How Can I Properly Scale a BufferedImage in Java?

Scaling a BufferedImage: A Comprehensive Guide

Problem Statement

In an attempt to scale a BufferedImage using the Java API, a developer encountered an unsuccessful outcome with the following code:

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

Solution

While the concept of scaling a BufferedImage using Graphics2D.scale() may appear straightforward, it is essential to note that this operation does not actually affect the underlying image data. To achieve true scaling, it is necessary to employ the AffineTransformOp class, which provides enhanced flexibility and interpolation options.

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);

Further Considerations

The code snippet presented exemplifies resampling, a technique that creates a new image with the desired size while maintaining the original image's original aspect ratio. In contrast, cropping, which alters both the size and aspect ratio, is discussed in a separate thread. Additionally, various examples of related concepts are available for further exploration.

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