18.8. Multiple Choice Questions

Q-1: What are the three colors parts that make up each pixel?

• red, blue and yellow
• These are the primary colors for paint, but computers use light.
• red, green and blue
• Correct. Computers use red, green, and blue light to make all of the colors.
• red, white and blue
• Try again.
• blue, black and red
• Try again.

Q-2: What does the following code block do?

from image import *
img = Image('beach.jpg')
pixels = img.getPixels()
for p in pixels:
    r = p.getRed()
    p.setGreen(r)
    img.updatePixel(p)

• Sets the green value in every pixel to the red value.
• Correct. It sets the green value to the red value.
• Switches the green and red values in every pixel.
• It only sets the green value, not the red value.
• Creates a green filter on the image.
• What does it set the green value to?
• The code has no effect on pixel color.
• It does change the pixel color.

Q-3: Every pixel has a color with a red value, a green value and a blue value. What is the range (minimum value and maximum value)?

• 0 to 100
• The maximum value is not 100.
• 0 to 255
• Correct. The minimum value is 0 and the maximum is 255.
• 1 to 10
• Neither of these is correct.
• 1 to 255
• The minimum value is not 1.

Q-4: If a pixel has red=0, green=255, and blue=0, what color will it be?

• Red
• Try again. If red equals 0, there will be no red color in the resulting pixel.
• Green
• Correct. Since green equals 255 and the other two values equal 0, the resulting pixel color will be green.
• Black
• Try again. All values must be 0 for the pixel to be black.
• Blue
• Try again. If blue equals 0, there will be no blue color in the resulting pixel.
• White
• Try again. All values must be 255 for the pixel to be white.

Q-5: Which code block should you insert in the for loop below to correctly increase the blue by 180%?

from image import *

img = Image("motorcycle.jpg")
pixels = img.getPixels()

for p in pixels:
    #INSERT LINES HERE
    img.updatePixel(p)
win = ImageWin(img.getWidth(), img.getHeight())
img.draw(win)

I.

r = p.getRed()
p.setRed(r * 180)

II.

b = p.getBlue()
p.setBlue(b * 1.8)

III.

b = p.getBlue()
p.setBlue(b * 180)

IV.

p.setBlue(b * 1.8)

• I
• No, this code would increase red, not blue, by 180%.
• II
• Correct.
• III
• No, you have to convert the percentage you want to increase by into a decimal. If you want to increase a color by 180%, you would multiply by 1.8.
• IV
• No, you have to get the blue value first in order to increase it by a certain amount.

Q-6: Which of the following would reduce the green value by 25%?

• multiply the green value by 25
• To reduce the green value you must multiply by a value that is less than 1.
• multiply the green value by 0.25
• This would reduce it by 75%.
• multiply the green value by 0.5
• This would reduce it by 50%.
• multiply the green value by 0.75
• This would reduce it by 25%.

Q-7: Which code block would allow you to copy the bottom half of the image onto the top half?

I.

from image import *
img = Image("vangogh.jpg")

halfway = (int) (img.getHeight() / 2)
for x in range(img.getWidth()):
    for y in range(halfway, img.getHeight()):
        p = img.getPixel(x, y)
        r = p.getRed()
        g = p.getGreen()
        b = p.getBlue()
        newPixel = Pixel(r, g, b)
        img.setPixel(x, y - halfway, newPixel)

win = ImageWin(img.getWidth(),img.getHeight())
img.draw(win)

II.

from image import *
img = Image("vangogh.jpg")

halfway = (int) (img.getWidth() / 2)
for x in range(halfway):
    for y in range(img.getHeight()):
        p = img.getPixel(x, y)
        r = p.getRed()
        g = p.getGreen()
        b = p.getBlue()
        newPixel = Pixel(r, g, b)
        img.setPixel(halfway + x, y, newPixel)

win = ImageWin(img.getWidth(),img.getHeight())
img.draw(win)

III.

from image import *
img = Image("vangogh.jpg")

halfway_x = (int) (img.getWidth() / 2)
halfway_y = (int) (img.getHeight() / 2)
for x in range(halfway_x):
    for y in range(halfway_y):
        p = img.getPixel(x, y)
        r = p.getRed()
        g = p.getGreen()
        b = p.getBlue()
        newPixel = Pixel(r, g, b)
        img.setPixel(x, halfway_y + y, newPixel)

win = ImageWin(img.getWidth(),img.getHeight())
img.draw(win)

IV.

from image import *
img = Image("vangogh.jpg")

halfway = (int) (img.getHeight() / 2)
for x in range(img.getWidth()):
    for y in range(halfway):
        p = img.getPixel(x, y)
        r = p.getRed()
        g = p.getGreen()
        b = p.getBlue()
        newPixel = Pixel(r, g, b)
        img.setPixel(x, halfway + y, newPixel)

win = ImageWin(img.getWidth(),img.getHeight())
img.draw(win)

• I
• Correct. This code block copies from the bottom half of the image to the top half.
• II
• Try again. This code block copies from the left half to the right half.
• III
• Try again. This code block copies the top left quadrant to the bottom left quadrant.
• IV
• Try again. This code block copies the top half of the image onto the bottom of the image.

Q-8: Which of the following combinations of red (r), green (g), and blue (b) values makes white?

• r = 255, g = 0, b = 0
• This would be red.
• r = 0, g = 0, b = 0
• This would be black (no light).
• r = 0, g = 255, b = 0
• This would be green
• r = 255, g = 255, b = 255
• Correct. To make white set all values to 255.

Q-9: What happens when we run the following code?

from image import *
img = Image("vangogh.jpg")

for x in range(img.getWidth()):
    for y in range(img.getHeight()):
        p = img.getPixel(x, y)
        img.setPixel(img.getWidth() - 1 - y,
                     img.getHeight() - 1 - x,
                     p)

win = ImageWin(img.getWidth(),img.getHeight())
img.draw(win)

• The image is rotated 90 degree to the right.
• We would have to create a new image and set the values in the new image from the old pixel values for this to be true.
• The image is mirrored around a diagonal line from the top left to the bottom right.
• Close, try again!
• The image is mirrored vertically.
• This would be true if the pixels were copied to the same row.
• The image is mirrored around a diagonal line from the top right to the bottom left.
• Correct.

Q-10: What line of code sets the red, green and blue values simultaneously?

• setPixel(r, g, b)
• There is no setPixel method.
• Pixel(r, g, b)
• Correct. You can set the red, blue, and green when you create a Pixel.
• setAll(r, g, b)
• There is no setAll method.
• This cannot be accomplished using a single line of code.
• You can actually set the red, blue, and green at the same time.

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