java 图像在 JPanel 或 JLabel 中调整大小和显示而不会降低质量

Image resizing and displaying in a JPanel or a JLabel without loss of quality

提问by Dilshan Ranaweera

I'm developing a java program to capture employee images at the time of registration using a webcam. I can obtain the picture without any problem, and save it in my C: drive but upon retrieval of the image only a part of the image is displayed on the label. Is there a way of re sizing the JPEG before saving it? or before displaying it? like shrinking it without a quality loss....

我正在开发一个 Java 程序来使用网络摄像头在注册时捕获员工图像。我可以毫无问题地获取图片，并将其保存在我的 C: 驱动器中，但在检索图像时，标签上仅显示图像的一部分。有没有办法在保存之前调整 JPEG 的大小？还是在显示之前？就像在没有质量损失的情况下缩小它......

Thankz a lot Cheerz! :)!

非常感谢Cheerz！:)！

okay guys... here goes:- I have commented the code in the way I have used them.

好吧，伙计们......这里是：-我已经按照我使用它们的方式对代码进行了评论。

//This method will capture the image from the interface and save it under the unique employee ID
public String captureImage(int picId){

    FrameGrabbingControl ControlFG = (FrameGrabbingControl)

    broadcast.getControl("javax.media.control.FrameGrabbingControl");

    Buffer buffer = ControlFG.grabFrame();

    BufferToImage image = new BufferToImage((VideoFormat)buffer.getFormat());

    img = image.createImage(buffer);

    path="c:\employee"+picId+".jpg";

    saveJPG(img,path);//method will save the image

    return path;

}

 public void saveJPG(Image img, String s){***//method will save the image***

    System.out.println(s);

    BufferedImage bi = new BufferedImage(img.getWidth(null), img.getHeight(null),

    BufferedImage.TYPE_INT_RGB);

    Graphics2D g2 = bi.createGraphics();

    g2.drawImage(img,null,null);

    FileOutputStream out = null;
    try{

    out = new FileOutputStream(s);

    }
    catch (java.io.FileNotFoundException io){

    System.out.println("File Not Found");
    }

    JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);

    JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(bi);

    param.setQuality(0.5f,false);

    encoder.setJPEGEncodeParam(param);

    try
    {
    encoder.encode(bi);
    out.close();
    }

    catch (java.io.IOException io)
    {
    System.out.println("IOException");
    }
    }

maybe I can scale the image while saving.. so that I can retrieve the scaled image..

也许我可以在保存时缩放图像..以便我可以检索缩放的图像..

回答by David Kroukamp

Of course you can resize the image there are many different ways like Image#getScaledInstance(int width,int height,int hints), but this has its perils.

当然，您可以通过多种不同的方式来调整图像大小Image#getScaledInstance(int width,int height,int hints)，但这有其危险。

The main problem being:

主要问题是：

Image.getScaledInstance() does not return a finished, scaled image. It leaves much of the scaling work for a later time when the image pixels are used.

Image.getScaledInstance() 不返回完成的缩放图像。当使用图像像素时，它将大部分缩放工作留到以后进行。

I would not recommend using it but hereis a nice example.

我不推荐使用它，但这里有一个很好的例子。

Alternatively you can use this method:

或者，您可以使用此方法：

import javax.swing.ImageIcon;
import java.awt.image.BufferedImage;
import java.awt.Image;
import java.awt.Color;
import java.awt.Graphics2D;
import java.io.File;
import javax.imageio.ImageIO;
import java.awt.RenderingHints;

public class ImgUtils {

public BufferedImage scaleImage(int WIDTH, int HEIGHT, String filename) {
    BufferedImage bi = null;
    try {
        ImageIcon ii = new ImageIcon(filename);//path to image
        bi = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
        Graphics2D g2d = (Graphics2D) bi.createGraphics();
        g2d.addRenderingHints(new RenderingHints(RenderingHints.KEY_RENDERING,RenderingHints.VALUE_RENDER_QUALITY));
        g2d.drawImage(ii.getImage(), 0, 0, WIDTH, HEIGHT, null);
    } catch (Exception e) {
        e.printStackTrace();
        return null;
    }
    return bi;
}

}

you'd use it like:

你会像这样使用它：

final BufferedImage img=new ImgUtils().scaleImage(200,200,"c:/test.jpg");
//create label with image as background
JLabel label=new JLabel(new ImageIcon((Image)img));

UPDATE:

更新：

Here is a small example I made:

这是我制作的一个小例子：

import java.awt.BorderLayout;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.RenderingHints;
import java.awt.image.BufferedImage;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingUtilities;

public class JavaApplication117 {

    //change this to your own
    static String filename="c:/test.jpg";

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

            @Override
            public void run() {
                new JavaApplication117().createAndShowUI();
            }
        });
    }

    private void createAndShowUI() {
        JFrame frame = new JFrame("Test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        initComponents(frame);

        frame.setResizable(false);
        frame.pack();
        frame.setVisible(true);
    }

    private void initComponents(JFrame frame) {
        final BufferedImage img = new ImgUtils().scaleImage(200, 200, filename);
        //create label with image as background
        JLabel label = new JLabel(new ImageIcon((Image) img));

        frame.getContentPane().add(label, BorderLayout.CENTER);
    }
}

class ImgUtils {

    public BufferedImage scaleImage(int WIDTH, int HEIGHT, String filename) {
        BufferedImage bi = null;
        try {
            ImageIcon ii = new ImageIcon(filename);//path to image
            bi = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
            Graphics2D g2d = (Graphics2D) bi.createGraphics();
            g2d.addRenderingHints(new RenderingHints(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY));
            g2d.drawImage(ii.getImage(), 0, 0, WIDTH, HEIGHT, null);
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
        return bi;
    }
}

References:

参考：

• resizing image java getScaledInstance

• 调整图像大小 java getScaledInstance