» CS 145 Lecture 22

CS 145 Lecture 22 – Images

October 31, 2016 by Chris Johnson. Filed under cs145, fall 2016, lectures.

Dear students,

We start today by revisiting memory tracing, but this time in programs with loops. Here we go!

public static String trace1(char c, int n) {
  String s = "";
  for (int i = 0; i < n; ++i) {
    s += c;
  }
  return s;
}

public static void main(String[] args) {
  System.out.println(trace1('*', 6)); 
}

Memory Tracing #2

public static int trace2(int n) {
  int z = 0;
  while (n > 0) {
    ++z;
    n /= 2; // same as n = n / 2
  }
  return z;
}

public static void main(String[] args) {
  System.out.println(trace2(32)); 
}

Memory Tracing #3

public static String trace3(String s, int a, int b) {
  String t = "";
  for (int i = a; i < b; ++i) {
    t += s.charAt(i);
  }
  return t;
}

public static void main(String[] args) {
  System.out.println(trace3("Abraham", 4, 7)); 
}

Memory Tracing #4

public static int trace4(int n) {
  int z = 0;
  while (n > 0) {
    z = z * 10 + n % 10;
    n = n / 10;
  }
  return z;
}

public static void main(String[] args) {
  System.out.println(trace4(24589)); 
}

Then we’ll work on some more image generating programs, hitting upon nested loops and BufferedImage. We’ll write programs that draw…

random noise
a line between two points
a checkerboard pattern
a gradient

Before we meet again, please do the following:

Read sections 2.3, 2.4, 5.1, and 5.2. On a quarter sheet, write down 2-3 questions or observations from your reading.

See you next class!

Sincerely,

P.S. Here’s the code we wrote together…

Noise.java

package lecture1031;

import java.awt.Color;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.Random;
import javax.imageio.ImageIO;

public class Noise {
  public static void main(String[] args) throws IOException {
    BufferedImage image = new BufferedImage(512, 256, BufferedImage.TYPE_BYTE_GRAY);
    Random generator = new Random();

    for (int r = 0; r < image.getHeight(); ++r) {
      for (int c = 0; c < image.getWidth(); ++c) {
        int gray = generator.nextInt(256);
        Color randomColor = new Color(gray, gray, gray);
        image.setRGB(c, r, randomColor.getRGB());
      }
    }

    ImageIO.write(image, "png", new File("/Users/johnch/Desktop/noise.png"));
  }
}

Checkerboard.java

package lecture1031;

import java.awt.Color;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.Random;
import javax.imageio.ImageIO;

public class Checkerboard {
  public static void main(String[] args) throws IOException {
    BufferedImage image = new BufferedImage(256, 256, BufferedImage.TYPE_INT_RGB);

    for (int r = 0; r < image.getHeight(); ++r) {
      for (int c = 0; c < image.getWidth(); ++c) {
//        if (c % 2 == 0 && r % 2 == 0) {
//        if (c % 2 == r % 2) {
          if (c / 32 % 2 == r / 32 % 2) {
          image.setRGB(c, r, Color.ORANGE.darker().darker().darker().darker().brighter().brighter().getRGB());
        } else {
          image.setRGB(c, r, Color.BLACK.getRGB());
        }
      }
    }

    ImageIO.write(image, "png", new File("/Users/johnch/Desktop/check.png"));
  }
}

Gradient.java

package lecture1031;

import java.awt.Color;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.Random;
import javax.imageio.ImageIO;

public class Gradient {
  public static void main(String[] args) throws IOException {
    BufferedImage image = new BufferedImage(1024, 1024, BufferedImage.TYPE_BYTE_GRAY);

    for (int r = 0; r < image.getHeight(); ++r) {
      for (int c = 0; c < image.getWidth(); ++c) {
        int gray = (int) (c / (image.getWidth() - 1.0) * 255);
        image.setRGB(c, r, new Color(gray, gray, gray).getRGB());
      }
    }

    ImageIO.write(image, "png", new File("/Users/johnch/Desktop/gradient.png"));
  }
}