Need help on transforming a bufferedimage back to an image

Question

Hi,
for a project in school, I need to read in a .jpeg file, transform it to a bufferedimage, getting the pixels. Then I make a new bufferedimage and all the RGB values that are higher then a certain (changeable) contrast value are made white, the other black (so basicly i transform an image to black and white) (with getRGB from colorimage and setRGB to the new bufferedimage)
But I have trouble to transform the black and white bufferedimage to an image for viewing the image...
The code for that part is like this:
public void beeldWeergeven(){
     for (int j=0;j>height;j++){
          for (int i=0;i<width;i++){
               waarde = zwartwitmatrix[j][i]*255;
               imagezw.setRGB(i,j,waarde);
     Image zwimage = toImage(imagezw);
     zwimage = null;{
     JFrame frame = new JFrame();
JLabel label = new JLabel(new ImageIcon(zwimage));
frame.getContentPane().add(label, BorderLayout.CENTER);
frame.pack();
frame.setVisible(true);
public static Image toImage(BufferedImage bufferedImage) {
return Toolkit.getDefaultToolkit().createImage(bufferedImage.getSource());
When I compile, I always get a nullpointerexception
I'm not that good at writing java, so if anyone could lend me a hand on this :)

Answer 1

For the moment (guess you know there are other ways to Black and White anyway):
for (int j=0;j>height;j++)
should be
for (int j=0;j<height;j++)
possibly??