See https://github.com/webcompat/webcompat.com/issues/1942

resize-filter.py

from PIL import Image
import time

FILTER_LIST = [('nearest', Image.NEAREST),
               ('bilinear', Image.BILINEAR),
               ('bicubic', Image.BICUBIC),
               ('lanczos', Image.LANCZOS),
               ('antialias', Image.ANTIALIAS)]
FILE = '/Users/karl/Documents/2016/10/12/thumbnail-test/original.png'
SIZE = (500, 500)

original = Image.open(FILE)

for thumb_name, img_filter in FILTER_LIST:
    # We put the cursor at the start
    original2 = original.copy()
    thumb_name = 'thumb_{}.jpg'.format(thumb_name)
    # Creating the thumbnail
    start = time.time()
    original2.thumbnail(SIZE, img_filter)
    middle = time.time()
    original2 = original2.convert('RGB')
    middle2 = time.time()
    original2.save(thumb_name, 'JPEG')
    end = time.time()
    thumb_duration = round(middle - start, 4)
    convert_duration = round(middle2 - middle, 4)
    save_duration = round(end - middle2, 4)
    total = round(end - start, 4)
    print('''
    {thumb_name}:
        creating thumbnail {thumb_duration} seconds
        convert to RGB     {convert_duration} seconds
        save thumbnail     {save_duration} seconds
        ---------------------------------------------
        total = {total} seconds
    '''.format(thumb_name=thumb_name,
               thumb_duration=thumb_duration,
               convert_duration=convert_duration,
               save_duration=save_duration,
               total=total))