CS 40 - Lecture 15

Cay S. Horstmann

Lecture 14 Recap

• Attack pathways: Attacker connects to your computer via network, causes you to execute a program, or causes your computer to execute a script
• Attackers: Thieves (of your money or your computer resources), spammers, vandals
• Remedies: Run antivirus/firewall, install patches, don't run as admin, consider Linux/Mac OS

Making a Sunset

• Want more red
• How about red = red * 1.5
• Fails for red values near 255
• How about leaving red unchanged and reducing blue, green?

Lab 1

• Start Greenfoot
• Make a subclass MyPicture3 of Picture
• Write a sunset method (similar to decreaseRed in MyPicture1)
• Change code so that red is not changed, blue and green are multiplied with a factor of your choice (should be between 0.1 and 0.9)
• Compile. Fix any errors and recompile if necessary
• Right-click on MyPicture3, choose new MyPicture3(), drag into world on left
• Right-click on image, choose pick from Picture methods
• Pick an image. (The Road works fine, but you may want to google for a tropical island photo instead.)
• Select sunset()
• Submit screen capture to ActiveLecture.org (Click on add capture, then bring Greenfoot to the front and use the camera icon)

Bored?

• Try out the idea that Mark Guzdial had first

  double red = pix.getRed();
  red = red * 1.3;
  if (red > 255) red = 255;
  pix.setRed(red);

• What happens?
• (If you aren't squeamish) What happens if you don't have the if (red > 255) red = 255; statement?

Creating a Negative

• Turn black to white, white to black
• 0 to 255, 255 to 0
• x to 255 - x
• Do it for the red, green, blue values separately

Lab 2

• Make class MyPicture4.java
• Add negative method
• Copy basic loop structure from prior exercise or MyPicture1.java
• Get red, blue, green value from pixel: double red = pix.getRed(); etc.
• Compute the new red, green, blue values
• Set them
• Compile. Fix errors. Compile. Fix Errors....
• Try it out with a picture of your choice.
• What happens when you invoke negative twice?
• Submit your solution at the end of class

Bored?

• It is a teensy bit inefficient to call setRed, setGreen, setBlue separately.
• Sophisticated and object-oriented approach:
  • Make a Color object with the right colors

    Color inverse = new Color(red, green, blue);

  • Call setColor:

    pix.setColor(inverse);

• Try it out!

Grayscale

Grayscale

• Change all color values to shade of gray

  Color grayColor = new Color(intensity, intensity, intensity)
  pix.setColor(grayColor);

• Simple version: Intensity is average of red, green, blue

  double intensity = 0.333 * red + 0.333 * green 
     + 0.333 * blue;

• More accurate:

  double intensity = 0.299 * red + 0.587 * green 
     + 0.114 * blue;

Lab 3

• Add the method grayscale to the MyPicture4 class.
• Compile. Fix errors. Compile. Fix Errors....
• Get a picture of the Eiffel tower (or any picture of your choice other than The Road) and do the grayscale e transformation.
• Then do the negative transformation.
• Do them in opposite order. Is there a visible difference?

Bored?

• Compare the simple and accurate methods. Make two methods, simpleGrayscale and accurateGrayscale.
• Is there a difference in practice? If so, which looks nicer?

Reminders

• Submit your labs (MyPicture3.java, MyPicture4.java) to eCampus
• Homework 6 due next Tuesday.
• Intermediate project report due Apr. 17