Question:
How do I transform the color space of an image?from its original space to grayscale, for instance?

Answer:
The ColorSpace class is defined in the java.awt.color package.It encapsulates the transformations that convert pixel values from onecolor space to another, such as RGB to Photo YCC. ColorSpacecontains a factory method, called getInstance() that will create oneof a set of predefined ColorSpace instances represented by constants,such as CS_sRGB and CS_GRAY. A ColorSpace can be used to define atransformation with the ColorConvertOp class defined in thejava.awt.image package.

An actual conversion can be performed byusing the filter() method, which will convert a source image to adestination image. The first argument to the method is the sourceimage and the second argument is the destination image. Both of thesemust be stored as instances of BufferedImage.

The second argument isoptional and if set to null, the method will create and return a newBufferedImage containing the converted image. To get aBufferedImage’s ColorSpace, you must first get its ColorModel withgetColorModel(). ColorModel is also defined in java.awt.image.Different from a ColorSpace, a ColorModel translates a pixel value toits components, such as RGB and alpha values.

You can fetch theColorSpace from the ColorModel with getColorSpace(). The followingexample program ties together these elements to convert an image fromits source color space to a gray scale color space and displays bothimages in two different frames.

import java.awt.*;import java.awt.color.*;import java.awt.event.*;import java.awt.image.*;import javax.swing.*;public class ColorConvert {  public static class ImageCanvas extends Canvas {    Image image;    public ImageCanvas(Image image) {      this.image = image;    }    public void paint(Graphics g) {      update(g);    }    public void update(Graphics g) {      g.drawImage(image, 0, 0, this);    }  }  public static void main(String[] args) {    ImageIcon icon;    BufferedImage convertedImage, sourceImage;    ColorSpace colorSpace;    ColorConvertOp conversionOp;    Graphics graphics;    final Frame originalFrame, convertedFrame;    WindowAdapter exitListener;    int width, height;    if(args.length < 1) {      System.err.println("Usage: ColorConvert imagefile");      return;    }    icon = new ImageIcon(args[0]);    width  = icon.getIconWidth();    height = icon.getIconHeight();    sourceImage =       new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);    graphics = sourceImage.getGraphics();    graphics.drawImage(icon.getImage(), 0, 0, null);    colorSpace     = ColorSpace.getInstance(ColorSpace.CS_GRAY);    conversionOp   = new ColorConvertOp(colorSpace, null);    convertedImage = conversionOp.filter(sourceImage, null);    originalFrame = new Frame("Source Image");    originalFrame.add(new ImageCanvas(sourceImage), BorderLayout.CENTER);    convertedFrame = new Frame("Converted Image");    convertedFrame.add(new ImageCanvas(convertedImage), BorderLayout.CENTER);    exitListener = new WindowAdapter() {      public void windowClosing(WindowEvent e) {        originalFrame.setVisible(false);        convertedFrame.setVisible(false);        originalFrame.dispose();        convertedFrame.dispose();        System.exit(0);      }    };    originalFrame.addWindowListener(exitListener);    convertedFrame.addWindowListener(exitListener);    originalFrame.setSize(width, height);    convertedFrame.setSize(width, height);    originalFrame.setVisible(true);    convertedFrame.setVisible(true);  }}