Compare PDQ Hash performance using pure Python versus bindings to C++ implementation. Results show 262ms for pure Python and 7ms for the bindings.

pdqhash_speed_comparison.py

# Before running this script, you must clone the ThreatExchange
# repo (containing the pure Python implementation) 
# and install the pdqhash package (containing the C bindings).
# You can do this by executing the following at the command line.
# git clone https://github.com/facebook/ThreatExchange.git
# pip install pdqhash

import urllib.request
import timeit
import sys
import os

# Make sure Python can find the Python implementation
sys.path.insert(0, os.path.abspath('ThreatExchange/hashing/pdq/python'))

# Import the bindings package as well as the
# pure Python implementation module
import pdqhashing.hasher.pdq_hasher as pdqpython
import pdqhash as pdqcython
import numpy as np
import cv2

# Download an example image
urllib.request.urlretrieve(
    "https://commons.wikimedia.org/w/thumb.php?f=Actinoscyphia_aurelia_1.jpg&w=256",
    "example.jpg"
)

# We want an apples to apples comparison so
# we include I/O as part of the test for both
# approaches.

pyhasher = pdqpython.PDQHasher()

def pdq_using_cython_bindings(filepath):
    image = cv2.imread(filepath)
    image = cv2.cvtColor(image, cv2.COLOR_BGR2RGB)
    return pdqcython.compute(image)

def pdq_using_pure_python(filepath):
    return pyhasher.fromFile(filepath)

n_runs = 100

print('Running Python benchmark.')
time_python = timeit.timeit(
    stmt="pdq_using_pure_python('example.jpg')",
    globals=globals(),
    number=n_runs
) / n_runs

print('Running Cython bindings benchmark.')
time_cython = timeit.timeit(
    stmt="pdq_using_cython_bindings('example.jpg')", globals=globals(),
    number=n_runs
) / n_runs

# Here we make sure the output is identical for both the bindings and the
# pure Python implementation.
# The reshape operation is used to put the bits in the same order as
# that shown using:
# ./pdq-photo-hasher example.jpg | \
#   cut -d',' -f1 | \
#   ./hashtool256 bits | tr ' ' ','


hqpython = pdq_using_pure_python('example.jpg')
vector_cython, quality_cython = pdq_using_cython_bindings('example.jpg')

np.testing.assert_equal(
    vector_cython.astype('int'),
    np.array(hqpython.getHash().dumpBitsAcross().split(' ')).astype('int').reshape(16, 16)[::-1].flatten()
)
assert quality_cython == hqpython.getQuality()

print(f'Running with pure Python implementation took {round(1000*time_python)}ms, on average.')
print(f'Running with Cython bindings took {round(1000*time_cython)}ms, on average.')