My code currently projects a radon transform of the image that I have selected, but I would like to know how to create the back projection of the inverse radon transform and reconstruct the image. Here is my code for the forward radon transform:
package radon;
 
import gui.ClosableJFrame;
import j2d.ImageUtils;
 
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.File;
 
public class InverseRadonTransform {
    public static void main(String[] args) throws InterruptedException {
        //File f = Futil.getReadFile("select a radon image");
        File f = new File("/Users/StephCruz/School/biomed. vis./Midterm/peppers.JPEG");
        System.out.println(f);
        BufferedImage frtImage = ImageUtils.getBufferedImage(
                ImageUtils.getImage(f));
        int w = frtImage.getWidth();
        int h = frtImage.getHeight();
        double delta_theta = Math.PI / w;
        ClosableJFrame cf = new ClosableJFrame();
        Container c = cf.getContentPane();
        c.setLayout(new GridLayout(1, 3));
        BufferedImage outputImage = ImageUtils.getBufferedImage(w,h);
        RotatedImagePanel frtPanel = new RotatedImagePanel(frtImage);
        RotatedImagePanel rotatedImagePanel = new RotatedImagePanel(frtImage);
        OutputImagePanel outputImagePanel = new OutputImagePanel(outputImage);
 
        cf.addComponent(frtPanel);
        cf.addComponent(rotatedImagePanel);
        cf.addComponent(outputImagePanel);
        cf.setSize(3 * w, h);
        cf.setVisible(true);
        for (int colIndex =0; colIndex < w; colIndex++) {
 
            //rti=radon transform image
            //frt = forward radon transform
            //bp=back projection
 
            outputImagePanel.setBackProj(frtPanel.getCol(colIndex));
 
            double theta = delta_theta* colIndex;
 
            rotatedImagePanel.setRotation(theta);
 
            //System.out.println("x="+x+" w="+w);
 
            rotatedImagePanel.repaint();
            outputImagePanel.repaint();
            //Thread.sleep(10);
        }
        //rotatedImagePanel.repaint();
        //outputImagePanel.repaint();
        //ImageUtils.saveAsJpeg(outputImagePanel.getOutputImage(),
         //       Futil.getWriteFile("select output image file name"));
    }
 
}

Thanks for the help!