如果像素小于特定值，如何迭代pygame 3d surfarray并更改像素的单个颜色？

import pygame
from pygame.locals import *
import numpy as np

pygame.init()
width, height = 800, 600
screen = pygame.display.set_mode((width, height), DOUBLEBUF | OPENGL)

gluPerspective(45, (width / height), 0.1, 50.0)
glTranslatef(0.0, 0.0, -5)

image = pygame.image.load("image.png")
pixels = pygame.surfarray.array3d(image)

for x in range(len(pixels)):
    for y in range(len(pixels[x])):
        for z in range(len(pixels[x][y])):
            if pixels[x][y][z] < 128:
                pixels[x][y][z] = 0  # 更改像素的单个颜色

pygame.surfarray.blit_array(image, pixels)

glDrawPixels(image.get_width(), image.get_height(), GL_RGB, GL_UNSIGNED_BYTE, pixels)
pygame.display.flip()