image_alpha_processor.py

def __mix(back, front, alpha):
    result = 0
    result += round(front * (alpha / 255))
    result += round(back * ((255-alpha) / 255))
    return result

colordic = {}

for f in range(256):
    for a in range(256):
        v1 = __mix(0, f, a)
        v2 = __mix(255, f, a)
        k = (v1, v2)
        if not k in colordic:
            colordic[k] = (f, a)
        elif colordic[k][1] == a:
            pass # we are still okay
        else:
            pass # This is an error case, but I don't know what to do!

from PIL import Image

def generate_transparent_image(black_img, white_img, out_img):
    img1 = Image.open(black_img)
    img2 = Image.open(white_img)
    img3 = Image.new('RGBA', img1.size, (0,0,0,0))


    px1 = img1.load()
    px2 = img2.load()
    px3 = img3.load()

    for x in range(img1.size[0]):
        for y in range(img1.size[1]):
            rgb1 = px1[x,y]
            rgb2 = px2[x,y]
            v1 = rgb1[0]
            v2 = rgb2[0]
            a = colordic[(v1,v2)][1]
            px3[x,y] = rgb1[:3] + (a,)

    img3.save(out_img)

def generate_alpha_image(black_img, white_img, out_img):
    img1 = Image.open(black_img)
    img2 = Image.open(white_img)
    img3 = Image.new('RGBA', img1.size, (0,0,0,0))


    px1 = img1.load()
    px2 = img2.load()
    px3 = img3.load()

    for x in range(img1.size[0]):
        for y in range(img1.size[1]):
            rgb1 = px1[x,y]
            rgb2 = px2[x,y]
            v1 = rgb1[0]
            v2 = rgb2[0]
            a = colordic[(v1,v2)][1]
            px3[x,y] = (a,a,a,255)

    img3.save(out_img)