Why Doesn\'t Graphics2D.scale() Resize a BufferedImage, and How Can I Effectively Scale It?

How to Scale a BufferedImage Effectively

Question:

In the following code, an attempt to scale a BufferedImage using Graphics2D.scale() is not successful. What could be the reason for this?

BufferedImage image = MatrixToImageWriter.getBufferedImage(encoded);
Graphics2D grph = image.createGraphics();
grph.scale(2.0, 2.0);
grph.dispose();

Answer:

The Graphics2D.scale() method simply applies a scaling transformation to the current graphics context without actually modifying the BufferedImage. To resize the image itself, a different approach should be taken.

Solution Using AffineTransformOp:

One way to scale a BufferedImage effectively is to use an AffineTransformOp. This allows for more control over the scaling process, including the interpolation type. Here's an example:

BufferedImage before = getBufferedImage(encoded);
int w = before.getWidth();
int h = before.getHeight();
BufferedImage after = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
AffineTransform at = new AffineTransform();
at.scale(2.0, 2.0);
AffineTransformOp scaleOp = 
   new AffineTransformOp(at, AffineTransformOp.TYPE_BILINEAR);
after = scaleOp.filter(before, after);

In this code:

• A new BufferedImage (after) is created with the same width and height as the original.
• An AffineTransform is created to scale the image by 2x.
• An AffineTransformOp is created using the transform and a specific interpolation type (TYPE_BILINEAR).
• The filter() method is used to apply the scaling operation to the original image, creating the scaled after image.

Note:

• This approach uses resampling to scale the image, rather than cropping.
• For more information on image scaling and cropping, refer to related resources and examples.

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