How do I crop an image in Java?

java

I want to crop an image manually using the mouse.
Suppose the image has some text, and I want to select some text from an image, then for that purpose I want to crop that area by using the mouse.

The solution I found most useful for cropping a buffered image uses the getSubImage(x,y,w,h);

My cropping routine ended up looking like this:

  private BufferedImage cropImage(BufferedImage src, Rectangle rect) {
      BufferedImage dest = src.getSubimage(0, 0, rect.width, rect.height);
      return dest; 
   }

There are two potentially major problem with the leading answer to this question. First, as per the docs:

public BufferedImage getSubimage(int x, int y, int w, int h)

Returns a subimage defined by a specified rectangular region. The returned BufferedImage shares the same data array as the original image.

Essentially, what this means is that result from getSubimage acts as a pointer which points at a subsection of the original image.

Why is this important? Well, if you are planning to edit the subimage for any reason, the edits will also happen to the original image. For example, I ran into this problem when I was using the smaller image in a separate window to zoom in on the original image. (kind of like a magnifying glass). I made it possible to invert the colors to see certain details more easily, but the area that was "zoomed" also got inverted in the original image! So there was a small section of the original image that had inverted colors while the rest of it remained normal. In many cases, this won't matter, but if you want to edit the image, or if you just want a copy of the cropped section, you might want to consider a method.

Which brings us to the second problem. Fortunately, it is not as big a problem as the first. getSubImage shares the same data array as the original image. That means that the entire original image is still stored in memory. Assuming that by "crop" the image you actually want a smaller image, you will need to redraw it as a new image rather than just get the subimage.

Try this:

BufferedImage img = image.getSubimage(startX, startY, endX, endY); //fill in the corners of the desired crop location here
BufferedImage copyOfImage = new BufferedImage(img.getWidth(), img.getHeight(), BufferedImage.TYPE_INT_RGB);
Graphics g = copyOfImage.createGraphics();
g.drawImage(img, 0, 0, null);
return copyOfImage; //or use it however you want

This technique will give you the cropped image you are looking for by itself, without the link back to the original image. This will preserve the integrity of the original image as well as save you the memory overhead of storing the larger image. (If you do dump the original image later)

This is a method which will work:

import java.awt.image.BufferedImage;
import java.awt.Rectangle;
import java.awt.Color;
import java.awt.Graphics;

public BufferedImage crop(BufferedImage src, Rectangle rect)
{
    BufferedImage dest = new BufferedImage(rect.getWidth(), rect.getHeight(), BufferedImage.TYPE_ARGB_PRE);
    Graphics g = dest.getGraphics();
    g.drawImage(src, 0, 0, rect.getWidth(), rect.getHeight(), rect.getX(), rect.getY(), rect.getX() + rect.getWidth(), rect.getY() + rect.getHeight(), null);
    g.dispose();
    return dest;
}

Of course you have to make your own JComponent:

import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.image.BufferedImage;
import java.awt.Rectangle;
import java.awt.Graphics;
import javax.swing.JComponent;

public class JImageCropComponent extends JComponent implements MouseListener, MouseMotionListener
{
   private BufferedImage img;
   private int x1, y1, x2, y2;

   public JImageCropComponent(BufferedImage img)
   {
       this.img = img;
       this.addMouseListener(this);
       this.addMouseMotionListener(this);
   }

   public void setImage(BufferedImage img)
   {
       this.img = img;
   }

   public BufferedImage getImage()
   {
       return this;
   }

   @Override
   public void paintComponent(Graphics g)
   {
      g.drawImage(img, 0, 0, this);
      if (cropping)
      {
          // Paint the area we are going to crop.
          g.setColor(Color.RED);
          g.drawRect(Math.min(x1, x2), Math.min(y1, y2), Math.max(x1, x2), Math.max(y1, y2));
      }
   }

   @Override
   public void mousePressed(MouseEvent evt)
   {
       this.x1 = evt.getX();
       this.y1 = evt.getY();
   }

   @Override
   public void mouseReleased(MouseEvent evt)
   {
       this.cropping = false;
       // Now we crop the image;
       // This is the method a wrote in the other snipped
       BufferedImage cropped = crop(new Rectangle(Math.min(x1, x2), Math.min(y1, y2), Math.max(x1, x2), Math.max(y1, y2));
       // Now you have the cropped image;
       // You have to choose what you want to do with it
       this.img = cropped;
   }

   @Override
   public void mouseDragged(MouseEvent evt)
   {
       cropping = true;
       this.x2 = evt.getX();
       this.y2 = evt.getY();
   }

   //TODO: Implement the other unused methods from Mouse(Motion)Listener

}

I didn't test it. Maybe there are some mistakes (I'm not sure about all the imports).

You can put the crop(img, rect) method in this class. Hope this helps.

How do I crop an image in Java?

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