CS 101

Fancy Filters

Plan for Today

  • Last time, we learned about if statements, a way to conditionally apply operations.
  • Now, we're going to experiment with if statements by creating a green screen filter.

Green Screen Example

Green Screen

  • Works by replacing all the pixels of a certain color in one image with another image
    • Color depends on the original image
  • Idea: if a pixel is "close" in color to our target color, replace it with the corresponding pixel in the other image

Green Screen Continued

  • How do we replace a pixel with another?
  • Recall:
    • if(pixel1.isSimilarTo(RED, GREEN, BLUE, NUMBER))
    • The RED, GREEN, and BLUE values represent the target color
    • NUMBER is the "tolerance": bigger number be true more often. Should be between 0 and 255
    • No need to use an inequality operator; that line of code just gives us a true or false directly
yosemite.jpg paris.jpg

Writing Green Screen


"Faded" Green Screen


Idea: instead of using the original pixel values, can blend them with background

Talk with a partner on how to modify the green screen code to achieve this effect

Writing Faded Green Screen


Green Screen: Multiple Passes

Write code to replace the red stop sign with leaves, and the blue sky with yosemite



  • Midterm is in STLC 115 in two weeks!
    • Email Shreya and me your OAE accommodations please
  • Moving back to Canvas


Today, we learned more complicated methods for editing images, seeing the power of if statements and for loops. Next time, we'll move away from images and manipulate other kinds of data.