Edit photo - Pencil sketch effect - Image processing in Python

Code:
from skimage import data, io, util
import random
import sys
from skimage.color import rgb2gray

try:
    rgb_image = data.imread(sys.argv[1])
   
    height = rgb_image.shape[0]
    width = rgb_image.shape[1]
   
    if(len(rgb_image.shape) == 3):
        rgb_image = util.img_as_ubyte(rgb2gray(rgb_image))
    for i in range(height):
        for j in range(width):
            if rgb_image[i,j] < 128:
                rgb_image[i,j] = 15
            else:
                rgb_image[i,j] = 240
   
    io.imsave("pencil_sketch.jpg", rgb_image)
   
except Exception as e:
    print(e)


Original Image (RGB):

Pencil Sketch:

Original Image (Grayscale):

Pencil Sketch: