mount_hood.jpg

graduates.jpg

goalkeeper.jpg

student1.jpg

student2.jpg

green_screen.jpg

scooter.jpg

logo.jpg

cat.jpg

14.3. Combining Pictures

A common use of color replacement technology is “green scren” background replacement. An actor performs in front of a green wall or a Zoom meeting participant sits in front of a green sheet. A computer algorithm them looks for green pixels and replaces them with pixels from some other image. The result is that the person looks like they are in some other location. (Unless of course they have a green shirt on, in which case it will look like their disembodied head is floating in the background.)

We are going to put the woman shown below into the beach scene:

First up, we need to have an isGreen function to identify which pixels are part of the green background. It will be very similar to the isRed from the last page, only we want to verify that the green is greater than the red or blue values.

Write code to return True if the green value is 20 or more greater than both the red and blue values. Otherwise, return False

from image import * def isGreen(r, g, b): #Write your logic here # Main part of program # These three should be considered green print( isGreen(59, 165, 119) ) print( isGreen(47, 142, 102) ) print( isGreen(60, 220, 125) ) # These should not be considered green print( isGreen(200, 200, 200) ) # gray print( isGreen(180, 180, 0) ) # dark yellow print( isGreen(200, 0, 200) ) # aqua ===== from unittest.gui import TestCaseGui class myTests(TestCaseGui): def testOne(self): self.assertEqual(isGreen(59, 165, 144), True, "Testing 59, 165, 144.") self.assertEqual(isGreen(47, 142, 102), True, "Testing 47, 142, 102.") self.assertEqual(isGreen(190, 220, 125), True, "Testing 190, 220, 125.") self.assertEqual(isGreen(200, 200, 200), False, "Testing 200, 200, 200.") self.assertEqual(isGreen(180, 180, 0), False, "Testing 180, 180, 0.") self.assertEqual(isGreen(200, 0, 200), False, "Testing 200, 0, 200.") myTests().main()

Once you get that working, you can bopy and paste it into the program below. It will load the two pictures, with the woman stored as img1 and the beach as img2. It the goes through each pixel in img1 and asks isGreen about it. If so, that pixel gets replaced with the pixel from img2 that is at the same x, y.

from image import * # PUT YOUR isGreen CODE HERE # Main program # CREATE THE IMAGES img1 = Image("green_screen.jpg") img2 = Image("beach.jpg") # LOOP THROUGH ALL THE PIXELS IN IMG1 for x in range(img1.getWidth()): for y in range(img1.getHeight()): p1 = img1.getPixel(x, y) r1 = p1.getRed() g1 = p1.getGreen() b1 = p1.getBlue() # CHECK IF THE PIXEL IS GREEN if isGreen(r1, g1, b1): # GET THE CORESPONDING PIXEL FROM img2 p2 = img2.getPixel(x, y) # USE THAT INSTEAD in img1 img1.setPixel(x, y, p2) # SHOW THE CHANGED IMAGE win = ImageWin(img1.getWidth(), img1.getHeight()) img1.draw(win)

Which of these recipes will result in just the faces being in color and the outer parts of the image being in black and white?

• y < 110 and y > 10 and x > 70 and x < 200
• That will select pixels in the middle of the screen (y from 10-110 and x from 70-200). We want the opposite.
• (y > 110 or y < 10) and (x < 70 or x > 200)
• That requires both the x and y to be outside the center area. It will make a "cross" of color.
• y > 110 and y < 10 and x < 70 and x > 200
• How can the y be > 110 and also be < 10? There will be no pixels that meet the criteria to be changed.
• y > 110 or y < 10 or x < 70 or x > 200
• Correct

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