遗传算法图像演化结果不正确

Question

我正在尝试实现一个最初由Roger Alsing创建的程序。我做了很多研究，看看其他人是怎么实现的。我决定用Python来写这个程序，并使用基本的三角形作为形状。当我运行程序时，经过多代后并没有显示出改进（这些三角形似乎只是消失了）。我猜我的变异函数可能有问题。有没有人能告诉我为什么结果不太理想呢？

我的代码：

import random
import copy
from PIL import Image, ImageDraw

optimal = Image.open("mona_lisa.png")
optimal = optimal.convert("RGBA")

size = width, height = optimal.size

num_shapes = 128

generations = 50000

def random_genome():
    elements = []

    for i in range(num_shapes):
        x = (random.randint(0, width), random.randint(0, height))
        y = (random.randint(0, width), random.randint(0, height))
        z = (random.randint(0, width), random.randint(0, height))
        r = random.randint(0, 255)
        g = random.randint(0, 255)
        b = random.randint(0, 255)
        alpha = random.randint(10, 255)

        elements.append([x, y, z, r, g, b, alpha])

    return elements

def render_daughter(dna):
    image = Image.new("RGBA", (width, height), "white")
    draw = ImageDraw.Draw(image)

    for item in dna:
        x = item[0]
        y = item[1]
        z = item[2]
        r = item[3]
        g = item[4]
        b = item[5]
        alpha = item[6]

        color = (r, g, b, alpha)

        draw.polygon([x, y, z], fill = color)

    return image

def mutate(dna):
    dna_copy = copy.deepcopy(dna)

    shape_index = random.randint(0, len(dna) - 1)
    roulette = random.random() * 2

    if roulette < 1:

        if roulette < 0.25:
            dna_copy[shape_index][3] = int(random.triangular(255, dna_copy[shape_index][3]))

        elif roulette < 0.5:
            dna_copy[shape_index][4] = int(random.triangular(255, dna_copy[shape_index][4]))

        elif roulette < 0.75:
            dna_copy[shape_index][5] = int(random.triangular(255, dna_copy[shape_index][5]))

        elif roulette < 1.0:
            dna_copy[shape_index][6] = int(0.00390625 * random.triangular(255, dna_copy[shape_index][6] * 255))

    else:

        if roulette < 1.25:
            dna_copy[shape_index][0] = (int(random.triangular(width, dna_copy[shape_index][0][0])), int(random.triangular(height, dna_copy[shape_index][0][1])))

        elif roulette < 1.5:
            dna_copy[shape_index][2] = (int(random.triangular(width, dna_copy[shape_index][3][0])), int(random.triangular(height, dna_copy[shape_index][4][1])))

        elif roulette < 1.75:
            dna_copy[shape_index][3] = (int(random.triangular(width, dna_copy[shape_index][4][0])), int(random.triangular(height, dna_copy[shape_index][5][1])))

    return dna_copy

def fitness(original, new):
    fitness = 0

    for x in range(0, width):
        for y in range(0, height):
            r1, g1, b1, a1 = original.getpixel((x, y))
            r2, g2, b2, a2 = new.getpixel((x, y))

            deltaRed = r1 - r2
            deltaGreen = g1 - g2
            deltaBlue = b1 - b2
            deltaAlpha = a1 - a2

            pixelFitness = deltaRed + deltaGreen + deltaBlue + deltaAlpha

            fitness += pixelFitness

    return fitness

def generate():
    mother = random_genome()
    best_genome = mother
    best_fitness = fitness(optimal, render_daughter(best_genome))


    for i in range(generations):
        daughter = copy.deepcopy(best_genome)
        daughter = mutate(daughter)

        daughter_fitness = fitness(optimal, render_daughter(daughter))

        if daughter_fitness < best_fitness:
            best_genome = daughter
            best_fitness = daughter_fitness

        if i % 50 == 0:
            print i

        if i % 1000 == 0:
            render_daughter(best_genome).save("iterations/output_" + str(i) + ".png")

if __name__ == "__main__":
    generate()

我使用的初始图像：

Mona Lisa