climategan/fid.py

# from https://github.com/mseitzer/pytorch-fid

import numpy as np
import torch
import torch.nn as nn
import torch.nn.functional as F
import torchvision
from scipy import linalg
from torch.nn.functional import adaptive_avg_pool2d

try:
    from torchvision.models.utils import load_state_dict_from_url
except ImportError:
    from torch.utils.model_zoo import load_url as load_state_dict_from_url

FID_WEIGHTS_URL = (
    "https://github.com/mseitzer/pytorch-fid/releases/download/"
    + "fid_weights/pt_inception-2015-12-05-6726825d.pth"
)


class InceptionV3(nn.Module):
    """Pretrained InceptionV3 network returning feature maps"""

    # Index of default block of inception to return,
    # corresponds to output of final average pooling
    DEFAULT_BLOCK_INDEX = 3

    # Maps feature dimensionality to their output blocks indices
    BLOCK_INDEX_BY_DIM = {
        64: 0,  # First max pooling features
        192: 1,  # Second max pooling features
        768: 2,  # Pre-aux classifier features
        2048: 3,  # Final average pooling features
    }

    def __init__(
        self,
        output_blocks=[DEFAULT_BLOCK_INDEX],
        resize_input=True,
        normalize_input=True,
        requires_grad=False,
        use_fid_inception=True,
    ):
        """Build pretrained InceptionV3
        Parameters
        ----------
        output_blocks : list of int
            Indices of blocks to return features of. Possible values are:
                - 0: corresponds to output of first max pooling
                - 1: corresponds to output of second max pooling
                - 2: corresponds to output which is fed to aux classifier
                - 3: corresponds to output of final average pooling
        resize_input : bool
            If true, bilinearly resizes input to width and height 299 before
            feeding input to model. As the network without fully connected
            layers is fully convolutional, it should be able to handle inputs
            of arbitrary size, so resizing might not be strictly needed
        normalize_input : bool
            If true, scales the input from range (0, 1) to the range the
            pretrained Inception network expects, namely (-1, 1)
        requires_grad : bool
            If true, parameters of the model require gradients. Possibly useful
            for finetuning the network
        use_fid_inception : bool
            If true, uses the pretrained Inception model used in Tensorflow's
            FID implementation. If false, uses the pretrained Inception model
            available in torchvision. The FID Inception model has different
            weights and a slightly different structure from torchvision's
            Inception model. If you want to compute FID scores, you are
            strongly advised to set this parameter to true to get comparable
            results.
        """
        super(InceptionV3, self).__init__()

        self.resize_input = resize_input
        self.normalize_input = normalize_input
        self.output_blocks = sorted(output_blocks)
        self.last_needed_block = max(output_blocks)

        assert self.last_needed_block <= 3, "Last possible output block index is 3"

        self.blocks = nn.ModuleList()

        if use_fid_inception:
            inception = fid_inception_v3()
        else:
            inception = _inception_v3(pretrained=True)

        # Block 0: input to maxpool1
        block0 = [
            inception.Conv2d_1a_3x3,
            inception.Conv2d_2a_3x3,
            inception.Conv2d_2b_3x3,
            nn.MaxPool2d(kernel_size=3, stride=2),
        ]
        self.blocks.append(nn.Sequential(*block0))

        # Block 1: maxpool1 to maxpool2
        if self.last_needed_block >= 1:
            block1 = [
                inception.Conv2d_3b_1x1,
                inception.Conv2d_4a_3x3,
                nn.MaxPool2d(kernel_size=3, stride=2),
            ]
            self.blocks.append(nn.Sequential(*block1))

        # Block 2: maxpool2 to aux classifier
        if self.last_needed_block >= 2:
            block2 = [
                inception.Mixed_5b,
                inception.Mixed_5c,
                inception.Mixed_5d,
                inception.Mixed_6a,
                inception.Mixed_6b,
                inception.Mixed_6c,
                inception.Mixed_6d,
                inception.Mixed_6e,
            ]
            self.blocks.append(nn.Sequential(*block2))

        # Block 3: aux classifier to final avgpool
        if self.last_needed_block >= 3:
            block3 = [
                inception.Mixed_7a,
                inception.Mixed_7b,
                inception.Mixed_7c,
                nn.AdaptiveAvgPool2d(output_size=(1, 1)),
            ]
            self.blocks.append(nn.Sequential(*block3))

        for param in self.parameters():
            param.requires_grad = requires_grad

    def forward(self, inp):
        """Get Inception feature maps
        Parameters
        ----------
        inp : torch.autograd.Variable
            Input tensor of shape Bx3xHxW. Values are expected to be in
            range (0, 1)
        Returns
        -------
        List of torch.autograd.Variable, corresponding to the selected output
        block, sorted ascending by index
        """
        outp = []
        x = inp

        if self.resize_input:
            x = F.interpolate(x, size=(299, 299), mode="bilinear", align_corners=False)

        if self.normalize_input:
            x = 2 * x - 1  # Scale from range (0, 1) to range (-1, 1)

        for idx, block in enumerate(self.blocks):
            x = block(x)
            if idx in self.output_blocks:
                outp.append(x)

            if idx == self.last_needed_block:
                break

        return outp


def _inception_v3(*args, **kwargs):
    """Wraps `torchvision.models.inception_v3`
    Skips default weight initialization if supported by torchvision version.
    See https://github.com/mseitzer/pytorch-fid/issues/28.
    """
    try:
        version = tuple(map(int, torchvision.__version__.split(".")[:2]))
    except ValueError:
        # Just a caution against weird version strings
        version = (0,)

    if version >= (0, 6):
        kwargs["init_weights"] = False

    return torchvision.models.inception_v3(*args, **kwargs)


def fid_inception_v3():
    """Build pretrained Inception model for FID computation
    The Inception model for FID computation uses a different set of weights
    and has a slightly different structure than torchvision's Inception.
    This method first constructs torchvision's Inception and then patches the
    necessary parts that are different in the FID Inception model.
    """
    inception = _inception_v3(num_classes=1008, aux_logits=False, pretrained=False)
    inception.Mixed_5b = FIDInceptionA(192, pool_features=32)
    inception.Mixed_5c = FIDInceptionA(256, pool_features=64)
    inception.Mixed_5d = FIDInceptionA(288, pool_features=64)
    inception.Mixed_6b = FIDInceptionC(768, channels_7x7=128)
    inception.Mixed_6c = FIDInceptionC(768, channels_7x7=160)
    inception.Mixed_6d = FIDInceptionC(768, channels_7x7=160)
    inception.Mixed_6e = FIDInceptionC(768, channels_7x7=192)
    inception.Mixed_7b = FIDInceptionE_1(1280)
    inception.Mixed_7c = FIDInceptionE_2(2048)

    state_dict = load_state_dict_from_url(FID_WEIGHTS_URL, progress=True)
    inception.load_state_dict(state_dict)
    return inception


class FIDInceptionA(torchvision.models.inception.InceptionA):
    """InceptionA block patched for FID computation"""

    def __init__(self, in_channels, pool_features):
        super(FIDInceptionA, self).__init__(in_channels, pool_features)

    def forward(self, x):
        branch1x1 = self.branch1x1(x)

        branch5x5 = self.branch5x5_1(x)
        branch5x5 = self.branch5x5_2(branch5x5)

        branch3x3dbl = self.branch3x3dbl_1(x)
        branch3x3dbl = self.branch3x3dbl_2(branch3x3dbl)
        branch3x3dbl = self.branch3x3dbl_3(branch3x3dbl)

        # Patch: Tensorflow's average pool does not use the padded zero's in
        # its average calculation
        branch_pool = F.avg_pool2d(
            x, kernel_size=3, stride=1, padding=1, count_include_pad=False
        )
        branch_pool = self.branch_pool(branch_pool)

        outputs = [branch1x1, branch5x5, branch3x3dbl, branch_pool]
        return torch.cat(outputs, 1)


class FIDInceptionC(torchvision.models.inception.InceptionC):
    """InceptionC block patched for FID computation"""

    def __init__(self, in_channels, channels_7x7):
        super(FIDInceptionC, self).__init__(in_channels, channels_7x7)

    def forward(self, x):
        branch1x1 = self.branch1x1(x)

        branch7x7 = self.branch7x7_1(x)
        branch7x7 = self.branch7x7_2(branch7x7)
        branch7x7 = self.branch7x7_3(branch7x7)

        branch7x7dbl = self.branch7x7dbl_1(x)
        branch7x7dbl = self.branch7x7dbl_2(branch7x7dbl)
        branch7x7dbl = self.branch7x7dbl_3(branch7x7dbl)
        branch7x7dbl = self.branch7x7dbl_4(branch7x7dbl)
        branch7x7dbl = self.branch7x7dbl_5(branch7x7dbl)

        # Patch: Tensorflow's average pool does not use the padded zero's in
        # its average calculation
        branch_pool = F.avg_pool2d(
            x, kernel_size=3, stride=1, padding=1, count_include_pad=False
        )
        branch_pool = self.branch_pool(branch_pool)

        outputs = [branch1x1, branch7x7, branch7x7dbl, branch_pool]
        return torch.cat(outputs, 1)


class FIDInceptionE_1(torchvision.models.inception.InceptionE):
    """First InceptionE block patched for FID computation"""

    def __init__(self, in_channels):
        super(FIDInceptionE_1, self).__init__(in_channels)

    def forward(self, x):
        branch1x1 = self.branch1x1(x)

        branch3x3 = self.branch3x3_1(x)
        branch3x3 = [
            self.branch3x3_2a(branch3x3),
            self.branch3x3_2b(branch3x3),
        ]
        branch3x3 = torch.cat(branch3x3, 1)

        branch3x3dbl = self.branch3x3dbl_1(x)
        branch3x3dbl = self.branch3x3dbl_2(branch3x3dbl)
        branch3x3dbl = [
            self.branch3x3dbl_3a(branch3x3dbl),
            self.branch3x3dbl_3b(branch3x3dbl),
        ]
        branch3x3dbl = torch.cat(branch3x3dbl, 1)

        # Patch: Tensorflow's average pool does not use the padded zero's in
        # its average calculation
        branch_pool = F.avg_pool2d(
            x, kernel_size=3, stride=1, padding=1, count_include_pad=False
        )
        branch_pool = self.branch_pool(branch_pool)

        outputs = [branch1x1, branch3x3, branch3x3dbl, branch_pool]
        return torch.cat(outputs, 1)


class FIDInceptionE_2(torchvision.models.inception.InceptionE):
    """Second InceptionE block patched for FID computation"""

    def __init__(self, in_channels):
        super(FIDInceptionE_2, self).__init__(in_channels)

    def forward(self, x):
        branch1x1 = self.branch1x1(x)

        branch3x3 = self.branch3x3_1(x)
        branch3x3 = [
            self.branch3x3_2a(branch3x3),
            self.branch3x3_2b(branch3x3),
        ]
        branch3x3 = torch.cat(branch3x3, 1)

        branch3x3dbl = self.branch3x3dbl_1(x)
        branch3x3dbl = self.branch3x3dbl_2(branch3x3dbl)
        branch3x3dbl = [
            self.branch3x3dbl_3a(branch3x3dbl),
            self.branch3x3dbl_3b(branch3x3dbl),
        ]
        branch3x3dbl = torch.cat(branch3x3dbl, 1)

        # Patch: The FID Inception model uses max pooling instead of average
        # pooling. This is likely an error in this specific Inception
        # implementation, as other Inception models use average pooling here
        # (which matches the description in the paper).
        branch_pool = F.max_pool2d(x, kernel_size=3, stride=1, padding=1)
        branch_pool = self.branch_pool(branch_pool)

        outputs = [branch1x1, branch3x3, branch3x3dbl, branch_pool]
        return torch.cat(outputs, 1)


def compute_val_fid(trainer, verbose=0):
    """
    Compute the fid score between the n=opts.train.fid.n_images real images
    from the validation set (domain is rf) and n fake images pained from
    those n validation images

    Args:
        trainer (climategan.Trainer): trainer to compute the val fid for

    Returns:
        float: FID score
    """
    # get opts params
    batch_size = trainer.opts.train.fid.get("batch_size", 50)
    dims = trainer.opts.train.fid.get("dims", 2048)

    # set inception model
    block_idx = InceptionV3.BLOCK_INDEX_BY_DIM[dims]
    model = InceptionV3([block_idx]).to(trainer.device)

    # first fid computation: compute the real stats, only once
    if trainer.real_val_fid_stats is None:
        if verbose > 0:
            print("Computing real_val_fid_stats for the first time")
        set_real_val_fid_stats(trainer, model, batch_size, dims)

    # get real stats
    real_m = trainer.real_val_fid_stats["m"]
    real_s = trainer.real_val_fid_stats["s"]

    # compute fake images
    fakes = compute_fakes(trainer)
    if verbose > 0:
        print("Computing fake activation statistics")
    # get fake stats
    fake_m, fake_s = calculate_activation_statistics(
        fakes, model, batch_size=batch_size, dims=dims, device=trainer.device
    )
    # compute FD between the real and the fake inception stats
    return calculate_frechet_distance(real_m, real_s, fake_m, fake_s)


def set_real_val_fid_stats(trainer, model, batch_size, dims):
    """
    Sets the real_val_fid_stats attribute of the trainer with the m and
    s outputs of calculate_activation_statistics on the real data.

    This needs to be done only once since nothing changes during training here.

    Args:
        trainer (climategan.Trainer): trainer instance to compute the stats for
        model (InceptionV3): inception model to get the activations from
        batch_size (int): inception inference batch size
        dims (int): dimension selected in the model
    """
    # in the rf domain display_size may be different from fid.n_images
    limit = trainer.opts.train.fid.n_images
    display_x = torch.stack(
        [sample["data"]["x"] for sample in trainer.display_images["val"]["rf"][:limit]]
    ).to(trainer.device)
    m, s = calculate_activation_statistics(
        display_x, model, batch_size=batch_size, dims=dims, device=trainer.device
    )
    trainer.real_val_fid_stats = {"m": m, "s": s}


def compute_fakes(trainer, verbose=0):
    """
    Compute current fake inferences

    Args:
        trainer (climategan.Trainer): trainer instance
        verbose (int, optional): Print level. Defaults to 0.

    Returns:
        torch.Tensor: trainer.opts.train.fid.n_images painted images
    """
    # in the rf domain display_size may be different from fid.n_images
    n = trainer.opts.train.fid.n_images
    bs = trainer.opts.data.loaders.batch_size

    display_batches = [
        (sample["data"]["x"], sample["data"]["m"])
        for sample in trainer.display_images["val"]["rf"][:n]
    ]

    display_x = torch.stack([b[0] for b in display_batches]).to(trainer.device)
    display_m = torch.stack([b[0] for b in display_batches]).to(trainer.device)
    nbs = len(display_x) // bs + 1

    fakes = []
    for b in range(nbs):
        if verbose > 0:
            print("computing fakes {}/{}".format(b + 1, nbs), end="\r", flush=True)
        with torch.no_grad():
            x = display_x[b * bs : (b + 1) * bs]
            m = display_m[b * bs : (b + 1) * bs]
            fake = trainer.G.paint(m, x)
        fakes.append(fake)

    return torch.cat(fakes, dim=0)


def calculate_activation_statistics(
    images, model, batch_size=50, dims=2048, device="cpu"
):
    """Calculation of the statistics used by the FID.
    Params:
    -- images       : List of images
    -- model       : Instance of inception model
    -- batch_size  : The images numpy array is split into batches with
                     batch size batch_size. A reasonable batch size
                     depends on the hardware.
    -- dims        : Dimensionality of features returned by Inception
    -- device      : Device to run calculations
    Returns:
    -- mu    : The mean over samples of the activations of the pool_3 layer of
               the inception model.
    -- sigma : The covariance matrix of the activations of the pool_3 layer of
               the inception model.
    """
    act = get_activations(images, model, batch_size, dims, device)
    mu = np.mean(act, axis=0)
    sigma = np.cov(act, rowvar=False)
    return mu, sigma


def get_activations(images, model, batch_size=50, dims=2048, device="cpu"):
    """Calculates the activations of the pool_3 layer for all images.
    Params:
    -- images       : List of images
    -- model       : Instance of inception model
    -- batch_size  : Batch size of images for the model to process at once.
                     Make sure that the number of samples is a multiple of
                     the batch size, otherwise some samples are ignored. This
                     behavior is retained to match the original FID score
                     implementation.
    -- dims        : Dimensionality of features returned by Inception
    -- device      : Device to run calculations
    Returns:
    -- A numpy array of dimension (num images, dims) that contains the
       activations of the given tensor when feeding inception with the
       query tensor.
    """
    model.eval()

    pred_arr = np.empty((len(images), dims))

    start_idx = 0
    nbs = len(images) // batch_size + 1

    for b in range(nbs):
        batch = images[b * batch_size : (b + 1) * batch_size].to(device)
        if not batch.nelement():
            continue

        with torch.no_grad():
            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))

        pred = pred.squeeze(3).squeeze(2).cpu().numpy()

        pred_arr[start_idx : start_idx + pred.shape[0]] = pred

        start_idx = start_idx + pred.shape[0]

    return pred_arr


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)).
    Stable version by Dougal J. Sutherland.
    Params:
    -- mu1   : Numpy array containing the activations of a layer of the
               inception net (like returned by the function 'get_predictions')
               for generated samples.
    -- mu2   : The sample mean over activations, precalculated on an
               representative data set.
    -- sigma1: The covariance matrix over activations for generated samples.
    -- sigma2: The covariance matrix over activations, precalculated on an
               representative data set.
    Returns:
    --   : The Frechet Distance.
    """

    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

    # 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
        print(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