modeling_unet.py

# Copyright 2022 The HuggingFace Team. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and

# limitations under the License.

# helpers functions

import copy
import math
from functools import partial
from inspect import isfunction
from pathlib import Path

import torch
import torch.nn.functional as F
from torch import einsum, nn
from torch.cuda.amp import GradScaler, autocast
from torch.optim import Adam
from torch.utils import data

from einops import rearrange
from PIL import Image
from torchvision import transforms, utils
from tqdm import tqdm

from ...modeling_utils import PreTrainedModel
from .configuration_unet import UNetConfig


# NOTE: the following file is completely copied from https://github.com/lucidrains/denoising-diffusion-pytorch/blob/master/denoising_diffusion_pytorch/denoising_diffusion_pytorch.py





def exists(x):
    return x is not None


def default(val, d):
    if exists(val):
        return val
    return d() if isfunction(d) else d


def cycle(dl):
    while True:
        for data_dl in dl:
            yield data_dl


def num_to_groups(num, divisor):
    groups = num // divisor
    remainder = num % divisor
    arr = [divisor] * groups
    if remainder > 0:
        arr.append(remainder)
    return arr


def normalize_to_neg_one_to_one(img):
    return img * 2 - 1


def unnormalize_to_zero_to_one(t):
    return (t + 1) * 0.5


# small helper modules


class EMA:
    def __init__(self, beta):
        super().__init__()
        self.beta = beta

    def update_model_average(self, ma_model, current_model):
        for current_params, ma_params in zip(current_model.parameters(), ma_model.parameters()):
            old_weight, up_weight = ma_params.data, current_params.data
            ma_params.data = self.update_average(old_weight, up_weight)

    def update_average(self, old, new):
        if old is None:
            return new
        return old * self.beta + (1 - self.beta) * new


class Residual(nn.Module):
    def __init__(self, fn):
        super().__init__()
        self.fn = fn

    def forward(self, x, *args, **kwargs):
        return self.fn(x, *args, **kwargs) + x


class SinusoidalPosEmb(nn.Module):
    def __init__(self, dim):
        super().__init__()
        self.dim = dim

    def forward(self, x):
        device = x.device
        half_dim = self.dim // 2
        emb = math.log(10000) / (half_dim - 1)
        emb = torch.exp(torch.arange(half_dim, device=device) * -emb)
        emb = x[:, None] * emb[None, :]
        emb = torch.cat((emb.sin(), emb.cos()), dim=-1)
        return emb


def Upsample(dim):
    return nn.ConvTranspose2d(dim, dim, 4, 2, 1)


def Downsample(dim):
    return nn.Conv2d(dim, dim, 4, 2, 1)


class LayerNorm(nn.Module):
    def __init__(self, dim, eps=1e-5):
        super().__init__()
        self.eps = eps
        self.g = nn.Parameter(torch.ones(1, dim, 1, 1))
        self.b = nn.Parameter(torch.zeros(1, dim, 1, 1))

    def forward(self, x):
        var = torch.var(x, dim=1, unbiased=False, keepdim=True)
        mean = torch.mean(x, dim=1, keepdim=True)
        return (x - mean) / (var + self.eps).sqrt() * self.g + self.b


class PreNorm(nn.Module):
    def __init__(self, dim, fn):
        super().__init__()
        self.fn = fn
        self.norm = LayerNorm(dim)

    def forward(self, x):
        x = self.norm(x)
        return self.fn(x)


# building block modules


class Block(nn.Module):
    def __init__(self, dim, dim_out, groups=8):
        super().__init__()
        self.proj = nn.Conv2d(dim, dim_out, 3, padding=1)
        self.norm = nn.GroupNorm(groups, dim_out)
        self.act = nn.SiLU()

    def forward(self, x, scale_shift=None):
        x = self.proj(x)
        x = self.norm(x)

        if exists(scale_shift):
            scale, shift = scale_shift
            x = x * (scale + 1) + shift

        x = self.act(x)
        return x


class ResnetBlock(nn.Module):
    def __init__(self, dim, dim_out, *, time_emb_dim=None, groups=8):
        super().__init__()
        self.mlp = nn.Sequential(nn.SiLU(), nn.Linear(time_emb_dim, dim_out * 2)) if exists(time_emb_dim) else None

        self.block1 = Block(dim, dim_out, groups=groups)
        self.block2 = Block(dim_out, dim_out, groups=groups)
        self.res_conv = nn.Conv2d(dim, dim_out, 1) if dim != dim_out else nn.Identity()

    def forward(self, x, time_emb=None):

        scale_shift = None
        if exists(self.mlp) and exists(time_emb):
            time_emb = self.mlp(time_emb)
            time_emb = rearrange(time_emb, "b c -> b c 1 1")
            scale_shift = time_emb.chunk(2, dim=1)

        h = self.block1(x, scale_shift=scale_shift)

        h = self.block2(h)
        return h + self.res_conv(x)


class LinearAttention(nn.Module):
    def __init__(self, dim, heads=4, dim_head=32):
        super().__init__()
        self.scale = dim_head**-0.5
        self.heads = heads
        hidden_dim = dim_head * heads
        self.to_qkv = nn.Conv2d(dim, hidden_dim * 3, 1, bias=False)

        self.to_out = nn.Sequential(nn.Conv2d(hidden_dim, dim, 1), LayerNorm(dim))

    def forward(self, x):
        b, c, h, w = x.shape
        qkv = self.to_qkv(x).chunk(3, dim=1)
        q, k, v = map(lambda t: rearrange(t, "b (h c) x y -> b h c (x y)", h=self.heads), qkv)

        q = q.softmax(dim=-2)
        k = k.softmax(dim=-1)

        q = q * self.scale
        context = torch.einsum("b h d n, b h e n -> b h d e", k, v)

        out = torch.einsum("b h d e, b h d n -> b h e n", context, q)
        out = rearrange(out, "b h c (x y) -> b (h c) x y", h=self.heads, x=h, y=w)
        return self.to_out(out)


class Attention(nn.Module):
    def __init__(self, dim, heads=4, dim_head=32):
        super().__init__()
        self.scale = dim_head**-0.5
        self.heads = heads
        hidden_dim = dim_head * heads
        self.to_qkv = nn.Conv2d(dim, hidden_dim * 3, 1, bias=False)
        self.to_out = nn.Conv2d(hidden_dim, dim, 1)

    def forward(self, x):
        b, c, h, w = x.shape
        qkv = self.to_qkv(x).chunk(3, dim=1)
        q, k, v = map(lambda t: rearrange(t, "b (h c) x y -> b h c (x y)", h=self.heads), qkv)
        q = q * self.scale

        sim = einsum("b h d i, b h d j -> b h i j", q, k)
        sim = sim - sim.amax(dim=-1, keepdim=True).detach()
        attn = sim.softmax(dim=-1)

        out = einsum("b h i j, b h d j -> b h i d", attn, v)
        out = rearrange(out, "b h (x y) d -> b (h d) x y", x=h, y=w)
        return self.to_out(out)


class UNetModel(PreTrainedModel):

    config_class = UNetConfig

    def __init__(self, config):
        super().__init__(config)

        init_dim = None
        out_dim = None
        channels = 3
        with_time_emb = True
        resnet_block_groups = 8
        learned_variance = False

        # determine dimensions

        dim_mults = config.dim_mults
        dim = config.dim
        self.channels = config.channels

        init_dim = default(init_dim, dim // 3 * 2)
        self.init_conv = nn.Conv2d(channels, init_dim, 7, padding=3)

        dims = [init_dim, *map(lambda m: dim * m, dim_mults)]
        in_out = list(zip(dims[:-1], dims[1:]))

        block_klass = partial(ResnetBlock, groups=resnet_block_groups)

        # time embeddings

        if with_time_emb:
            time_dim = dim * 4
            self.time_mlp = nn.Sequential(
                SinusoidalPosEmb(dim), nn.Linear(dim, time_dim), nn.GELU(), nn.Linear(time_dim, time_dim)
            )
        else:
            time_dim = None
            self.time_mlp = None

        # layers

        self.downs = nn.ModuleList([])
        self.ups = nn.ModuleList([])
        num_resolutions = len(in_out)

        for ind, (dim_in, dim_out) in enumerate(in_out):
            is_last = ind >= (num_resolutions - 1)

            self.downs.append(
                nn.ModuleList(
                    [
                        block_klass(dim_in, dim_out, time_emb_dim=time_dim),
                        block_klass(dim_out, dim_out, time_emb_dim=time_dim),
                        Residual(PreNorm(dim_out, LinearAttention(dim_out))),
                        Downsample(dim_out) if not is_last else nn.Identity(),
                    ]
                )
            )

        mid_dim = dims[-1]
        self.mid_block1 = block_klass(mid_dim, mid_dim, time_emb_dim=time_dim)
        self.mid_attn = Residual(PreNorm(mid_dim, Attention(mid_dim)))
        self.mid_block2 = block_klass(mid_dim, mid_dim, time_emb_dim=time_dim)

        for ind, (dim_in, dim_out) in enumerate(reversed(in_out[1:])):
            is_last = ind >= (num_resolutions - 1)

            self.ups.append(
                nn.ModuleList(
                    [
                        block_klass(dim_out * 2, dim_in, time_emb_dim=time_dim),
                        block_klass(dim_in, dim_in, time_emb_dim=time_dim),
                        Residual(PreNorm(dim_in, LinearAttention(dim_in))),
                        Upsample(dim_in) if not is_last else nn.Identity(),
                    ]
                )
            )

        default_out_dim = channels * (1 if not learned_variance else 2)
        self.out_dim = default(out_dim, default_out_dim)

        self.final_conv = nn.Sequential(block_klass(dim, dim), nn.Conv2d(dim, self.out_dim, 1))

    def forward(self, x, time):
        x = self.init_conv(x)

        t = self.time_mlp(time) if exists(self.time_mlp) else None

        h = []

        for block1, block2, attn, downsample in self.downs:
            x = block1(x, t)
            x = block2(x, t)
            x = attn(x)
            h.append(x)
            x = downsample(x)

        x = self.mid_block1(x, t)
        x = self.mid_attn(x)
        x = self.mid_block2(x, t)

        for block1, block2, attn, upsample in self.ups:
            x = torch.cat((x, h.pop()), dim=1)
            x = block1(x, t)
            x = block2(x, t)
            x = attn(x)
            x = upsample(x)

        return self.final_conv(x)


# gaussian diffusion trainer class


def extract(a, t, x_shape):
    b, *_ = t.shape
    out = a.gather(-1, t)
    return out.reshape(b, *((1,) * (len(x_shape) - 1)))


def noise_like(shape, device, repeat=False):
    def repeat_noise():
        return torch.randn((1, *shape[1:]), device=device).repeat(shape[0], *((1,) * (len(shape) - 1)))

    def noise():
        return torch.randn(shape, device=device)

    return repeat_noise() if repeat else noise()


def linear_beta_schedule(timesteps):
    scale = 1000 / timesteps
    beta_start = scale * 0.0001
    beta_end = scale * 0.02
    return torch.linspace(beta_start, beta_end, timesteps, dtype=torch.float64)


def cosine_beta_schedule(timesteps, s=0.008):
    """
    cosine schedule
    as proposed in https://openreview.net/forum?id=-NEXDKk8gZ
    """
    steps = timesteps + 1
    x = torch.linspace(0, timesteps, steps, dtype=torch.float64)
    alphas_cumprod = torch.cos(((x / timesteps) + s) / (1 + s) * torch.pi * 0.5) ** 2
    alphas_cumprod = alphas_cumprod / alphas_cumprod[0]
    betas = 1 - (alphas_cumprod[1:] / alphas_cumprod[:-1])
    return torch.clip(betas, 0, 0.999)


class GaussianDiffusion(nn.Module):
    def __init__(
        self,
        denoise_fn,
        *,
        image_size,
        channels=3,
        timesteps=1000,
        loss_type="l1",
        objective="pred_noise",
        beta_schedule="cosine",
    ):
        super().__init__()
        assert not (type(self) == GaussianDiffusion and denoise_fn.channels != denoise_fn.out_dim)

        self.channels = channels
        self.image_size = image_size
        self.denoise_fn = denoise_fn
        self.objective = objective

        if beta_schedule == "linear":
            betas = linear_beta_schedule(timesteps)
        elif beta_schedule == "cosine":
            betas = cosine_beta_schedule(timesteps)
        else:
            raise ValueError(f"unknown beta schedule {beta_schedule}")

        alphas = 1.0 - betas
        alphas_cumprod = torch.cumprod(alphas, axis=0)
        alphas_cumprod_prev = F.pad(alphas_cumprod[:-1], (1, 0), value=1.0)

        (timesteps,) = betas.shape
        self.num_timesteps = int(timesteps)
        self.loss_type = loss_type

        # helper function to register buffer from float64 to float32

        def register_buffer(name, val):
            self.register_buffer(name, val.to(torch.float32))

        register_buffer("betas", betas)
        register_buffer("alphas_cumprod", alphas_cumprod)
        register_buffer("alphas_cumprod_prev", alphas_cumprod_prev)

        # calculations for diffusion q(x_t | x_{t-1}) and others

        register_buffer("sqrt_alphas_cumprod", torch.sqrt(alphas_cumprod))
        register_buffer("sqrt_one_minus_alphas_cumprod", torch.sqrt(1.0 - alphas_cumprod))
        register_buffer("log_one_minus_alphas_cumprod", torch.log(1.0 - alphas_cumprod))
        register_buffer("sqrt_recip_alphas_cumprod", torch.sqrt(1.0 / alphas_cumprod))
        register_buffer("sqrt_recipm1_alphas_cumprod", torch.sqrt(1.0 / alphas_cumprod - 1))

        # calculations for posterior q(x_{t-1} | x_t, x_0)

        posterior_variance = betas * (1.0 - alphas_cumprod_prev) / (1.0 - alphas_cumprod)

        # above: equal to 1. / (1. / (1. - alpha_cumprod_tm1) + alpha_t / beta_t)

        register_buffer("posterior_variance", posterior_variance)

        # below: log calculation clipped because the posterior variance is 0 at the beginning of the diffusion chain

        register_buffer("posterior_log_variance_clipped", torch.log(posterior_variance.clamp(min=1e-20)))
        register_buffer("posterior_mean_coef1", betas * torch.sqrt(alphas_cumprod_prev) / (1.0 - alphas_cumprod))
        register_buffer(
            "posterior_mean_coef2", (1.0 - alphas_cumprod_prev) * torch.sqrt(alphas) / (1.0 - alphas_cumprod)
        )

    def predict_start_from_noise(self, x_t, t, noise):
        return (
            extract(self.sqrt_recip_alphas_cumprod, t, x_t.shape) * x_t
            - extract(self.sqrt_recipm1_alphas_cumprod, t, x_t.shape) * noise
        )

    def q_posterior(self, x_start, x_t, t):
        posterior_mean = (
            extract(self.posterior_mean_coef1, t, x_t.shape) * x_start
            + extract(self.posterior_mean_coef2, t, x_t.shape) * x_t
        )
        posterior_variance = extract(self.posterior_variance, t, x_t.shape)
        posterior_log_variance_clipped = extract(self.posterior_log_variance_clipped, t, x_t.shape)
        return posterior_mean, posterior_variance, posterior_log_variance_clipped

    def p_mean_variance(self, x, t, clip_denoised: bool):
        model_output = self.denoise_fn(x, t)

        if self.objective == "pred_noise":
            x_start = self.predict_start_from_noise(x, t=t, noise=model_output)
        elif self.objective == "pred_x0":
            x_start = model_output
        else:
            raise ValueError(f"unknown objective {self.objective}")

        if clip_denoised:
            x_start.clamp_(-1.0, 1.0)

        model_mean, posterior_variance, posterior_log_variance = self.q_posterior(x_start=x_start, x_t=x, t=t)
        return model_mean, posterior_variance, posterior_log_variance

    @torch.no_grad()
    def p_sample(self, x, t, clip_denoised=True, repeat_noise=False):
        b, *_, device = *x.shape, x.device
        model_mean, _, model_log_variance = self.p_mean_variance(x=x, t=t, clip_denoised=clip_denoised)
        noise = noise_like(x.shape, device, repeat_noise)
        # no noise when t == 0
        nonzero_mask = (1 - (t == 0).float()).reshape(b, *((1,) * (len(x.shape) - 1)))
        result = model_mean + nonzero_mask * (0.5 * model_log_variance).exp() * noise
        return result

    @torch.no_grad()
    def p_sample_loop(self, shape):
        device = self.betas.device

        b = shape[0]
        img = torch.randn(shape, device=device)

        for i in tqdm(
            reversed(range(0, self.num_timesteps)), desc="sampling loop time step", total=self.num_timesteps
        ):
            img = self.p_sample(img, torch.full((b,), i, device=device, dtype=torch.long))

        img = unnormalize_to_zero_to_one(img)
        return img

    @torch.no_grad()
    def sample(self, batch_size=16):
        image_size = self.image_size
        channels = self.channels
        return self.p_sample_loop((batch_size, channels, image_size, image_size))

    @torch.no_grad()
    def interpolate(self, x1, x2, t=None, lam=0.5):
        b, *_, device = *x1.shape, x1.device
        t = default(t, self.num_timesteps - 1)

        assert x1.shape == x2.shape

        t_batched = torch.stack([torch.tensor(t, device=device)] * b)
        xt1, xt2 = map(lambda x: self.q_sample(x, t=t_batched), (x1, x2))

        img = (1 - lam) * xt1 + lam * xt2
        for i in tqdm(reversed(range(0, t)), desc="interpolation sample time step", total=t):
            img = self.p_sample(img, torch.full((b,), i, device=device, dtype=torch.long))

        return img

    def q_sample(self, x_start, t, noise=None):
        noise = default(noise, lambda: torch.randn_like(x_start))

        return (
            extract(self.sqrt_alphas_cumprod, t, x_start.shape) * x_start
            + extract(self.sqrt_one_minus_alphas_cumprod, t, x_start.shape) * noise
        )

    @property
    def loss_fn(self):
        if self.loss_type == "l1":
            return F.l1_loss
        elif self.loss_type == "l2":
            return F.mse_loss
        else:
            raise ValueError(f"invalid loss type {self.loss_type}")

    def p_losses(self, x_start, t, noise=None):
        b, c, h, w = x_start.shape
        noise = default(noise, lambda: torch.randn_like(x_start))

        x = self.q_sample(x_start=x_start, t=t, noise=noise)
        model_out = self.denoise_fn(x, t)

        if self.objective == "pred_noise":
            target = noise
        elif self.objective == "pred_x0":
            target = x_start
        else:
            raise ValueError(f"unknown objective {self.objective}")

        loss = self.loss_fn(model_out, target)
        return loss

    def forward(self, img, *args, **kwargs):
        b, _, h, w, device, img_size, = (
            *img.shape,
            img.device,
            self.image_size,
        )
        assert h == img_size and w == img_size, f"height and width of image must be {img_size}"
        t = torch.randint(0, self.num_timesteps, (b,), device=device).long()

        img = normalize_to_neg_one_to_one(img)
        return self.p_losses(img, t, *args, **kwargs)


# dataset classes


class Dataset(data.Dataset):
    def __init__(self, folder, image_size, exts=["jpg", "jpeg", "png"]):
        super().__init__()
        self.folder = folder
        self.image_size = image_size
        self.paths = [p for ext in exts for p in Path(f"{folder}").glob(f"**/*.{ext}")]

        self.transform = transforms.Compose(
            [
                transforms.Resize(image_size),
                transforms.RandomHorizontalFlip(),
                transforms.CenterCrop(image_size),
                transforms.ToTensor(),
            ]
        )

    def __len__(self):
        return len(self.paths)

    def __getitem__(self, index):
        path = self.paths[index]
        img = Image.open(path)
        return self.transform(img)


# trainer class


class Trainer(object):
    def __init__(
        self,
        diffusion_model,
        folder,
        *,
        ema_decay=0.995,
        image_size=128,
        train_batch_size=32,
        train_lr=1e-4,
        train_num_steps=100000,
        gradient_accumulate_every=2,
        amp=False,
        step_start_ema=2000,
        update_ema_every=10,
        save_and_sample_every=1000,
        results_folder="./results",
    ):
        super().__init__()
        self.model = diffusion_model
        self.ema = EMA(ema_decay)
        self.ema_model = copy.deepcopy(self.model)
        self.update_ema_every = update_ema_every

        self.step_start_ema = step_start_ema
        self.save_and_sample_every = save_and_sample_every

        self.batch_size = train_batch_size
        self.image_size = diffusion_model.image_size
        self.gradient_accumulate_every = gradient_accumulate_every
        self.train_num_steps = train_num_steps

        self.ds = Dataset(folder, image_size)
        self.dl = cycle(data.DataLoader(self.ds, batch_size=train_batch_size, shuffle=True, pin_memory=True))
        self.opt = Adam(diffusion_model.parameters(), lr=train_lr)

        self.step = 0

        self.amp = amp
        self.scaler = GradScaler(enabled=amp)

        self.results_folder = Path(results_folder)
        self.results_folder.mkdir(exist_ok=True)

        self.reset_parameters()

    def reset_parameters(self):
        self.ema_model.load_state_dict(self.model.state_dict())

    def step_ema(self):
        if self.step < self.step_start_ema:
            self.reset_parameters()
            return
        self.ema.update_model_average(self.ema_model, self.model)

    def save(self, milestone):
        data = {
            "step": self.step,
            "model": self.model.state_dict(),
            "ema": self.ema_model.state_dict(),
            "scaler": self.scaler.state_dict(),
        }
        torch.save(data, str(self.results_folder / f"model-{milestone}.pt"))

    def load(self, milestone):
        data = torch.load(str(self.results_folder / f"model-{milestone}.pt"))

        self.step = data["step"]
        self.model.load_state_dict(data["model"])
        self.ema_model.load_state_dict(data["ema"])
        self.scaler.load_state_dict(data["scaler"])

    def train(self):
        with tqdm(initial=self.step, total=self.train_num_steps) as pbar:

            while self.step < self.train_num_steps:
                for i in range(self.gradient_accumulate_every):
                    data = next(self.dl).cuda()

                    with autocast(enabled=self.amp):
                        loss = self.model(data)
                        self.scaler.scale(loss / self.gradient_accumulate_every).backward()

                    pbar.set_description(f"loss: {loss.item():.4f}")

                self.scaler.step(self.opt)
                self.scaler.update()
                self.opt.zero_grad()

                if self.step % self.update_ema_every == 0:
                    self.step_ema()

                if self.step != 0 and self.step % self.save_and_sample_every == 0:
                    self.ema_model.eval()

                    milestone = self.step // self.save_and_sample_every
                    batches = num_to_groups(36, self.batch_size)
                    all_images_list = list(map(lambda n: self.ema_model.sample(batch_size=n), batches))
                    all_images = torch.cat(all_images_list, dim=0)
                    utils.save_image(all_images, str(self.results_folder / f"sample-{milestone}.png"), nrow=6)
                    self.save(milestone)

                self.step += 1
                pbar.update(1)

        print("training complete")