binary_pic.py

from PIL import Image


def binary(filename):
    image = Image.open(filename)

    # Convert to Gray mode
    image = image.convert('L')


    maxBetween = 0.0

    size = image.size
    width = size[0]
    height = size[1]
    n = width * height

    out = Image.new('L', size)
    put_data = out.load()

    data = image.load()

    for t in xrange(256):
        n1, n2, s1, s2 = 0, 0, 0, 0

        for i in xrange(width):
            for j in xrange(height):
                if data[i, j] < t:
                    n1 = n1 + 1
                    s1 = s1 + data[i, j]
                else:
                    n2 = n2 + 1
                    s2 = s2 + data[i, j]

        if n1 == 0 or n2 == 0:
            continue

        w1 = 1.0 * n1 / n
        w2 = 1.0 * n2 / n
        u1 = 1.0 * s1 / n1
        u2 = 1.0 * s2 / n2

        between = w1 * w2 * (u1 - u2) ** 2

        if n1 > 0 and n2 > 0 and maxBetween < between:
            maxBetween = between
            threshold = t

    for i in xrange(width):
        for j in xrange(height):
            put_data[i, j] = 255 if data[i, j] > threshold else 0

    out.save('out.jpg')