Java implementation of drag and drop image clipping tutorial

This is an entry level article, please skip it.

In this article we will learn how to crop an image in Java and save the clipped parts separately to a file.

We will learn the following steps:

1. Enter the image and specify the image path to be processed
2. Allow users to drag and drop parts to be clipped
3. After selection, use the Robot class to determine the coordinates of the clipping part
4. Crop the selected image and hold it

Next we'll start coding.

Listing1: the imported class

import java.awt.Graphics;

import java.awt.Rectangle;

import java.awt.Robot;

import java.awt.event.MouseEvent;

import java.awt.event.MouseListener;

import java.awt.event.MouseMotionListener;

import java.awt.image.BufferedImage;

import java.io.File;

import javax.imageio.ImageIO;

import javax.swing.JFrame;

Description:

The Graphics class contains methods for drawing rectangles
2. We use the Rectangle class as the drag-out Rectangle area for cropping
3. The Robot class is used to capture screenshots
4. Use the mouse listener to get the drag time of the mouse
5. The Robot class USES BufferedImage for image processing
6.File class is used to open an image File
7. The ImageIO class is used to write images to PNG or JPG image files
8.JFrame is used to display the interface

Now let's write the entry class that contains the main method

Listing2: entrance class

public class CropImage extends JFrame implements MouseListener, MouseMotionListener

{

    int drag_status=0,c1,c2,c3,c4;

public static void main(String args[])

{

    new CropImage().start();

}

Description:

1. Wrote a class called CropImage
2. This class extends JFrame to implement all the functionality of a frame
3. Implement different mouse event listeners to know when the user starts dragging the mouse pointer
4. Drag_status variable is used to save the coordinates when the mouse starts dragging
5. We define the main method to call a start method, which is defined below

Next is the start method

Listing 2

public void start()

{

    ImagePanel im=new ImagePanel("F:\Wallpaper\wallpapers\1.jpg");

    add(im);

    setSize(400,400);

    setVisible(true);

    addMouseListener(this);

    addMouseMotionListener( this );

    setDefaultCloseOperation(EXIT_ON_CLOSE);

}

Description:

1. We define a class named ImagePanel that takes the image to be processed as an argument
2. Place the ImagePanel to display the image in the JFrame and start listening for mouse events

Let's define the methods for handling mouse events

Listing 3: mouse event handler

@Override

public void mouseClicked(MouseEvent arg0) {

}
@Override

public void mouseEntered(MouseEvent arg0) {

}
@Override

public void mouseExited(MouseEvent arg0) {

}
@Override

public void mousePressed(MouseEvent arg0) {

    repaint();

    c1=arg0.getX();

    c2=arg0.getY();

}
@Override

public void mouseReleased(MouseEvent arg0) {

    repaint();

    if(drag_status==1)

    {

    c3=arg0.getX();

    c4=arg0.getY();

    try

    {

    draggedScreen();

    }

    catch(Exception e)

    {

        e.printStackTrace();

    }

    }

}
@Override

public void mouseDragged(MouseEvent arg0) {

    repaint();

    drag_status=1;

    c3=arg0.getX();

    c4=arg0.getY();

}
@Override

public void mouseMoved(MouseEvent arg0) {
}
public void paint(Graphics g)

{

    super.paint(g);

    int w = c1 - c3;

    int h = c2 - c4;

    w = w * -1;

    h = h * -1;

    if(w<0)

        w = w * -1;

    g.drawRect(c1, c2, w, h);
}

Description:

1. Store the current coordinates to c1 and c2 when the mouse is pressed
2. Set the drag status variable drag_status to true when the mouse is pressed and started to drag
3. When the mouse button is released, the clipping area of the image has been selected, and draggedscreen method is called
4. Paint method is used to display the rectangle when dragging, drawing the rectangle by the current coordinates and the coordinates of the initial record

Here is the code for the draggedscreen method

Listing 4: draggedScreen method

public void draggedScreen()throws Exception

{

        int w = c1 - c3;

        int h = c2 - c4;

        w = w * -1;

        h = h * -1;

        Robot robot = new Robot();

        BufferedImage img = robot.createScreenCapture(new Rectangle(c1, c2,w,h));

        File save_path=new File("screen1.jpg");

        ImageIO.write(img, "JPG", save_path);

    System.out.println("Cropped image saved successfully.");

}}

Description:

1. First, calculate the height and width of the image
2. Use the Robot class to take a screenshot of the clipped area and save it to another file, screen1.jpg

Complete code

Listing 5: ImagePanel. Java

import java.awt.Dimension;

import java.awt.Graphics;

import java.awt.Image;
import javax.swing.ImageIcon;

import javax.swing.JPanel;
    class ImagePanel extends JPanel {
          private Image img;
          public ImagePanel(String img) {

            this(new ImageIcon(img).getImage());

          }
          public ImagePanel(Image img) {

            this.img = img;

            Dimension size = new Dimension(img.getWidth(null), img.getHeight(null));

           // Dimension size = new Dimension(10,10);

            setPreferredSize(size);

            setMinimumSize(size);

            setMaximumSize(size);

            setSize(size);

            setLayout(null);

          }
          public void paintComponent(Graphics g) {

            g.drawImage(img, 0, 0, null);

          }
        }

Listing 6: CropImage. Java

import java.awt.Graphics;

import java.awt.Rectangle;

import java.awt.Robot;

import java.awt.event.MouseEvent;

import java.awt.event.MouseListener;

import java.awt.event.MouseMotionListener;

import java.awt.image.BufferedImage;

import java.io.File;

import javax.imageio.ImageIO;

import javax.swing.JFrame;
public class CropImage extends JFrame implements MouseListener, MouseMotionListener

{

    int drag_status=0,c1,c2,c3,c4;

public static void main(String args[])

{

    new CropImage().start();

}

public void start()

{

    ImagePanel im=new ImagePanel("F:\Wallpaper\wallpapers\1.jpg");

    add(im);

    setSize(400,400);

    setVisible(true);

    addMouseListener(this);

    addMouseMotionListener( this );

    setDefaultCloseOperation(EXIT_ON_CLOSE);

}

public void draggedScreen()throws Exception

{

        int w = c1 - c3;

        int h = c2 - c4;

        w = w * -1;

        h = h * -1;

        Robot robot = new Robot();

        BufferedImage img = robot.createScreenCapture(new Rectangle(c1, c2,w,h));

        File save_path=new File("screen1.jpg");

        ImageIO.write(img, "JPG", save_path);

    System.out.println("Cropped image saved successfully.");

}

@Override

public void mouseClicked(MouseEvent arg0) {

}
@Override

public void mouseEntered(MouseEvent arg0) {

}
@Override

public void mouseExited(MouseEvent arg0) {

}
@Override

public void mousePressed(MouseEvent arg0) {

    repaint();

    c1=arg0.getX();

    c2=arg0.getY();

}
@Override

public void mouseReleased(MouseEvent arg0) {

    repaint();

    if(drag_status==1)

    {

    c3=arg0.getX();

    c4=arg0.getY();

    try

    {

    draggedScreen();

    }

    catch(Exception e)

    {

        e.printStackTrace();

    }

    }

}
@Override

public void mouseDragged(MouseEvent arg0) {

    repaint();

    drag_status=1;

    c3=arg0.getX();

    c4=arg0.getY();

}
@Override

public void mouseMoved(MouseEvent arg0) {
}
public void paint(Graphics g)

{

    super.paint(g);

    int w = c1 - c3;

    int h = c2 - c4;

    w = w * -1;

    h = h * -1;

    if(w<0)

        w = w * -1;

    g.drawRect(c1, c2, w, h);

}

}