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"""
Adapted from https://github.com/openai/guided-diffusion/blob/22e0df8183507e13a7813f8d38d51b072ca1e67c/evaluations/evaluator.py
"""
import warnings
import numpy as np
from scipy import linalg
class InvalidFIDException(Exception):
pass
class FIDStatistics:
def __init__(self, mu: np.ndarray, sigma: np.ndarray):
self.mu = mu
self.sigma = sigma
def frechet_distance(self, other, eps=1e-6):
"""
Compute the Frechet distance between two sets of statistics.
"""
# https://github.com/bioinf-jku/TTUR/blob/73ab375cdf952a12686d9aa7978567771084da42/fid.py#L132
mu1, sigma1 = self.mu, self.sigma
mu2, sigma2 = other.mu, other.sigma
mu1 = np.atleast_1d(mu1)
mu2 = np.atleast_1d(mu2)
sigma1 = np.atleast_2d(sigma1)
sigma2 = np.atleast_2d(sigma2)
assert (
mu1.shape == mu2.shape
), f"Training and test mean vectors have different lengths: {mu1.shape}, {mu2.shape}"
assert (
sigma1.shape == sigma2.shape
), f"Training and test covariances have different dimensions: {sigma1.shape}, {sigma2.shape}"
diff = mu1 - mu2
# product might be almost singular
covmean, _ = linalg.sqrtm(sigma1.dot(sigma2), disp=False)
if not np.isfinite(covmean).all():
msg = (
"fid calculation produces singular product; adding %s to diagonal of cov estimates"
% eps
)
warnings.warn(msg)
offset = np.eye(sigma1.shape[0]) * eps
covmean = linalg.sqrtm((sigma1 + offset).dot(sigma2 + offset))
# numerical error might give slight imaginary component
if np.iscomplexobj(covmean):
if not np.allclose(np.diagonal(covmean).imag, 0, atol=1e-3):
m = np.max(np.abs(covmean.imag))
raise ValueError("Imaginary component {}".format(m))
covmean = covmean.real
tr_covmean = np.trace(covmean)
return diff.dot(diff) + np.trace(sigma1) + np.trace(sigma2) - 2 * tr_covmean
def compute_statistics(feats: np.ndarray) -> FIDStatistics:
mu = np.mean(feats, axis=0)
sigma = np.cov(feats, rowvar=False)
return FIDStatistics(mu, sigma)
def compute_inception_score(preds: np.ndarray, split_size: int = 5000) -> float:
# https://github.com/openai/improved-gan/blob/4f5d1ec5c16a7eceb206f42bfc652693601e1d5c/inception_score/model.py#L46
scores = []
for i in range(0, len(preds), split_size):
part = preds[i : i + split_size]
kl = part * (np.log(part) - np.log(np.expand_dims(np.mean(part, 0), 0)))
kl = np.mean(np.sum(kl, 1))
scores.append(np.exp(kl))
return float(np.mean(scores))
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