Converts an image to Sixel format with optional resizing by width and/or height.

img2sixel.py

import sys
import argparse
import io
from PIL import Image

# https://github.com/sbamboo/python-sixel
import sixel

def main():
    parser = argparse.ArgumentParser(description="Display image in Sixel format with optional resizing.")
    parser.add_argument("image_path", help="Path to the image file")
    parser.add_argument("-W", "--width", type=int, help="Resize width while maintaining aspect ratio")
    parser.add_argument("-H", "--height", type=int, help="Resize height while maintaining aspect ratio")
    args = parser.parse_args()

    # Load the image
    img = Image.open(args.image_path)

    # Resize logic
    if args.width and args.height:
        # Both specified: resize to the given size
        img = img.resize((args.width, args.height), Image.LANCZOS)
    elif args.width:
        # Only width specified: keep aspect ratio
        w_percent = args.width / float(img.size[0])
        h_size = int(float(img.size[1]) * w_percent)
        img = img.resize((args.width, h_size), Image.LANCZOS)
    elif args.height:
        # Only height specified: keep aspect ratio
        h_percent = args.height / float(img.size[1])
        w_size = int(float(img.size[0]) * h_percent)
        img = img.resize((w_size, args.height), Image.LANCZOS)

    # Save to memory buffer and output as Sixel
    with io.BytesIO() as buf:
        img.save(buf, format="PNG")
        buf.seek(0)
        sixel.converter.SixelConverter(buf).write(sys.stdout)

if __name__ == "__main__":
    main()

Details (in Japanese)

https://qiita.com/7shi/items/69d1e7c15c7c6a5bb34f