How can I resize an image using Java?

Question

I need to resize PNG, JPEG and GIF files. How can I do this using Java?

Answer 1

You don't need a library to do this. You can do it with Java itself.

Chris Campbell has an excellent and detailed write-up on scaling images - see this article.

Chet Haase and Romain Guy also have a detailed and very informative write-up of image scaling in their book, Filthy Rich Clients.

Answer 2

If, having imagemagick installed on your maschine is an option, I recommend im4java. It is a very thin abstraction layer upon the command line interface, but does its job very well.

Answer 3

Java Advanced Imaging is now open source, and provides the operations you need.

Answer 4

You could try to use GraphicsMagick Image Processing System with im4java as a comand-line interface for Java.

There are a lot of advantages of GraphicsMagick, but one for all:

• GM is used to process billions of files at the world's largest photo sites (e.g. Flickr and Etsy).

Answer 5

Simply use Burkhard's answer but add this line after creating the graphics:

    g.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);

You could also set the value to BICUBIC, it will produce a better quality image but is a more expensive operation. There are other rendering hints you can set but I have found that interpolation produces the most notable effect. Keep in mind if you want to zoom in in a lot, java code most likely will be very slow. I find larger images start to produce lag around 300% zoom even with all rendering hints set to optimize for speed over quality.

Answer 6

It turns out that writing a performant scaler is not trivial. I did it once for an open source project: ImageScaler.

In principle 'java.awt.Image#getScaledInstance(int, int, int)' would do the job as well, but there is a nasty bug with this - refer to my link for details.