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

defblackAndWhite(image): """Convertstheargumentimagetoblackandwhite.""" blackPixel=(0,0,0) whitePixel=(255,255,255) foryinrange(image.getHeight()): forxinrange(image.getWidth()): (r,g,b)=image.getPixel(x,y) average=(r+g+b)//3 ifaverage<128: image.setPixel(x,y,blackPixel) else: image.setPixel(x,y,whitePixel) 

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