pytorch-sfid

Computing the Sliding Fréchet Inception Distance (SFID) between fake and real images with continous conditions, as suggested by Ding et al., 2021. The package is heavily inspired by pytorch-fid-wrapper, which again is based on pytorch-fid.

NB: For ncenters given intervals and ncond conditions, the images are sorted in ncenters^ncond number of (overlapping) bins. Since this number of bins increases rapidly with ncond, a large number of conditions will cause out-of-memory error. In practice, up to 5 conditions is possible for a standard computer.

Install

pip install git+https://github.com/evenmn/pytorch-sfid

Prerequisites

1. torch
2. pytorch-fid-wrapper

Usage

The package is centered around a function get_sfid, which takes a set of real and fake images and the corresponding conditions as torch tensors. The function set_config might be used to change the default ncenters and radius, but they can also be specified on-the-fly:

import pytorch_sfid as ps

# optional
ps.set_config(ncenters=NCENTERS, radius=RADIUS, batch_size=BATCH_SIZE, dims=DIMS, device=DEVICE)

# optional
real_stats = ps.get_stats(real_images=REAL_IMAGES, real_attr=REAL_ATTR)

# get SFID
sfid = ps.get_sfid(FAKE_IMAGES, FAKE_ATTR, real_images=REAL_IMAGES, real_attr=REAL_ATTR)

or

sfid = ps.get_sfid(FAKE_IMAGES, FAKE_ATTR, real_stats=real_stats)

The number of centers and the radius should be chosen such that most bins will contain sufficiently many images.

What does the code do?

The attributes are sorted into bins based on overlapping intervals. Then the indices of the images residing each bin is stored in an ncond x ncentersx nimg tensor, which is iterated. For each bin, we obtain the FID-score of the images, and the SFID score is found from summing over the FID score of all the bins:

.

The code itself utilizes torch only, and should be sufficiently fast. However, to find the FID values, we use pytorch-fid, which can be perceived as slow (even though it is as fast as it can be).

To do

1. Make more conditions possible by ignoring certain conditions or merge bins of similar conditions.
2. Allow different ncenters and radii for different conditions

Acknowledgements

I will kindly thank Halvard Sutterud (@halvarsu) for implementation help and mental support during the development of this package.

License

APACHE LICENSE, VERSION 2.0