Learning Java, 4th Edition

Saving Image Data

We’ve spent a lot of time talking about loading images from files and generating and transforming image data, but nothing about saving it. First, let’s remember that saving an image to a file such as a JPG or GIF really implies doing two things: encoding it (highly compressing the data in a way optimized for the type of image) and then writing it to a file, possibly with various metadata. As we mentioned earlier, the core AWT does not provide tools for encoding image data, only decoding it. By contrast, the ImageIO framework has the capability of writing images in any format that it can read.

Writing a BufferedImage is simply a matter of calling the static ImageIO write() method:

    File outFile = new File("/tmp/myImage.png");
    ImageIO.write( bufferedImage , "png", outFile );

The second argument is a string identifier that names the image type. You can get the list of supported formats by calling ImageIO.getWriterFormatNames(). We should note that the actual type of the image argument is something called RenderedImage, but BufferedImage implements that interface.

You can get more control over the encoding (for example, JPG quality settings) by getting an ImageWriter for the output format and using ImageWriteParams. The process is similar to that in the reader progress listener snippet from the section ImageIO.