Refactored code based on this repo (https://github.com/homeless-field/ascii_art)

ascii_art.py

import sys

from PIL import Image

# Setup image
img_orig = Image.open("ctycgchr36231.jpg")
scale = 3

w, h = img_orig.width, img_orig.height
image = img_orig.resize( (w//scale, h//scale) )


# Setup ascii variables
ascii_pixels = ('..', '**', '$$')

max_rgb = max(range(256))
rgb_sub_range = max_rgb / len(ascii_pixels)


def ascii_from_rgb(x, y):
    r, g, b = image.getpixel((x, y))
    avg_brightness = sum([r, g, b]) / len([r, g, b])

    pixel_index = int(avg_brightness / rgb_sub_range)
    ascii_pixel = ascii_pixels[pixel_index]

    return f"{ascii_pixel}" if x < (image.width - 1) \
                else f"{ascii_pixel}\n"


def ascii_art_generator(image):
    return (
        ascii_from_rgb(x, y)
            for y in range(image.height)
            for x in range(image.width)
    )



if __name__ == "__main__":
    ascii_art = ascii_art_generator(image)

    # Pass an optional filename with '-f' flag to save to file:
    # $ python ascii_art.py -f result.txt
    filename, args = "", sys.argv[1:]

    # Trying Python 3.8 walrus operator
    if (len(args) >= 2) and ('-f' in args[0]) and (filename := args[1]):
        with open(filename, 'w') as f:
            for c in ascii_art:
                f.write(c)
    else:
        print(''.join(ascii_art))