来自JPanel的BufferedImage具有透明背景

Question

我正在尝试在我的onPaint方法中显示图像，但不断获得黑色背景。我显示的图像是JPanel.print（Graphics）或JPanel.paint（Graphics）的结果。所以我将此结果转换为png文件，该文件存储在数据库中。稍后，该图像由用户加载和转换。这个过程给了我一个黑色的背景。

以下是代码：

首先创建图像：

    public static BufferedImage createBufferedImageFromView(JPanel panel){
    int w = panel.getWidth();
    int h = panel.getHeight();
    BufferedImage bi = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
    Graphics2D g = bi.createGraphics();

    g.setBackground(new Color(0, 0, 0, 0));
    g.clearRect(0, 0, bi.getWidth(), bi.getHeight());
    g.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_IN, 0.0f));

    panel.setOpaque(false);
    panel.repaint();
    panel.print(g);

    return bi;
}

然后我在onPaint（）方法中绘制它：

public void paint(Graphics g) {
super.paint(g);

    ParameterBlock params = new ParameterBlock();
    params.addSource(previewImage); //source is the input image
    int w = previewImage.getWidth(); //Set to the original width of the image
    int h = previewImage.getHeight(); //Set to the original height of image

    Point tl = new Point((int)cornersTrans[0].getX(), (int)cornersTrans[0].getY()); //The new top left corner
    Point tr = new Point((int)cornersTrans[1].getX(), (int)cornersTrans[1].getY()); //The new top right corner
    Point bl = new Point((int)cornersTrans[2].getX(), (int)cornersTrans[2].getY()); //The new bottom left corner
    Point br = new Point((int)cornersTrans[3].getX(), (int)cornersTrans[3].getY()); //The new bottom right corner
    try {
        params.add(new WarpPerspective(PerspectiveTransform.getQuadToQuad(0,0, 0, h, w, h, w, 0, tl.x, tl.y, bl.x, bl.y, br.x, br.y, tr.x, tr.y).createInverse()));
    } catch (NoninvertibleTransformException e) {
        e.printStackTrace();
    } catch (CloneNotSupportedException e) {
        e.printStackTrace();
    }

    if(!isInMovement)
        params.add(Interpolation.getInstance(Interpolation.INTERP_BICUBIC)); 

    PlanarImage image = JAI.create("warp", params);

    int y0 = (int) (cornersTrans[0].getY() < cornersTrans[1].getY() ? cornersTrans[0].getY() : cornersTrans[1].getY());
    int x0 = (int) (cornersTrans[0].getX() < cornersTrans[2].getX() ? cornersTrans[0].getX() : cornersTrans[2].getX());
    int x1 = (int) (cornersTrans[3].getX() > cornersTrans[1].getX() ? cornersTrans[3].getX() : cornersTrans[1].getX());
    int y1 = (int) (cornersTrans[3].getY() > cornersTrans[2].getY() ? cornersTrans[3].getY() : cornersTrans[2].getY());

    Graphics2D g2d = (Graphics2D) g;

// g2d.setBackground（new Color（0,255,0,0））; // g2d.clearRect（0,0,9999,9999）;         g2d.drawImage（（Image）image.getAsBufferedImage（），x0，y0，x1，y1,0,0，image.getWidth（），image.getHeight（），null）;

有关如何修复黑色背景的想法吗？

谢谢！