Scaling a JPEG

[ScottVal]

Hello-
I'm working on a class which will scale-down an image taken from a JPEG file.

I can read the image data into a BufferedImage just fine.

I notice there is an Image method called Image.getScaledInstance(), so I thought, cool, I can use that to scale the image.

However, the method returns an "Image," which is the superclass of BufferedImage, so I can't do anything with the "Image."

The method I want to use to write the BufferedImage back to disk (ImageWriter.write) takes an IIOImage, which I can construct from a BufferedImage. But the fact that I now have an "Image" means that I can't use the constructor.

Thoughts?....
-scott

[pbrockway2]

There is code in org.jdesktop.swingx.graphics.GraphicsUtilities to do this. (if you don't want to reinvent the wheel.)

[ScottVal]

Copying (or using) some one else's code is fine, but I'm wondering why there is this method, which seemingly can't really be used:

In abstract class java.awt.Image:
Image getScaledInstance(int width, int height, int hints)

BufferedImage extends Image.
So, you can use method getScaledInstance on a BufferedImage, but you can't do anything with the result. The result is an Image, not a BufferedImage. I used the debugger to determine that the resulting object is actually of class sun.awt.image.ToolkitImage.

-scott

[ScottVal]

OK--I figured it out.
The trick was to create a BufferedImage of the down-scaled size, then create a graphics context from that BufferedImage, and use drawImage to draw the "Image" object in the graphics context. -scott

[pbrockway2]

OK--I figured it out.

I'm glad you got it sorted.

The trick was...

Yes, exactly. In the code I linked to the (1) create scaled down BI (2) get Graphics context (3) draw into the context steps are illustrated. For example in the createThumbnalFast() method:

//...
BufferedImage temp = createCompatibleImage(image, width, height);
Graphics2D g2 = temp.createGraphics();
g2.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
g2.drawImage(image, 0, 0, temp.getWidth(), temp.getHeight(), null);
g2.dispose();
//...

[OrangeDog]

I would have just used an AffineTransform between BufferedImages.