Prelab 10 : Coordinates in Pictures

Reading

• Chapter 3 and from Learning Computing With Robots
• Wikipedia entry on Chroma key

Addressing pixels in an image

1. Describe the difference between the three different loops below. That is, what does each do? How many times is Hello printed in each case? for i in range(4): print "Hello" while timeRemaining(4): print "Hello" while True: print "Hello"
2. Consider this code and fill in the blanks below:
   

   for x in range(0,1000):
     print x # First command
   print x #Second command
   

   
   
   1. The number of times the first print command is executed: ...........
      
   2. The number of times the second print command is executed: ..........
      
3. What does the following code do? What will the resulting image (myPic look like? MAX = 255 W = 100 H = 100 # Create the blank image myPic = makePicture(W, H) # Fill in each pixel with x+y shade of gray for x in range(W): for y in range(H): grayVal = (x+y)%(MAX+1) setPixel(myPic, x, y, makeColor(grayVal, grayVal, grayVal))

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