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# sources:
# https://www.kaggle.com/code/ibtesama/gan-in-pytorch-with-fid/notebook
# https://github.com/mseitzer/pytorch-fid/blob/master/src/pytorch_fid/fid_score.py
import numpy as np
from scipy import linalg
from torch.nn.functional import adaptive_avg_pool2d
def calculate_activation_statistics(images, model, batch_size=128, dims=2048):
model.eval()
act = np.empty((len(images), dims))
batch = images
pred = model(batch)[0]
# If model output is not scalar, apply global spatial average pooling.
# This happens if you choose a dimensionality not equal 2048.
if pred.size(2) != 1 or pred.size(3) != 1:
pred = adaptive_avg_pool2d(pred, output_size=(1, 1))
act = pred.cpu().data.numpy().reshape(pred.size(0), -1)
mu = np.mean(act, axis=0)
sigma = np.cov(act, rowvar=False)
return mu, sigma
def calculate_frechet_distance(mu1, sigma1, mu2, sigma2, eps=1e-6):
"""Numpy implementation of the Frechet Distance.
The Frechet distance between two multivariate Gaussians X_1 ~ N(mu_1, C_1)
and X_2 ~ N(mu_2, C_2) is
d^2 = ||mu_1 - mu_2||^2 + Tr(C_1 + C_2 - 2*sqrt(C_1*C_2)).
"""
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, \
'Training and test mean vectors have different lengths'
assert sigma1.shape == sigma2.shape, \
'Training and test covariances have different dimensions'
diff = mu1 - mu2
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
print(msg)
offset = np.eye(sigma1.shape[0]) * eps
covmean = linalg.sqrtm((sigma1 + offset).dot(sigma2 + offset))
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 calculate_fretchet(images_real, images_fake, model):
"""Calculate the fretched distance."""
# calculate statistics (mean + std)
mu_1, std_1 = calculate_activation_statistics(images_real, model)
mu_2, std_2 = calculate_activation_statistics(images_fake, model)
# compute distance
fid_value = calculate_frechet_distance(mu_1, std_1, mu_2, std_2)
return fid_value |