Scale the ImageIcon automatically to label size

Question

On my JFrame, I am using the following code to display an image on the Panel :

  ImageIcon img= new ImageIcon(\"res.png\");
  jLabel.setIcon(img);


        

Answer 1

You can use the Stretch Icon.

The image will automatically be resized to fill the space available to the label. You can control whether the image is scaled proportionally or completely fills the area.

Using the StretchIcon is more flexible than doing custom painting as suggested in the other links as you can benefit from the automatic resizing on any component that supports an Icon.

StretchIcon.java:

import java.awt.Component;
import java.awt.Container;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Insets;
import java.awt.RenderingHints;
import java.awt.image.BufferedImage;
import java.awt.image.ImageObserver;
import java.net.URL;

import javax.swing.ImageIcon;

/**
 * An <CODE>Icon</CODE> that scales its image to fill the component area, excluding any border or insets, optionally maintaining the image's
 * aspect ratio by padding and centering the scaled image horizontally or vertically.
 * <P>
 * The class is a drop-in replacement for <CODE>ImageIcon</CODE>, except that the no-argument constructor is not supported.
 * <P>
 * As the size of the Icon is determined by the size of the component in which it is displayed, <CODE>StretchIcon</CODE> must only be used
 * in conjunction with a component and layout that does not depend on the size of the component's Icon.
 *
 * @version 1.1 01/15/2016
 * @author Darryl
 */
public class StretchIcon extends ImageIcon
{
    /**
     *
     */
    private static final long serialVersionUID = 1L;
    /**
     * Determines whether the aspect ratio of the image is maintained. Set to <code>false</code> to allow th image to distort to fill the
     * component.
     */
    protected boolean         proportionate    = true;

    /**
     * Creates a <CODE>StretchIcon</CODE> from an array of bytes.
     *
     * @param imageData an array of pixels in an image format supported by the AWT Toolkit, such as GIF, JPEG, or (as of 1.3) PNG
     *
     * @see ImageIcon#ImageIcon(byte[])
     */
    public StretchIcon(byte[] imageData)
    {
        super(imageData);
    }

    /**
     * Creates a <CODE>StretchIcon</CODE> from an array of bytes with the specified behavior.
     *
     * @param imageData an array of pixels in an image format supported by the AWT Toolkit, such as GIF, JPEG, or (as of 1.3) PNG
     * @param proportionate <code>true</code> to retain the image's aspect ratio, <code>false</code> to allow distortion of the image to
     *            fill the component.
     *
     * @see ImageIcon#ImageIcon(byte[])
     */
    public StretchIcon(byte[] imageData, boolean proportionate)
    {
        super(imageData);
        this.proportionate = proportionate;
    }

    /**
     * Creates a <CODE>StretchIcon</CODE> from an array of bytes.
     *
     * @param imageData an array of pixels in an image format supported by the AWT Toolkit, such as GIF, JPEG, or (as of 1.3) PNG
     * @param description a brief textual description of the image
     *
     * @see ImageIcon#ImageIcon(byte[], java.lang.String)
     */
    public StretchIcon(byte[] imageData, String description)
    {
        super(imageData, description);
    }

    /**
     * Creates a <CODE>StretchIcon</CODE> from an array of bytes with the specified behavior.
     *
     * @see ImageIcon#ImageIcon(byte[])
     * @param imageData an array of pixels in an image format supported by the AWT Toolkit, such as GIF, JPEG, or (as of 1.3) PNG
     * @param description a brief textual description of the image
     * @param proportionate <code>true</code> to retain the image's aspect ratio, <code>false</code> to allow distortion of the image to
     *            fill the component.
     *
     * @see ImageIcon#ImageIcon(byte[], java.lang.String)
     */
    public StretchIcon(byte[] imageData, String description, boolean proportionate)
    {
        super(imageData, description);
        this.proportionate = proportionate;
    }

    /**
     * Creates a <CODE>StretchIcon</CODE> from the image.
     *
     * @param image the image
     *
     * @see ImageIcon#ImageIcon(java.awt.Image)
     */
    public StretchIcon(Image image)
    {
        super(image);
    }

    /**
     * Creates a <CODE>StretchIcon</CODE> from the image with the specified behavior.
     *
     * @param image the image
     * @param proportionate <code>true</code> to retain the image's aspect ratio, <code>false</code> to allow distortion of the image to
     *            fill the component.
     *
     * @see ImageIcon#ImageIcon(java.awt.Image)
     */
    public StretchIcon(Image image, boolean proportionate)
    {
        super(image);
        this.proportionate = proportionate;
    }

    /**
     * Creates a <CODE>StretchIcon</CODE> from the image.
     *
     * @param image the image
     * @param description a brief textual description of the image
     *
     * @see ImageIcon#ImageIcon(java.awt.Image, java.lang.String)
     */
    public StretchIcon(Image image, String description)
    {
        super(image, description);
    }

    /**
     * Creates a <CODE>StretchIcon</CODE> from the image with the specified behavior.
     *
     * @param image the image
     * @param description a brief textual description of the image
     * @param proportionate <code>true</code> to retain the image's aspect ratio, <code>false</code> to allow distortion of the image to
     *            fill the component.
     *
     * @see ImageIcon#ImageIcon(java.awt.Image, java.lang.String)
     */
    public StretchIcon(Image image, String description, boolean proportionate)
    {
        super(image, description);
        this.proportionate = proportionate;
    }

    /**
     * Creates a <CODE>StretchIcon</CODE> from the specified file.
     *
     * @param filename a String specifying a filename or path
     *
     * @see ImageIcon#ImageIcon(java.lang.String)
     */
    public StretchIcon(String filename)
    {
        super(filename);
    }

    /**
     * Creates a <CODE>StretchIcon</CODE> from the specified file with the specified behavior.
     *
     * @param filename a String specifying a filename or path
     * @param proportionate <code>true</code> to retain the image's aspect ratio, <code>false</code> to allow distortion of the image to
     *            fill the component.
     *
     * @see ImageIcon#ImageIcon(java.lang.String)
     */
    public StretchIcon(String filename, boolean proportionate)
    {
        super(filename);
        this.proportionate = proportionate;
    }

    /**
     * Creates a <CODE>StretchIcon</CODE> from the specified file.
     *
     * @param filename a String specifying a filename or path
     * @param description a brief textual description of the image
     *
     * @see ImageIcon#ImageIcon(java.lang.String, java.lang.String)
     */
    public StretchIcon(String filename, String description)
    {
        super(filename, description);
    }

    /**
     * Creates a <CODE>StretchIcon</CODE> from the specified file with the specified behavior.
     *
     * @param filename a String specifying a filename or path
     * @param description a brief textual description of the image
     * @param proportionate <code>true</code> to retain the image's aspect ratio, <code>false</code> to allow distortion of the image to
     *            fill the component.
     *
     * @see ImageIcon#ImageIcon(java.awt.Image, java.lang.String)
     */
    public StretchIcon(String filename, String description, boolean proportionate)
    {
        super(filename, description);
        this.proportionate = proportionate;
    }

    /**
     * Creates a <CODE>StretchIcon</CODE> from the specified URL.
     *
     * @param location the URL for the image
     *
     * @see ImageIcon#ImageIcon(java.net.URL)
     */
    public StretchIcon(URL location)
    {
        super(location);
    }

    /**
     * Creates a <CODE>StretchIcon</CODE> from the specified URL with the specified behavior.
     *
     * @param location the URL for the image
     * @param proportionate <code>true</code> to retain the image's aspect ratio, <code>false</code> to allow distortion of the image to
     *            fill the component.
     *
     * @see ImageIcon#ImageIcon(java.net.URL)
     */
    public StretchIcon(URL location, boolean proportionate)
    {
        super(location);
        this.proportionate = proportionate;
    }

    /**
     * Creates a <CODE>StretchIcon</CODE> from the specified URL.
     *
     * @param location the URL for the image
     * @param description a brief textual description of the image
     *
     * @see ImageIcon#ImageIcon(java.net.URL, java.lang.String)
     */
    public StretchIcon(URL location, String description)
    {
        super(location, description);
    }

    /**
     * Creates a <CODE>StretchIcon</CODE> from the specified URL with the specified behavior.
     *
     * @param location the URL for the image
     * @param description a brief textual description of the image
     * @param proportionate <code>true</code> to retain the image's aspect ratio, <code>false</code> to allow distortion of the image to
     *            fill the component.
     *
     * @see ImageIcon#ImageIcon(java.net.URL, java.lang.String)
     */
    public StretchIcon(URL location, String description, boolean proportionate)
    {
        super(location, description);
        this.proportionate = proportionate;
    }

    /**
     * Paints the icon. The image is reduced or magnified to fit the component to which it is painted.
     * <P>
     * If the proportion has not been specified, or has been specified as <code>true</code>, the aspect ratio of the image will be preserved
     * by padding and centering the image horizontally or vertically. Otherwise the image may be distorted to fill the component it is
     * painted to.
     * <P>
     * If this icon has no image observer,this method uses the <code>c</code> component as the observer.
     *
     * @param c the component to which the Icon is painted. This is used as the observer if this icon has no image observer
     * @param g the graphics context
     * @param x not used.
     * @param y not used.
     *
     * @see ImageIcon#paintIcon(java.awt.Component, java.awt.Graphics, int, int)
     */
    @Override
    public synchronized void paintIcon(Component c, Graphics g, int x, int y)
    {
        Image image = getImage();
        if (image == null)
        {
            return;
        }
        Insets insets = ((Container) c).getInsets();
        x = insets.left;
        y = insets.top;

        int w = c.getWidth() - x - insets.right;
        int h = c.getHeight() - y - insets.bottom;

        if (proportionate)
        {
            int iw = image.getWidth(c);
            int ih = image.getHeight(c);

            if ((iw * h) < (ih * w))
            {
                iw = (h * iw) / ih;
                x += (w - iw) / 2;
                w = iw;
            }
            else
            {
                ih = (w * ih) / iw;
                y += (h - ih) / 2;
                h = ih;
            }
        }
        ImageObserver io = getImageObserver();

        /*
         * Added this code to generate nicer looking results when scaling. - bspkrs
         * BEGIN CHANGES
         */
        BufferedImage bi = new BufferedImage(w, h, BufferedImage.TYPE_4BYTE_ABGR);
        Graphics2D g2d = bi.createGraphics();
        g2d.addRenderingHints(new RenderingHints(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY));
        g2d.drawImage(image, 0, 0, w, h, io == null ? c : io);
        g2d.dispose();
        /*
         * END CHANGES
         */

        g.drawImage(bi, x, y, w, h, io == null ? c : io);
    }

    /**
     * Overridden to return 0. The size of this Icon is determined by the size of the component.
     *
     * @return 0
     */
    @Override
    public int getIconWidth()
    {
        return 0;
    }

    /**
     * Overridden to return 0. The size of this Icon is determined by the size of the component.
     *
     * @return 0
     */
    @Override
    public int getIconHeight()
    {
        return 0;
    }
}