Presents your 
JAVA E-NEWSLETTER for September 12, 2002

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EXPAND JAVA IMAGE ABILITIES WITH JAI

Java Image abilities are constantly growing, but writing one to disk or
returning it as a PNG or JPEG is still black magic. The solution is to
use the Java Advanced Imaging (JAI) API. JAI is available as a download
from Sun's Java Web site, and it's included in JDK 1.4 in the 
javax.imageio package.
http://java.sun.com/

An automatic JAI installation .exe file is available for Windows, but
not for UNIX and Linux. Although JAI can run in a pure-java mode, there are
also native libraries for Windows, Linux, and UNIX, which increase the speed.

The following example was installed on Apple's OS X, so we opted for the
pure-java mode. To install the JAI, you'll need one of the jai tar.gz
files. Move the three important jar files, mlibwrapper_jai.jar,
jai_codec.jar, and jai_core.jar, into your classpath. We recommend 
putting them in your JDK's jre/lib/ext directory.

The JAI is quite an odd system for Java. Rather than having lots of
methods to learn, there's just one top-level class named JAI and a handful of
helper methods. The first argument to these methods is an operation
name, so the code will look like this:

source = JAI.create("fileload", .. );
JAI.create("extrema", src, ...);
JAI.create("histogram", src, ...);

While this system makes it very easy to plug in your own or third-party
functionalities, it also loosens the typing and makes it more difficult
to develop under.

Turning an AWT Image into a PNG file requires the following snippets of
code.

import java.awt.Image;
import java.awt.image.renderable.ParameterBlock;

import javax.media.jai.JAI;
import javax.media.jai.PlanarImage;

.....

    Image img = ....
    OutputStream out = ....
    ParameterBlock pb = new ParameterBlock().add(img);
    PlanarImage src = (PlanarImage) JAI.create("awtImage", pb);
    JAI.create("encode", src, out, "PNG", null);

The above example shows the two ways in which arguments may be passed
into the create method. The newer way is to use a ParameterBlock containing
all the arguments. We do this for the awtImage operation. The older way
is to use an overloaded method. This is now deprecated, but for the
example, we do this for the encode operation.

The code above will encode an Image to a PNG and write it to the
OutputStream. To get further into the JAI, we strongly recommend 
reading the tutorial.

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