# Copyright 2023 Stanford University 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 code is strongly influenced by https://github.com/pesser/pytorch_diffusion # and https://github.com/hojonathanho/diffusion import math from dataclasses import dataclass from typing import List, Optional, Tuple, Union import numpy as np import torch from diffusers.configuration_utils import ConfigMixin, register_to_config from diffusers.utils import BaseOutput from diffusers.utils.torch_utils import randn_tensor from diffusers.schedulers.scheduling_utils import KarrasDiffusionSchedulers, SchedulerMixin class Time_Windows(): def __init__(self, t_initial=1, t_terminal=0, num_windows=4, precision=1./1000) -> None: assert t_terminal < t_initial time_windows = [ 1.*i/num_windows for i in range(1, num_windows+1)][::-1] self.window_starts = time_windows # [1.0, 0.75, 0.5, 0.25] self.window_ends = time_windows[1:] + [t_terminal] # [0.75, 0.5, 0.25, 0] self.precision = precision def get_window(self, tp): idx = 0 # robust to numerical error; e.g, (0.6+1/10000) belongs to [0.6, 0.3) while (tp-0.1*self.precision) <= self.window_ends[idx]: idx += 1 return self.window_starts[idx], self.window_ends[idx] def lookup_window(self, timepoint): if timepoint.dim() == 0: t_start, t_end = self.get_window(timepoint) t_start = torch.ones_like(timepoint) * t_start t_end = torch.ones_like(timepoint) * t_end else: t_start = torch.zeros_like(timepoint) t_end = torch.zeros_like(timepoint) bsz = timepoint.shape[0] for i in range(bsz): tp = timepoint[i] ts, te = self.get_window(tp) t_start[i] = ts t_end[i] = te return t_start, t_end @dataclass # Copied from diffusers.schedulers.scheduling_ddpm.DDPMSchedulerOutput with DDPM->DDIM class PeRFlowSchedulerOutput(BaseOutput): """ Output class for the scheduler's `step` function output. Args: prev_sample (`torch.FloatTensor` 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. pred_original_sample (`torch.FloatTensor` of shape `(batch_size, num_channels, height, width)` for images): The predicted denoised sample `(x_{0})` based on the model output from the current timestep. `pred_original_sample` can be used to preview progress or for guidance. """ prev_sample: torch.FloatTensor pred_original_sample: Optional[torch.FloatTensor] = None # Copied from diffusers.schedulers.scheduling_ddpm.betas_for_alpha_bar 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_tranform_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 PeRFlowScheduler(SchedulerMixin, ConfigMixin): """ `ReFlowScheduler` extends the denoising procedure introduced in denoising diffusion probabilistic models (DDPMs) with non-Markovian guidance. This model inherits from [`SchedulerMixin`] and [`ConfigMixin`]. Check the superclass documentation for the generic methods the library implements for all schedulers such as loading and saving. Args: num_train_timesteps (`int`, defaults to 1000): The number of diffusion steps to train the model. beta_start (`float`, defaults to 0.0001): The starting `beta` value of inference. beta_end (`float`, defaults to 0.02): The final `beta` value. beta_schedule (`str`, defaults to `"linear"`): The beta schedule, a mapping from a beta range to a sequence of betas for stepping the model. Choose from `linear`, `scaled_linear`, or `squaredcos_cap_v2`. trained_betas (`np.ndarray`, *optional*): Pass an array of betas directly to the constructor to bypass `beta_start` and `beta_end`. set_alpha_to_one (`bool`, defaults to `True`): Each diffusion step uses the alphas product value at that step and at the previous one. For the final step there is no previous alpha. When this option is `True` the previous alpha product is fixed to `1`, otherwise it uses the alpha value at step 0. prediction_type (`str`, defaults to `epsilon`, *optional*) """ _compatibles = [e.name for e in KarrasDiffusionSchedulers] order = 1 @register_to_config def __init__( self, num_train_timesteps: int = 1000, beta_start: float = 0.00085, beta_end: float = 0.012, beta_schedule: str = "scaled_linear", trained_betas: Optional[Union[np.ndarray, List[float]]] = None, set_alpha_to_one: bool = False, prediction_type: str = "epsilon", t_noise: float = 1, t_clean: float = 0, num_time_windows = 4, ): if trained_betas is not None: self.betas = torch.tensor(trained_betas, dtype=torch.float32) elif beta_schedule == "linear": self.betas = torch.linspace(beta_start, beta_end, num_train_timesteps, dtype=torch.float32) elif beta_schedule == "scaled_linear": # this schedule is very specific to the latent diffusion model. self.betas = torch.linspace(beta_start**0.5, beta_end**0.5, num_train_timesteps, dtype=torch.float32) ** 2 elif beta_schedule == "squaredcos_cap_v2": # Glide cosine schedule self.betas = betas_for_alpha_bar(num_train_timesteps) else: raise NotImplementedError(f"{beta_schedule} does is not implemented for {self.__class__}") self.alphas = 1.0 - self.betas self.alphas_cumprod = torch.cumprod(self.alphas, dim=0) # At every step in ddim, we are looking into the previous alphas_cumprod # For the final step, there is no previous alphas_cumprod because we are already at 0 # `set_alpha_to_one` decides whether we set this parameter simply to one or # whether we use the final alpha of the "non-previous" one. self.final_alpha_cumprod = torch.tensor(1.0) if set_alpha_to_one else self.alphas_cumprod[0] # # standard deviation of the initial noise distribution self.init_noise_sigma = 1.0 self.time_windows = Time_Windows(t_initial=t_noise, t_terminal=t_clean, num_windows=num_time_windows, precision=1./num_train_timesteps) def scale_model_input(self, sample: torch.FloatTensor, timestep: Optional[int] = None) -> torch.FloatTensor: """ Ensures interchangeability with schedulers that need to scale the denoising model input depending on the current timestep. Args: sample (`torch.FloatTensor`): The input sample. timestep (`int`, *optional*): The current timestep in the diffusion chain. Returns: `torch.FloatTensor`: A scaled input sample. """ return sample def set_timesteps(self, num_inference_steps: int, device: Union[str, torch.device] = None): """ Sets the discrete timesteps used for the diffusion chain (to be run before inference). Args: num_inference_steps (`int`): The number of diffusion steps used when generating samples with a pre-trained model. """ if num_inference_steps < self.config.num_time_windows: num_inference_steps = self.config.num_time_windows print(f"### We recommend a num_inference_steps not less than num_time_windows. It's set as {self.config.num_time_windows}.") timesteps = [] for i in range(self.config.num_time_windows): if i < num_inference_steps%self.config.num_time_windows: num_steps_cur_win = num_inference_steps//self.config.num_time_windows+1 else: num_steps_cur_win = num_inference_steps//self.config.num_time_windows t_s = self.time_windows.window_starts[i] t_e = self.time_windows.window_ends[i] timesteps_cur_win = np.linspace(t_s, t_e, num=num_steps_cur_win, endpoint=False) timesteps.append(timesteps_cur_win) timesteps = np.concatenate(timesteps) self.timesteps = torch.from_numpy( (timesteps*self.config.num_train_timesteps).astype(np.int64) ).to(device) def get_window_alpha(self, timestep): time_windows = self.time_windows num_train_timesteps = self.config.num_train_timesteps t_win_start, t_win_end = time_windows.lookup_window(timestep / num_train_timesteps) t_win_len = t_win_end - t_win_start t_interval = timestep / num_train_timesteps - t_win_start # NOTE: negative value idx_start = (t_win_start*num_train_timesteps - 1 ).long() idx_end = torch.clamp( (t_win_end*num_train_timesteps - 1 ).long(), min=0) alpha_cumprod_s_e = self.alphas_cumprod[idx_start] / self.alphas_cumprod[idx_end] gamma_s_e = alpha_cumprod_s_e ** 0.5 return t_win_start, t_win_end, t_win_len, t_interval, gamma_s_e def step( self, model_output: torch.FloatTensor, timestep: int, sample: torch.FloatTensor, return_dict: bool = True, ) -> Union[PeRFlowSchedulerOutput, Tuple]: """ Predict the sample from the previous timestep by reversing the SDE. This function propagates the diffusion process from the learned model outputs (most often the predicted noise). Args: model_output (`torch.FloatTensor`): The direct output from learned diffusion model. timestep (`float`): The current discrete timestep in the diffusion chain. sample (`torch.FloatTensor`): A current instance of a sample created by the diffusion process. return_dict (`bool`, *optional*, defaults to `True`): Whether or not to return a [`~schedulers.scheduling_ddim.PeRFlowSchedulerOutput`] or `tuple`. Returns: [`~schedulers.scheduling_utils.PeRFlowSchedulerOutput`] or `tuple`: If return_dict is `True`, [`~schedulers.scheduling_ddim.PeRFlowSchedulerOutput`] is returned, otherwise a tuple is returned where the first element is the sample tensor. """ if self.config.prediction_type == "epsilon": pred_epsilon = model_output t_win_start, t_win_end, t_win_len, t_interval, gamma_s_e = self.get_window_alpha(timestep) pred_sample_end = ( sample - (1-t_interval/t_win_len) * ((1-gamma_s_e**2)**0.5) * pred_epsilon ) \ / ( gamma_s_e + t_interval / t_win_len * (1-gamma_s_e) ) pred_velocity = (pred_sample_end - sample) / (t_win_end - (t_win_start + t_interval)) elif self.config.prediction_type == "velocity": pred_velocity = model_output else: raise ValueError( f"prediction_type given as {self.config.prediction_type} must be one of `epsilon` or `velocity`." ) # get dt idx = torch.argwhere(torch.where(self.timesteps==timestep, 1,0)) prev_step = self.timesteps[idx+1] if (idx+1) torch.FloatTensor: # Make sure alphas_cumprod and timestep have same device and dtype as original_samples alphas_cumprod = self.alphas_cumprod.to(device=original_samples.device, dtype=original_samples.dtype) timesteps = timesteps.to(original_samples.device) - 1 # indexing from 0 sqrt_alpha_prod = alphas_cumprod[timesteps] ** 0.5 sqrt_alpha_prod = sqrt_alpha_prod.flatten() while len(sqrt_alpha_prod.shape) < len(original_samples.shape): sqrt_alpha_prod = sqrt_alpha_prod.unsqueeze(-1) sqrt_one_minus_alpha_prod = (1 - alphas_cumprod[timesteps]) ** 0.5 sqrt_one_minus_alpha_prod = sqrt_one_minus_alpha_prod.flatten() while len(sqrt_one_minus_alpha_prod.shape) < len(original_samples.shape): sqrt_one_minus_alpha_prod = sqrt_one_minus_alpha_prod.unsqueeze(-1) noisy_samples = sqrt_alpha_prod * original_samples + sqrt_one_minus_alpha_prod * noise return noisy_samples def __len__(self): return self.config.num_train_timesteps