Chapter 11 Exercises¶

Below is a selection of images that you can use in the programs in this section.

beach.jpg	baby.jpg	vangogh.jpg	swan.jpg

puppy.jpg	kitten.jpg	girl.jpg	motorcycle.jpg

gal1.jpg	guy1.jpg	gal2.jpg

1. Fix 6 syntax errors in the code below so that it correctly sets the red in all pixels to 0.

   # Use the image library from PIL import # Connect to an image file img = Image.open('gal2.jpg' # Load the pixels pixels = img.load # Loop through the pixels for x in range(img.size[0]): for y in range(img.size[1]): r, g, b = pixels[] # Set the red to 0 pixels[x, y] = , g, b # Show the result img.show

2. The code below makes the image have a green-blue tint. Change 1 thing in order to make it have a red tint instead.

   # Use the image library from PIL import Image # Connect to the image img = Image.open('puppy.jpg') # Load the pixels pixels = img.load() # Loop through the pixels for x in range(img.size[0]): for y in range(img.size[1]): r, g, b = pixels[x, y] # Set the color pixels[x, y] = 0, g, b # Show the result img.show()

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3. Fix the indention below to correctly set the red to the green, the green to the blue, and the blue to the red.

   # Step 1: Get the Image object from the PIL library from PIL import Image # Step 2: Connect to the image img = Image.open('beach.jpg') # Step 3: Load the pixels pixels = img.load() # Step 4: Loop through the pixels for x in range(img.size[0]): for y in range(img.size[1]): # Step 5: Get the data r, g, b = pixels[x, y] # Step 6: Modify the color pixels[x, y] = g, b, r # Step 7: Show the result img.show()

4. Fix the 5 errors in the code, so that the Red pixels get the value of the green, the green get the value of blue, and the blue get the value of the red. (The cat should look purple and gray)

   # Step 1: Load the Image class from the PIL library from PIL import Image # Step 2: Connect to the image img = Image.open'kitten.jpg') # Step 3: Load the pixels pixels = imgload() # Step 4: Loop through the pixels for x in range(img.size[]): for y in range(img.size[1]): # Step 5: Get the data r, g, b = pixels[x, y[ # Step 6: Modify the color pixels[x y] = g, b, r # Step 7: Show the result img.show()

5. Fill in the missing code on lines 9, 12, and 18 below to set the red to half the original value in all pixels in the picture.

   # Step 1: Load the Image class from the PIL library from PIL import Image # Step 2: Connect to the image img = Image.load('beach.jpg') # Step 3: Load the pixels pixels = img.load() # Step 4: Loop through the pixels for x in ?? for y in ?? # Step 5: Get the data ?? = ?? # Step 6: Modify the color pixels[x, y] = ??, ??, ?? # Step 7: Show the result img.show()

6. Complete the code in order to set the blue value to an eighth of the green value plus an eighth of the red value.

   from PIL import Image img = Image.open('swan.jpg') pixels = img.load() for x in range(img.size[0]): for y in range(img.size[1]): r, g, b = pixels[x, y] new_b = ?? pixel[x, y] = r, g, new_b img.show()

7. Fix the indention in the code below so that it correctly increases the red in each pixel in the picture by 1.5.

   from PIL import Image img = Image.open('beach.jpg') pixels = img.load() for x in range(img.size[0]): for y in range(img.size[1]): r, g, b = pixels[x, y] pixels[x, y] = int(1.5 * r), g, b img.show()

8. This code is supposed to make the picture completely black; however, it is taking forever when it should only take a few seconds. Fix the code (without adding anything new) so that it runs in a few seconds.

   from PIL import Image img = Image.open('motorcycle.jpg') pixels = img.load() for x in range(img.size[0]): for y in range(img.size[1]): pixels[x, y] = 0, 0, 0 img.show()

9. Fix the code below to correctly set the green and blue values to 0.75 times their current values.

   # Step 1: Import the Image class from the PIL library from PIL import Image # Step 2: Connect to the image img = Image.open('beach.jpg') # Step 3: Load the pixels pixels = img.load() # Step 4: Loop through the pixels for x in range(img.size[0]): for y in range(img.size[1]): # Step 5: Get the data r, g, b = pixels[x, y] # Step 6: Modify the data pixels[x, y] = r, int(??), int(??) # Step 7: Show the result img.show()

10. Write code below to set all the pixels to half their original values. Use the // operator so that the color values are integers.

11. The following code redraws the whole image by drawing the top half and then drawing the bottom half. Change it to set the red to 0 for all pixels in the top and the green to 0 in all the pixels in the bottom of the picture.

    from PIL import Image img = Image.open('gal2.jpg') pixels = img.load() for x in range(img.size[0]): for y in range(img.size[1] // 2): r, g, b = pixels[x, y] pixels[x, y] = r, g, b for y in range(img.size[1] // 2, img.size[1]): r, g, b = pixels[x, y] pixels[x, y] = r, g, b img.show()

12. The code below makes the whole image have a blue-green tint. Change the code so that it makes an only blue tint in the bottom left corner.

    from PIL import Image img = Image.open('vangogh.jpg') pixels = img.load() width = img.size[0] height = img.size[1] for x in range(width): for y in range(height): r, g, b = pixels[x, y] pixels[x, y] = 0, g, b img.show()

13. Change the code below to set the red value in the pixels in the bottom half of the picture to 0.

    from PIL import Image img = Image.open('gal2.jpg') pixels = img.load() width = img.size[0] height = img.size[1] for x in range(width): for y in range(height): r, g, b = pixels[x, y] pixels[x, y] = r, g, b img.show()

14. The code below makes the whole image seem red. Change it, so that only every 5 pixels get changed, so that it will look like a red grid.

    from PIL import Image img = Image.open('guy1.jpg') w = img.size[0] h = img.size[1] pixels = img.load() for x in range(w): for y in range(h): r, g, b = pixels[x, y] pixels[x, y] = r, 0, 0 img.show()

15. Fill in the missing values in the procedure to keep only the green value of each pixels in an image. Call the proceedure with the baby.jpg image to test your result.

    from PIL import Image def show_only_green(image_file_name): img = Image.open(??) w = img.?? h = img.?? pixels = img.load() for x in range(w): for y in range(h): r, g, b = ?? pixels[x, y] = ??, ??, ?? img.show() # call proceedure with the baby.jpg ??

16. A grayscale picture is when the red, green, and blue value of a pixel are all equal to the average of the original pixel value. Write the code to turn the left half of an image into gray scale.

17. Define a procedure to negate an image. See Image_Negate_Quarter from Chapter 11 section 7 for how to create a negative of an image. Pass the image to the procedure. Do the import, create the image, call the prodecure, and show the result.

18. Write code that takes the top half of an image and replicates it in the bottom half.

19. Write a procedure to mirror an image from left to right around a vertical line in the middle of the image. Pass the image to the procedure. Do the import, create the image, call the prodecure, and show the result.

20. Write code that flips the image across a horizontal line.