def draw_background(setup) :
	canvas = setup['canvas']

	image = Image.new('RGBA', canvas, tuple(setup['color']['back']))
	background = Image.new('RGBA', canvas, (0,0,0,0))
	draw = ImageDraw.Draw(background)

	stars = [[ int(p * random()) for p in canvas ] for x in range(400) ]
	scale = lambda x, r : x + r * (min(canvas) / 320)
	color = (255, 255, 255, 100)

	for x, y in stars :
		r = random()
		draw.ellipse([x, y, scale(x, r), scale(y, r)], fill=color)

	return Image.alpha_composite(image, background)