Learning Java

Chapter 18. Working with Images and Other Media

Up to this point, we’ve confined ourselves to working with the high-level drawing commands of the Graphics2D class, using images in a hands-off mode. In this section, we’ll clear up some of the mystery surrounding images and see how they are created and used. The classes in the java.awt.image package handle images and their insides; Figure 18.1 shows the important classes in this package.^[47]

Figure 18-1. The java.awt.image package

First, we’ll return to our discussion of image observers and see how we can get more control over image data as it’s processed asynchronously by GUI components. Then we’ll open the hood and have a look at the inside of a BufferedImage. If you’re interested in creating sophisticated graphics, such as rendered images or video streams, this will teach you about the foundations of image construction in Java.

Implementing an ImageObserver

The architects of Java realized that images might take some time to load over a slow network. Image observers implement the ImageObserver interface. They are effectively nosy neighbors of images that watch as the image data arrives.

An image is simply a rectangle of pixels. A pixel has both a color and a transparency; the transparency specifies how pixels underneath the image show through. For a static image, such as a GIF or JPEG data file, the observer is notified when the entire ...