gistfile1.java

package asmt2;

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

public class Main {
  public static void main(String[] args) {
    if (args.length >= 2) {
      BufferedImage img = null;
      try {
        img = ImageIO.read(new File(args[0]));
      } catch (IOException e) {
        System.out.println("Could not load file.");
        System.exit(1);
      }
      BufferedImage edges = new BufferedImage(img.getWidth(), img.getHeight(), BufferedImage.TYPE_INT_ARGB);
      for (int x = 0; x < edges.getWidth(); x++) {
        for (int y = 0; y < img.getHeight(); y++) {
          edges.setRGB(x, y, 0xff000000);
        }
      }
      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) {
            // left edge
            left = new Color(img.getRGB(x, y));
            right =  new Color(img.getRGB(x+1, y));
          } else if (x == img.getWidth() - 1) {
            // right edge
            left = new Color(img.getRGB(x-1, y));
            right = new Color(img.getRGB(x, y));
          } else {
            left = new Color(img.getRGB(x-1, y));
            right = new Color(img.getRGB(x+1, y));
          }
          gradX = Math.abs(right.getRed() - left.getRed()) + Math.abs(right.getGreen() - left.getGreen()) + Math.abs(right.getBlue() - left.getBlue());
          if (y == 0) {
            // top edge
            up = new Color(img.getRGB(x, y));
            down =  new Color(img.getRGB(x, y+1));
          } else if (y == img.getHeight() - 1) {
            // bottom edge
            up = new Color(img.getRGB(x, y-1));
            down = new Color(img.getRGB(x, y));
          } else {
            up = new Color(img.getRGB(x, y-1));
            down = new Color(img.getRGB(x, y+1));
          }
          gradY = Math.abs(down.getRed() - up.getRed()) + Math.abs(down.getGreen() - up.getGreen()) + Math.abs(down.getBlue() - up.getBlue());

          int grad = gradX + gradY;
          if (grad > 300) {
            edges.setRGB(x, y, 0xffffffff);
          } else {
            edges.setRGB(x, y, 0x00000000);
          }
          //edges.setRGB(x, y, (new Color(grad, grad, grad)).getRGB());
        }
      }

      try {
        ImageIO.write(edges, "jpg", new File(args[1]));
      } catch (IOException e) {
        System.out.println("Could not save file.");
        System.exit(1);
      }
    } else {
      System.out.println("Please provide input and output files.");
      System.exit(1);
    }
  }
}