vignette_effect.py

import math
import numpy as np
from PIL import Image

img = Image.open("input_image.png")
image_np = np.array(img, dtype = np.float32)
dark_r = np.quantile(image_np[:,:,0:1], 0.1)
dark_g = np.quantile(image_np[:,:,1:2], 0.1)
dark_b = np.quantile(image_np[:,:,2:3], 0.1)

for j in range(512):
  for i in range(512):
    d = math.sqrt((j-256.0) * (j-256) + (i-256.0) * (i-256))
    alpha = 1.0
    if d > 180:
      alpha = math.sin(d*math.pi/360)
    new_pix = image_np[j,i,:] * alpha + np.array([dark_r, dark_g, dark_b]) * (1.0 - alpha)
    image_np[j,i,:] = image_np[j,i,:]*0.25 + new_pix*0.75

image_int = image_np.round().clip(0, 255).astype(np.uint8)
image_pil = Image.fromarray(image_int)
image_pil.save("output_image.png")