Compute the image processing

Hi,

Question 1:

I have some questions here first I need some suggestion - I cannot find what went wrong with my code here to find the averaging of the image (grey image) also, How do i compute an average with a colour images one?

Question 2:
I need to compute the subtraction of the image using hte g(x,y) = |f1(x,y) - f2(x,y) How do i change the code so it will implement the subtraction by inputing two images in the Subtraction program?

Question 3:
I need to find the Brightness by adding the constant to all value which is
g'(x,y) = g(x,y) + k. Say k = 50.

Question 4:
Finding the contrast of the image by scale all value by constant of
g'(x,y) = g(x,y) * k. Say k = 1.5


Thanks
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import java.io.*;
import java.awt.image.*;
import java.awt.color.ColorSpace;
import javax.swing.*;
import com.pearsoneduc.ip.io.*;
import com.pearsoneduc.ip.gui.*;

public class AverageXImage extends JFrame {

private BufferedImage sourceImage;
private ImageView[] views;


public AverageXImage(String imageFile) throws IOException, ImageDecoderException {

super("xAverage: " + imageFile);
readImage(imageFile);

views = new ImageView[2];
views[0] = new ImageView(sourceImage);

Error found in this line---- views[1]=newImageView(average(sourceImage);

JTabbedPane tabbedPane = new JTabbedPane();
tabbedPane.add(new JScrollPane(views[0]), "input");
tabbedPane.add(new JScrollPane(views[1]), "xAverage");

getContentPane().add(tabbedPane);
addWindowListener(new WindowMonitor());
}
public void readImage(String filename)
throws IOException, ImageDecoderException {
ImageDecoder input = ImageFile.createImageDecoder(filename);
sourceImage = input.decodeAsBufferedImage();
if (sourceImage.getType() != BufferedImage.TYPE_BYTE_GRAY) {

System.err.println("Converting colour image to greyscale image...");
ColorConvertOp op = new ColorConvertOp(
ColorSpace.getInstance(ColorSpace.CS_GRAY), null);
BufferedImage greyImage = op.filter(sourceImage, null);
sourceImage = greyImage;
}
}

public BufferedImage average(BufferedImage[] imgArray) {
//instantiate a new image object

int n = imgArray.length;
int w = n*imgArray[0].getWidth();
int h = n*imgArray[0].getHeight();

BufferedImage AvgImage = new BufferedImage(w, h, BufferedImage.TYPE_BYTE_GRAY);

for (int y = 0; y < h; ++y)
for (int x = 0; x < w; ++x){
//here is to save the original image
float sum = 0.0f;
for (int i = 0; i < n; ++i)
sum += imgArray[i].getRaster().getSample(x, y, 0);
AvgImage.getRaster().setSample(x, y, 0, Math.round(sum/n));
}
return AvgImage;
}
public static void main(String[] argv) {
if (argv.length > 0) {

try {
JFrame frame = new AverageXImage(argv[0]);

frame.pack();
frame.setVisible(true);
} catch (Exception e) {
System.err.println(e);
System.exit(0);
}
} else {
System.err.println("usage: java enlarge <imagefile> ");
System.exit(1);
}
}
}