.setBackground(Color.WHITE);
 graphics2D.setPaint(Color.WHITE); 
 graphics2D.fillRect(0, 0, thumbWidth, thumbHeight);   

如何让这张图片变透明？请有人帮助我。

Answer 1

 Color transparent = new Color(0,0,0,0)

通过设置 Composite 。 here : AlphaComposite

 // Create an image that supports arbitrary levels of transparency
 Graphics2D g2d = (Graphics2D) image.getGraphics();
 BufferedImage thumbImage = g2d.getDeviceConfiguration().createCompatibleImage(
    thumbWidth, thumbHeight, Transparency.TRANSLUCENT);