Define a function named posterize. This function expects an image and a tuple of RGB values as arguments. The function modifies the image like the blackAndWhite function developed in Chapter 7 and shown below, but it uses passed in RGB values instead of black

def posterize(image, bwLevels):
  for pixel in image.getPixels():
    red = pixel.getRed()
    green = pixel.getGreen()
    blue = pixel.getBlue()
    average = (red + green + blue) / 3
        
    if average < bwLevels[0]:
      newRed = bwLevels[0]
      newGreen = bwLevels[0]
      newBlue = bwLevels[0]
    elif average < bwLevels[1]:
      newRed = bwLevels[1]
      newGreen = bwLevels[1]
      newBlue = bwLevels[1]
    elif average < bwLevels[2]:
      newRed = bwLevels[2]
      newGreen = bwLevels[2]
      newBlue = bwLevels[2]
    else:
      newRed = 255
      newGreen = 255
      newBlue = 255
        
    pixel.setRed(newRed)
    pixel.set