teaching machines

CS 145 Lecture 21 – Image Manipulation

October 20, 2014 by Chris Johnson. Filed under cs145, fall 2014, lectures.

Agenda

• what ?s
• working with images
• program this

Program This

Grayscale images are two-dimensional grids of pixels. Each pixel is represented as an int in [0, 255], with 0 being black and 255 being white.

Imagine a grayscale image that can be generated with an algorithm. Many patterns and shapes can be produced by algorithms. Write pseudocode to generate this image.

Code

Image.java

package lecture1020;

import java.util.Random;

public class Image {
  public static void main(String[] args) {
    int width = 128;
    int height = 256;
    
    System.out.println("P2");
    System.out.println(width + " " + height);
    System.out.println(255);
    
    makePacman(width, height);
  }
  
  public static void makeStatic(int width, int height) {
    Random g = new Random();
    
    for (int r = 0; r < height; ++r) {
      for (int c = 0; c < width; ++c) {
        System.out.println(g.nextInt(256));
      }
    }
  }
  
  public static void makeStripes(int width, int height) {
    for (int r = 0; r < height; ++r) {
      for (int c = 0; c < width; ++c) {
        if (c % 10 <= 3) {
          System.out.println(0);
        } else {
          System.out.println(255);
        }
      }
    }
  }
  
  public static void makeDiagonals(int width, int height) {
    for (int r = 0; r < height; ++r) {
      for (int c = 0; c < width; ++c) {
        if (c % 10 <= 3 && r != 0 && c / r == 1) {
          System.out.println(0);
        } else {
          System.out.println(255);
        }
      }
    }
  }
  
  public static void makePacman(int width, int height) {
    int rCenter = height / 2;
    int cCenter = width / 2;
    
    for (int r = 0; r < height; ++r) {
      int diffR = r - rCenter;
      for (int c = 0; c < width; ++c) {
        int diffC = c - cCenter;
        double distance = Math.hypot(diffR, diffC);
        if (distance < 14) {
          System.out.println(0);
        } else {
          System.out.println(255);
        }
      }
    }
  }
}

Haiku