# Copyright (c) 2022 Pablo Pernías MIT License
# Copyright 2024 UC Berkeley Team and 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.
# DISCLAIMER: This file is strongly influenced by https://github.com/ermongroup/ddim
import math
from dataclasses import dataclass
from typing import List, Optional, Tuple, Union
import torch
from ..configuration_utils import ConfigMixin, register_to_config
from ..utils import BaseOutput
from ..utils.torch_utils import randn_tensor
from .scheduling_utils import SchedulerMixin
@dataclass
class DDPMWuerstchenSchedulerOutput(BaseOutput):
"""
Output class for the scheduler's step function output.
Args:
prev_sample (`torch.Tensor` of shape `(batch_size, num_channels, height, width)` for images):
Computed sample (x_{t-1}) of previous timestep. `prev_sample` should be used as next model input in the
denoising loop.
"""
prev_sample: torch.Tensor
def betas_for_alpha_bar(
num_diffusion_timesteps,
max_beta=0.999,
alpha_transform_type="cosine",
):
"""
Create a beta schedule that discretizes the given alpha_t_bar function, which defines the cumulative product of
(1-beta) over time from t = [0,1].
Contains a function alpha_bar that takes an argument t and transforms it to the cumulative product of (1-beta) up
to that part of the diffusion process.
Args:
num_diffusion_timesteps (`int`): the number of betas to produce.
max_beta (`float`): the maximum beta to use; use values lower than 1 to
prevent singularities.
alpha_transform_type (`str`, *optional*, default to `cosine`): the type of noise schedule for alpha_bar.
Choose from `cosine` or `exp`
Returns:
betas (`np.ndarray`): the betas used by the scheduler to step the model outputs
"""
if alpha_transform_type == "cosine":
def alpha_bar_fn(t):
return math.cos((t + 0.008) / 1.008 * math.pi / 2) ** 2
elif alpha_transform_type == "exp":
def alpha_bar_fn(t):
return math.exp(t * -12.0)
else:
raise ValueError(f"Unsupported alpha_transform_type: {alpha_transform_type}")
betas = []
for i in range(num_diffusion_timesteps):
t1 = i / num_diffusion_timesteps
t2 = (i + 1) / num_diffusion_timesteps
betas.append(min(1 - alpha_bar_fn(t2) / alpha_bar_fn(t1), max_beta))
return torch.tensor(betas, dtype=torch.float32)
class DDPMWuerstchenScheduler(SchedulerMixin, ConfigMixin):
"""
Denoising diffusion probabilistic models (DDPMs) explores the connections between denoising score matching and
Langevin dynamics sampling.
[`~ConfigMixin`] takes care of storing all config attributes that are passed in the scheduler's `__init__`
function, such as `num_train_timesteps`. They can be accessed via `scheduler.config.num_train_timesteps`.
[`SchedulerMixin`] provides general loading and saving functionality via the [`SchedulerMixin.save_pretrained`] and
[`~SchedulerMixin.from_pretrained`] functions.
For more details, see the original paper: https://arxiv.org/abs/2006.11239
Args:
scaler (`float`): ....
s (`float`): ....
"""
@register_to_config
def __init__(
self,
scaler: float = 1.0,
s: float = 0.008,
):
self.scaler = scaler
self.s = torch.tensor([s])
self._init_alpha_cumprod = torch.cos(self.s / (1 + self.s) * torch.pi * 0.5) ** 2
# standard deviation of the initial noise distribution
self.init_noise_sigma = 1.0
def _alpha_cumprod(self, t, device):
if self.scaler > 1:
t = 1 - (1 - t) ** self.scaler
elif self.scaler < 1:
t = t**self.scaler
alpha_cumprod = torch.cos(
(t + self.s.to(device)) / (1 + self.s.to(device)) * torch.pi * 0.5
) ** 2 / self._init_alpha_cumprod.to(device)
return alpha_cumprod.clamp(0.0001, 0.9999)
def scale_model_input(self, sample: torch.Tensor, timestep: Optional[int] = None) -> torch.Tensor:
"""
Ensures interchangeability with schedulers that need to scale the denoising model input depending on the
current timestep.
Args:
sample (`torch.Tensor`): input sample
timestep (`int`, optional): current timestep
Returns:
`torch.Tensor`: scaled input sample
"""
return sample
def set_timesteps(
self,
num_inference_steps: int = None,
timesteps: Optional[List[int]] = None,
device: Union[str, torch.device] = None,
):
"""
Sets the discrete timesteps used for the diffusion chain. Supporting function to be run before inference.
Args:
num_inference_steps (`Dict[float, int]`):
the number of diffusion steps used when generating samples with a pre-trained model. If passed, then
`timesteps` must be `None`.
device (`str` or `torch.device`, optional):
the device to which the timesteps are moved to. {2 / 3: 20, 0.0: 10}
"""
if timesteps is None:
timesteps = torch.linspace(1.0, 0.0, num_inference_steps + 1, device=device)
if not isinstance(timesteps, torch.Tensor):
timesteps = torch.Tensor(timesteps).to(device)
self.timesteps = timesteps
def step(
self,
model_output: torch.Tensor,
timestep: int,
sample: torch.Tensor,
generator=None,
return_dict: bool = True,
) -> Union[DDPMWuerstchenSchedulerOutput, Tuple]:
"""
Predict the sample at the previous timestep by reversing the SDE. Core function to propagate the diffusion
process from the learned model outputs (most often the predicted noise).
Args:
model_output (`torch.Tensor`): direct output from learned diffusion model.
timestep (`int`): current discrete timestep in the diffusion chain.
sample (`torch.Tensor`):
current instance of sample being created by diffusion process.
generator: random number generator.
return_dict (`bool`): option for returning tuple rather than DDPMWuerstchenSchedulerOutput class
Returns:
[`DDPMWuerstchenSchedulerOutput`] or `tuple`: [`DDPMWuerstchenSchedulerOutput`] if `return_dict` is True,
otherwise a `tuple`. When returning a tuple, the first element is the sample tensor.
"""
dtype = model_output.dtype
device = model_output.device
t = timestep
prev_t = self.previous_timestep(t)
alpha_cumprod = self._alpha_cumprod(t, device).view(t.size(0), *[1 for _ in sample.shape[1:]])
alpha_cumprod_prev = self._alpha_cumprod(prev_t, device).view(prev_t.size(0), *[1 for _ in sample.shape[1:]])
alpha = alpha_cumprod / alpha_cumprod_prev
mu = (1.0 / alpha).sqrt() * (sample - (1 - alpha) * model_output / (1 - alpha_cumprod).sqrt())
std_noise = randn_tensor(mu.shape, generator=generator, device=model_output.device, dtype=model_output.dtype)
std = ((1 - alpha) * (1.0 - alpha_cumprod_prev) / (1.0 - alpha_cumprod)).sqrt() * std_noise
pred = mu + std * (prev_t != 0).float().view(prev_t.size(0), *[1 for _ in sample.shape[1:]])
if not return_dict:
return (pred.to(dtype),)
return DDPMWuerstchenSchedulerOutput(prev_sample=pred.to(dtype))
def add_noise(
self,
original_samples: torch.Tensor,
noise: torch.Tensor,
timesteps: torch.Tensor,
) -> torch.Tensor:
device = original_samples.device
dtype = original_samples.dtype
alpha_cumprod = self._alpha_cumprod(timesteps, device=device).view(
timesteps.size(0), *[1 for _ in original_samples.shape[1:]]
)
noisy_samples = alpha_cumprod.sqrt() * original_samples + (1 - alpha_cumprod).sqrt() * noise
return noisy_samples.to(dtype=dtype)
def __len__(self):
return self.config.num_train_timesteps
def previous_timestep(self, timestep):
index = (self.timesteps - timestep[0]).abs().argmin().item()
prev_t = self.timesteps[index + 1][None].expand(timestep.shape[0])
return prev_t