Main.java

package asmt2;

import java.awt.*;
import java.awt.image.*;
import javax.imageio.ImageIO;
import java.io.*;

public class Main {
  // define the three drawing modes
  private static final int EDGE_DETECTOR = 0;
  private static final int GRAYSCALE = 1;
  private static final int EDGE_ENHANCEMENT = 2;
  private static final int COLOR_OUTLINES = 3;

  public static void main(String[] args) {
    if (args.length >= 3) {
      BufferedImage img = null, edges = null, result = null;

      int mode = Integer.parseInt(args[2]);

      try {
        img = ImageIO.read(new File(args[0]));
        edges = ImageIO.read(new File(args[0]));
        result = ImageIO.read(new File(args[0]));
      } catch (IOException e) {
        System.out.println("Could not load file.");
        System.exit(1);
      }
      for (int x = 0; x < img.getWidth(); x++) {
        for (int y = 0; y < img.getHeight(); y++) {
          int gradX, gradY;
          Color left, right, up, down;
          if (x == 0) {
            // if we are on the left edge
            left = new Color(img.getRGB(x, y));
            right =  new Color(img.getRGB(x+1, y));
          } else if (x == img.getWidth() - 1) {
            // if we are on the right edge
            left = new Color(img.getRGB(x-1, y));
            right = new Color(img.getRGB(x, y));
          } else {
            // if we are in the middle of the image
            left = new Color(img.getRGB(x-1, y));
            right = new Color(img.getRGB(x+1, y));
          }
          // sum up the red, green, and blue horizontal components of the gradient
          gradX = Math.abs(right.getRed() - left.getRed()) + Math.abs(right.getGreen() - left.getGreen()) + Math.abs(right.getBlue() - left.getBlue());
          if (y == 0) {
            // if we are on the top edge
            up = new Color(img.getRGB(x, y));
            down =  new Color(img.getRGB(x, y+1));
          } else if (y == img.getHeight() - 1) {
            // if we are on the bottom edge
            up = new Color(img.getRGB(x, y-1));
            down = new Color(img.getRGB(x, y));
          } else {
            // if we are the middle of the image
            up = new Color(img.getRGB(x, y-1));
            down = new Color(img.getRGB(x, y+1));
          }
          // sum up the red, green, and blue vertical components of the gradient
          gradY = Math.abs(down.getRed() - up.getRed()) + Math.abs(down.getGreen() - up.getGreen()) + Math.abs(down.getBlue() - up.getBlue());

          // sum up the horizontal and vertical components of the gradient, with a maximum value of 1530
          int grad = gradX + gradY;

          // Map the total gradient onto a logistic curve from 0 to 255.
          // A logistic curve is like a smoothed out step function, so that brighter values get brighter and darker values get darker.
          int brightness = (int)(255.0 * (1.0 / (1.0 + Math.exp(- (( ((float)grad) * (12.0 / 1530.0) ) - 3.0)))));
          switch (mode) {
            case EDGE_DETECTOR:
              // Set a pixel to white if the gradient is above a threshold and to black if otherwise.
              if (grad > 200) {
                result.setRGB(x, y, 0xffffffff);
              } else {
                result.setRGB(x, y, 0x00000000);
              }
            break;
            case GRAYSCALE:
              // Simply set the brightness of a pixel to the gradient there.
              result.setRGB(x, y, (new Color(brightness, brightness, brightness)).getRGB());
            break;
            case EDGE_ENHANCEMENT:
              Color edgeColor = (new Color(brightness, brightness, brightness));

              edges.setRGB(x, y, edgeColor.getRGB());

              Color resultColor = new Color(result.getRGB(x, y));

              // Brighten the image where edges are found.
              result.setRGB(x, y, (new Color(Math.min(255, resultColor.getRed() + edgeColor.getRed()), Math.min(255, resultColor.getGreen() + edgeColor.getGreen()), Math.min(255, resultColor.getBlue() + edgeColor.getBlue()))).getRGB());
            break;
            case COLOR_OUTLINES:
              edges.setRGB(x, y, (new Color(brightness, brightness, brightness)).getRGB());

              // Superimpose red, green, and blue versions of the edges at offsets from their original positions.
              if (x + 2 < result.getWidth() && y + 3 < result.getHeight()) {
                result.setRGB(x + 2, y + 3, result.getRGB(x + 2, y + 3) + Math.min(edges.getRGB(x, y) & 0x00ff0000, (0x00ff0000 - (result.getRGB(x + 2, y + 3) & 0x00ff0000))));
              }
              if (x - 3 > 0 && y + 2 < result.getHeight()) {
                result.setRGB(x - 3, y + 2, result.getRGB(x - 3, y + 2) + Math.min(edges.getRGB(x, y) & 0x0000ff00, (0x0000ff00 - (result.getRGB(x - 3, y + 2) & 0x0000ff00))));
              }
              if (y - 3 > 0) {
                result.setRGB(x, y - 3, result.getRGB(x, y - 3) + Math.min(edges.getRGB(x, y) & 0x000000ff, (0x000000ff - (result.getRGB(x, y - 3) & 0x000000ff))));
              }
            break;
          }
        }
      }

      try {
        ImageIO.write(result, "jpg", new File(args[1]));
      } catch (IOException e) {
        System.out.println("Could not save file.");
        System.exit(1);
      }
    } else {
      System.out.println("Please provide an input file, an output file, and a mode (0, 1, 2, or 3).");
      System.exit(1);
    }
  }
}