Change an image to have a transparency

maketransparent.py

from PIL import Image
import numpy as np

if __name__ == "__main__":
	im = Image.open("in.png")
	pix = im.load()

	imgOut = Image.new("RGBA", im.size)
	pixOut = imgOut.load()

	bgCol = np.array([54,40,29])
	fgCol = np.array([255,255,255])
	dCol = fgCol - bgCol
	dColMag = np.power(np.sum(np.power(dCol, 2.0)),0.5)
	dCol = dCol / dColMag

	for x in range(im.size[0]):	
		for y in range(im.size[1]):
			a = ((pix[x,y] - bgCol) / dColMag).dot(dCol)
			pixOut[x,y] = (255,255,255,int(round(a*255.0)))
	
	imgOut.save("out.png")