Python script to add drop shadows to *.png files in a directory

add_drop_shadow.py

#
# Copyright (c) 2023 Alex Spataru <https://github.com/alex-spataru>
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
#

import os
import re
import argparse

from PIL import Image, ImageFilter, ImageChops

def add_drop_shadow(image_path, output_path, multiplier=1):
    """Add a drop shadow to an image.

    Args:
        image_path (str): Path to the source image.
        output_path (str): Path to save the image with shadow.
        multiplier (int): Image resolution multiplier (1 for standard, >1 for HiDPI).
    """
    # Load the image
    img = Image.open(image_path).convert("RGBA")

    # Blur radius calculation based on multiplier
    blur_radius = 7.5 * multiplier

    # Generate shadow
    shadow = img.filter(ImageFilter.GaussianBlur(blur_radius))
    shadow = ImageChops.multiply(shadow, Image.new("RGBA", img.size, (0, 0, 0, 150)))

    # Crop the shadow so it fits within the image boundaries
    x0 = (shadow.width - img.width) // 2
    y0 = (shadow.height - img.height) // 2
    shadow = shadow.crop((x0, y0, x0 + img.width, y0 + img.height))

    # Combine original image and shadow
    result = Image.alpha_composite(shadow, img)

    # Save result
    result.save(output_path)

if __name__ == '__main__':
    # CLI Argument Parsing
    parser = argparse.ArgumentParser(description='Add drop shadow to all PNG images in a directory.')
    parser.add_argument('dir', type=str, help='The directory containing the images')
    args = parser.parse_args()

    # Create output directory
    output_dir = f"{args.dir}_shadow"
    os.makedirs(output_dir, exist_ok=True)

    # Process all PNG images in the directory
    for filename in os.listdir(args.dir):
        if filename.endswith(".png"):
            full_path = os.path.join(args.dir, filename)
            output_path = os.path.join(output_dir, filename)
            
            # Extract multiplier from filename using regex
            match = re.search(r"@(\d+)x", filename)
            multiplier = int(match.group(1)) if match else 1

            add_drop_shadow(full_path, output_path, multiplier=multiplier)

            print(f"Added drop shadow to {filename}")