Python: redimensionar imágenes rellenando con un color de fondo

resize.py

import logging
import os
from PIL import Image

logger = logging.getLogger(__name__)
logging.basicConfig(filename='resize.log', level=logging.DEBUG)

IMG_SIZE = (800, 800)
IMG_MODE = 'RGBA'
IMG_BACKGROUND = (255, 255, 255, 255)


def resize_image(src, output_dir):
    filename = os.path.basename(src).lower()
    dest_file = os.path.join(output_dir, filename)
    logger.debug('Dir. Salida: %s' % output_dir)
    logger.debug("Salida: %s" % dest_file)
    print(os.path.join(output_dir, filename))

    original = Image.open(src)
    original.thumbnail(IMG_SIZE, Image.ANTIALIAS)
    img_width, img_height = original.size
    width, height = IMG_SIZE
    offset = ((width-img_width)//2, (height-img_height)//2)

    image = Image.new(IMG_MODE, IMG_SIZE, IMG_BACKGROUND)
    image.paste(original, offset)
    image.save(dest_file, "JPEG")


if __name__ == "__main__":
    folder = os.path.join(os.getcwd(), 'uploads')
    output_dir = os.path.join(folder, "resized")
    print('Directorio de salida: %s' % output_dir)

    if not os.path.exists(output_dir):
        logger.info('Creado directorio de salida')
        os.mkdir(output_dir)

    for entry in os.scandir(folder):
        if entry.is_file():
            file_path = os.path.join(folder, entry.path)
            logger.info('Imagen: %s' % file_path)
            resize_image(file_path, output_dir)

    print('Proceso terminado')