我正在写一个测试应用程序.要为图像设置Alpha,我使用paintComponent方法.观看下一个片段……

    public class TestImage extends JLabel{

        public void paintComponent( Graphics g ) {

                    super.paintComponent( g );

                    Graphics2D g2d=(Graphics2D)g;
                    g2d.drawImage(this.bImage, rop, 0, 0);


            }

    public void setRescaleOp(RescaleOp rop){this.rop=rop;}
}

如你看到的,

g2d.drawImage(this.bImage, rop, 0, 0);

不允许设置宽度和高度,就像我使用g.drawImage(bImage,0,0,width,height,null);

所以问题是……在这种情况下如何设置bImage的宽度和高度？

任何有用的评论表示赞赏

安德鲁

解决方法:

首先过滤(),如图here所示,然后使用drawImage()或AffineTransformOp进行缩放,如图here所示.

附录：或者,您可以先缩放图像(使用上述任一方法),然后在drawImage()中使用RescaleOp.

另外,RescaleOp缩放图像的色带;它不会改变图像的尺寸.为避免混淆,有时将尺寸缩放称为 resampling.

附录：这是使用drawImage()重新采样的示例,以及使用RescaleOp调整图像的alpha的示例.

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.awt.image.RescaleOp;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

/**
 * @see https://*.com/questions/5838842
 * @see https://*.com/questions/5864490
 */
public class AlphaTest {

    private static void display() {
        JFrame f = new JFrame("AlphaTest");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        ImageIcon icon = new ImageIcon("image.jpg");
        final AlphaPanel ip = new AlphaPanel(icon, 0.75);
        final JSlider slider = new JSlider();
        slider.addChangeListener(new ChangeListener() {

            @Override
            public void stateChanged(ChangeEvent e) {
                int v = slider.getValue();
                ip.setAlpha((float) v / slider.getMaximum());
                ip.repaint();
            }
        });
        f.add(ip, BorderLayout.CENTER);
        f.add(slider, BorderLayout.SOUTH);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                display();
            }
        });
    }
}

class AlphaPanel extends JPanel {

    private BufferedImage bi;
    private float[] scales = {1f, 1f, 1f, 0.5f};
    private float[] offsets = new float[4];
    private RescaleOp rop;

    public AlphaPanel(ImageIcon icon, double scale) {

        int width = (int) (scale * icon.getIconWidth());
        int height = (int) (scale * icon.getIconHeight());
        this.setPreferredSize(new Dimension(width, height));
        this.bi = new BufferedImage(
            width, height, BufferedImage.TYPE_INT_ARGB);
        this.bi.createGraphics().drawImage(
            icon.getImage(), 0, 0, width, height, null);
        rop = new RescaleOp(scales, offsets, null);
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        g2d.drawImage(bi, rop, 0, 0);
    }

    public void setAlpha(float alpha) {
        this.scales[3] = alpha;
        this.rop = new RescaleOp(scales, offsets, null);
    }
}