Im trying to figure out how to make this code print out a gray scale image. My teacher wants us to use this code to make it yet I've been stuck

Question

from cImage import *
fileImageName = "butterfly.png"

def getNegativePixel(oldPixel):
    newRed = 255 - oldPixel.getRed()
    newGreen = 255 - oldPixel.getGreen()
    newBlue = 255 - oldPixel.getBlue()
    newPixel = Pixel(newRed, newGreen, newBlue)
    return newPixel

def makeNegativeImage(imageFile):
    oldImage = FileImage(imageFile)
    oHeight = oldImage.getHeight()
    oWidth = oldImage.getWidth()

    myWindow = ImageWin("Negative Butterfly Image",oWidth * 2, oHeight)
    oldImage.draw(myWindow)

    newImage = EmptyImage(oWidth,oHeight)

    for row in range(oHeight):
        for column in range(oWidth):
            oldPixel = oldImage.getPixel(column, row)
            newPixel = getNegativePixel(oldPixel)
            newImage.setPixel( column, row,newPixel )


    
    newImage.setPosition(oWidth + 1, 0)
    newImage.draw(myWindow)
    
    myWindow.exitOnClick()


makeNegativeImage(fileImageName)

I have just been stuck with it tried changing certain variables but couldn't really work it out. Ive tried asking them for help but didnt really provide so im hoping someone would know how to do it, so i could better understand how to make it work