How to get scaled instance of a bufferedImage

问题:

I wanted to get scaled instance of a buffered image and I did:

public void analyzePosition(BufferedImage img, int x, int y){   
     img =  (BufferedImage) img.getScaledInstance(getWidth(), getHeight(), Image.SCALE_SMOOTH);
....
}

but I do get an exception:

Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: sun.awt.image.ToolkitImage cannot be cast to java.awt.image.BufferedImage
    at ImagePanel.analyzePosition(ImagePanel.java:43)

I wanted then to cast to ToolkitImage then use the method getBufferedImage I read about in other articles. The problem is there is no class such as sun.awt.image.ToolkitImage I cannot cast to it because Eclipse does not even see this class. I use Java 1.7 and jre1.7.

回答1:

You can create a new image, a BufferedImage with the TookitImage.

Image toolkitImage = img.getScaledInstance(getWidth(), getHeight(), 
      Image.SCALE_SMOOTH);
int width = toolkitImage.getWidth(null);
int height = toolkitImage.getHeight(null);

// width and height are of the toolkit image
BufferedImage newImage = new BufferedImage(width, height, 
      BufferedImage.TYPE_INT_ARGB);
Graphics g = newImage.getGraphics();
g.drawImage(toolkitImage, 0, 0, null);
g.dispose();

// now use your new BufferedImage

回答2:

BufferedImage#getScaledInstance is actually inherited from java.awt.Image and only guarantees that it will return an Image so I would say it's not a good idea to try and assume the underlying return type in this case.

getScaledInstance is, also, not normally the fastest or best quality method

To scale a BufferedImage itself, you have a number of different options, but most simply take the original and repaint it to another image, applying some kind of scaling in process.

For example:

• Scale the ImageIcon automatically to label size
• Position Image in any Screen Resolution
• how to make image stretchable in swing?

For more details about getScaledInstance, have a read of The Perils of Image.getScaledInstance()