Maintain aspect ratio when resizing an image and resizing jPanel at the same time

Question

I'm trying to maintain aspect ratio by calculating width percentage and height percentage of the original image and then set the new height and new width based on percentages but there is something wrong in my code :

import javax.imageio.ImageIO;
import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.net.URL;

public class Test extends JFrame {
private JPanel principalPanel;
private BufferedImage image;
public Test() {
    setSize(600,600);
    setLocationRelativeTo(null);
    setDefaultCloseOperation(EXIT_ON_CLOSE);

    try {
        URL url = new 
       URL("https://boygeniusreport.files.wordpress.com/2017/04/earth.jpg");
        image = ImageIO.read(url);
    } catch (Exception e) {
        System.out.println("Problem loading image");
        e.printStackTrace();
    }
    principalPanel = new JPanel() {
        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            int width = image.getWidth();
            int height = image.getHeight();
            int wPercentage = (width*100)/(width+height);
            int hPercentage = (height*100)/(width+height);
            int w = (width+((getHeight()-height)*wPercentage)/hPercentage);
            int h = (height+((getWidth()-width)*hPercentage)/wPercentage);
            g.drawImage(image,0,0,w,h,this);
        }
    };
    setContentPane(principalPanel);
    setVisible(true);
}
public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
        @Override
        public void run() {
            new Test();
        }
    });
}
}

You need to get the ratio of image height to width, and then maintain this ratio -- you're not doing this as I don't see you calculating this ration in your code above. `width + height` has no place in these calculations. — DontKnowMuchBut Getting Better, Apr 12 '18 at 16:56
Some examples [here](https://stackoverflow.com/q/15961412/230513). — trashgod, Apr 12 '18 at 17:12

score 0 · Answer 1 · answered Apr 12 '18 at 20:34

Here is the solution:

import javax.imageio.ImageIO;
import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.net.URL;

public class Test extends JFrame {
private JPanel principalPanel;
private BufferedImage image;
public Test() {
    setSize(600,600);
    setLocationRelativeTo(null);
    setDefaultCloseOperation(EXIT_ON_CLOSE);

    try {
        URL url = new
                URL("https://boygeniusreport.files.wordpress.com/2017/04/earth.jpg");
        image = ImageIO.read(url);
    } catch (Exception e) {
        System.out.println("Problem loading image");
        e.printStackTrace();
    }
    principalPanel = new JPanel() {
        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            int original_width = image.getWidth();
            int original_height = image.getHeight();
            int bound_width = getWidth();
            int bound_height = getHeight();
            int new_width = original_width;
            int new_height = original_height;

            // first check if we need to scale width
            if (original_width > bound_width) {
                //scale width to fit
                new_width = bound_width;
                //scale height to maintain aspect ratio
                new_height = (new_width * original_height) / original_width;
            }

            // then check if we need to scale even with the new height
            if (new_height > bound_height) {
                //scale height to fit instead
                new_height = bound_height;
                //scale width to maintain aspect ratio
                new_width = (new_height * original_width) / original_height;
            }
            g.drawImage(image,0,0,new_width,new_height,this);
        }
    };
    setContentPane(principalPanel);
    setVisible(true);
}
public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
        @Override
        public void run() {
            new Test();
        }
    });
}
}

Maintain aspect ratio when resizing an image and resizing jPanel at the same time

1 Answers1