用Python平滑调整大小的图像（如何像计算机科学家一样思考）

Question

我被[“如何像一个计算机科学家一样思考”]（http://interactivepython.org/runestone/static/thinkcspy/MoreAboutIteration/Exercises.html）提供的这个练习：

After you have scaled an image too much it looks blocky. One way of reducing the blockiness of the image is to replace each pixel with the average values of the pixels around it. This has the effect of smoothing out the changes in color. Write a function that takes an image as a parameter and smooths the image. Your function should return a new image that is the same as the old but smoothed.

以下是我的源代码：

def smooth(img):
for i in range(img.getWidth()):
    for j in range(img.getHeight()):
        #first step: get surrounding pixels
        #top pixel
        ptopcenter = img.getPixel(i,j-1)
        ptopleft = img.getPixel(i-1,j-1)
        ptopright = img.getPixel(i+1,j-1)

        #center pixel
        pcent = img.getPixel(i,j)
        pcentleft = img.getPixel(i-1,j)
        pcentright = img.getPixel(i+1,j)

        #bottom pixel
        pbotcenter = img.getPixel(i,j+1)
        pbotleft = img.getPixel(i-1,j+1)
        pbotright = img.getPixel(i+1,j+1)

        #second step: average pixels
        p1Red = ptopcenter.getRed()
        p1Blue = ptopcenter.getBlue()
        p1Green = ptopcenter.getGreen()

        p2Red = ptopcenter.getRed()
        p2Blue = ptopcenter.getBlue()
        p2Green = ptopcenter.getGreen()

        p3Red = ptopright.getRed()
        p3Blue = ptopright.getRed()
        p3Green = ptopright.getRed()

        p4Red = pcentleft.getRed()
        p4Blue = pcentleft.getBlue()
        p4Green = pcentleft.getGreen()

        p5Red = pcentright.getRed()
        p5Blue = pcentright.getBlue()
        p5Green = pcentright.getGreen()

        p6Red = pbotleft.getRed()
        p6Blue = pbotleft.getBlue()
        p6Green = pbotleft.getGreen()

        p7Red = pbotcenter.getRed()
        p7Blue = pbotcenter.getBlue()
        p7Green = pbotcenter.getGreen()

        p8Red = pbotright.getRed()
        p8Blue = pbotright.getBlue()
        p8Green = pbotright.getGreen()

        #average all the colors
        pavgRed = (p1Red + p2Red + p3Red + p4Red + p5Red + p6Red + p7Red + p8Red)/8
        pavgBlue = (p1Blue + p2Blue + p3Blue + p4Blue + p5Blue + p6Blue + p7Blue + p8Blue)/8
        pavgGreen = (p1Green + p2Green + p3Green + p4Green + p5Green + p6Green + p7Green + p8Green)/8

        pcent.setRed(pavgRed)
        pcent.setGreen(pavgGreen)
        pcent.setBlue(pavgBlue)