Writing Image I/O Applications

3.1 Reading and Writing Images

The javax.imageio.ImageIO class provides a set of static convenience methods that perform most simple Image I/O operations.

Reading an image that is in a standard format (GIF, PNG, or JPEG) is simple:

File f = new File("c:\images\myimage.gif");
BufferedImage bi = ImageIO.read(f);

The format of the image will be auto-detected by the API based on the contents of the file. Most image files contain a "magic number" in their first few bytes that identifies the file format. For formats that do not have a magic number, auto-detection may fail and somewhat more sophisticated application code will be needed.

Additional formats may be handled by installing JAR files containing plug-ins; the details are described in the next chapter. Once a plug-in has been installed, a new format will be understood automatically without any changes to the application code.

The set of formats available for reading can be obtained by calling ImageIO.getReaderFormatNames. This will return an array of Strings containing the names of the available formats, such as "gif" and "png."

Writing an image in a supported format is equally simple:

BufferedImage bi;
File f = new File("c:\images\myimage.png");
ImageIO.write(im, "png", f);

The list of supported formats may be obtained by calling ImageIO.getWriterFormatNames.