from dataclasses import dataclass from typing import Optional, Tuple, Union, List import math import numpy as np import torch from diffusers.configuration_utils import ConfigMixin, register_to_config from diffusers.utils import BaseOutput, logging from diffusers.utils.torch_utils import randn_tensor from diffusers.schedulers.scheduling_utils import SchedulerMixin @dataclass class FlowMatchEulerDiscreteSchedulerOutput(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. """ prev_sample: torch.FloatTensor class PyramidFlowMatchEulerDiscreteScheduler(SchedulerMixin, ConfigMixin): """ Euler scheduler. 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. timestep_spacing (`str`, defaults to `"linspace"`): The way the timesteps should be scaled. Refer to Table 2 of the [Common Diffusion Noise Schedules and Sample Steps are Flawed](https://huggingface.co/papers/2305.08891) for more information. shift (`float`, defaults to 1.0): The shift value for the timestep schedule. """ _compatibles = [] order = 1 @register_to_config def __init__( self, num_train_timesteps: int = 1000, shift: float = 1.0, # Following Stable diffusion 3, stages: int = 3, stage_range: List = [0, 1/3, 2/3, 1], gamma: float = 1/3, ): self.timestep_ratios = {} # The timestep ratio for each stage self.timesteps_per_stage = {} # The detailed timesteps per stage self.sigmas_per_stage = {} self.start_sigmas = {} self.end_sigmas = {} self.ori_start_sigmas = {} # self.init_sigmas() self.init_sigmas_for_each_stage() self.sigma_min = self.sigmas[-1].item() self.sigma_max = self.sigmas[0].item() self.gamma = gamma def init_sigmas(self): """ initialize the global timesteps and sigmas """ num_train_timesteps = self.config.num_train_timesteps shift = self.config.shift timesteps = np.linspace(1, num_train_timesteps, num_train_timesteps, dtype=np.float32)[::-1].copy() timesteps = torch.from_numpy(timesteps).to(dtype=torch.float32) sigmas = timesteps / num_train_timesteps sigmas = shift * sigmas / (1 + (shift - 1) * sigmas) self.timesteps = sigmas * num_train_timesteps self._step_index = None self._begin_index = None self.sigmas = sigmas.to("cpu") # to avoid too much CPU/GPU communication def init_sigmas_for_each_stage(self): """ Init the timesteps for each stage """ self.init_sigmas() stage_distance = [] stages = self.config.stages training_steps = self.config.num_train_timesteps stage_range = self.config.stage_range # Init the start and end point of each stage for i_s in range(stages): # To decide the start and ends point start_indice = int(stage_range[i_s] * training_steps) start_indice = max(start_indice, 0) end_indice = int(stage_range[i_s+1] * training_steps) end_indice = min(end_indice, training_steps) start_sigma = self.sigmas[start_indice].item() end_sigma = self.sigmas[end_indice].item() if end_indice < training_steps else 0.0 self.ori_start_sigmas[i_s] = start_sigma if i_s != 0: ori_sigma = 1 - start_sigma gamma = self.config.gamma corrected_sigma = (1 / (math.sqrt(1 + (1 / gamma)) * (1 - ori_sigma) + ori_sigma)) * ori_sigma # corrected_sigma = 1 / (2 - ori_sigma) * ori_sigma start_sigma = 1 - corrected_sigma stage_distance.append(start_sigma - end_sigma) self.start_sigmas[i_s] = start_sigma self.end_sigmas[i_s] = end_sigma # Determine the ratio of each stage according to flow length tot_distance = sum(stage_distance) for i_s in range(stages): if i_s == 0: start_ratio = 0.0 else: start_ratio = sum(stage_distance[:i_s]) / tot_distance if i_s == stages - 1: end_ratio = 1.0 else: end_ratio = sum(stage_distance[:i_s+1]) / tot_distance self.timestep_ratios[i_s] = (start_ratio, end_ratio) # Determine the timesteps and sigmas for each stage for i_s in range(stages): timestep_ratio = self.timestep_ratios[i_s] timestep_max = self.timesteps[int(timestep_ratio[0] * training_steps)] timestep_min = self.timesteps[min(int(timestep_ratio[1] * training_steps), training_steps - 1)] timesteps = np.linspace( timestep_max, timestep_min, training_steps + 1, ) self.timesteps_per_stage[i_s] = timesteps[:-1] if isinstance(timesteps, torch.Tensor) else torch.from_numpy(timesteps[:-1]) stage_sigmas = np.linspace( 1, 0, training_steps + 1, ) self.sigmas_per_stage[i_s] = torch.from_numpy(stage_sigmas[:-1]) @property def step_index(self): """ The index counter for current timestep. It will increase 1 after each scheduler step. """ return self._step_index @property def begin_index(self): """ The index for the first timestep. It should be set from pipeline with `set_begin_index` method. """ return self._begin_index # Copied from diffusers.schedulers.scheduling_dpmsolver_multistep.DPMSolverMultistepScheduler.set_begin_index def set_begin_index(self, begin_index: int = 0): """ Sets the begin index for the scheduler. This function should be run from pipeline before the inference. Args: begin_index (`int`): The begin index for the scheduler. """ self._begin_index = begin_index def _sigma_to_t(self, sigma): return sigma * self.config.num_train_timesteps def set_timesteps(self, num_inference_steps: int, stage_index: int, device: Union[str, torch.device] = None): """ Setting the timesteps and sigmas for each stage """ self.num_inference_steps = num_inference_steps training_steps = self.config.num_train_timesteps self.init_sigmas() stage_timesteps = self.timesteps_per_stage[stage_index] timestep_max = stage_timesteps[0].item() timestep_min = stage_timesteps[-1].item() timesteps = np.linspace( timestep_max, timestep_min, num_inference_steps, ) self.timesteps = torch.from_numpy(timesteps).to(device=device) stage_sigmas = self.sigmas_per_stage[stage_index] sigma_max = stage_sigmas[0].item() sigma_min = stage_sigmas[-1].item() ratios = np.linspace( sigma_max, sigma_min, num_inference_steps ) sigmas = torch.from_numpy(ratios).to(device=device) self.sigmas = torch.cat([sigmas, torch.zeros(1, device=sigmas.device)]) self._step_index = None def index_for_timestep(self, timestep, schedule_timesteps=None): if schedule_timesteps is None: schedule_timesteps = self.timesteps indices = (schedule_timesteps == timestep).nonzero() # The sigma index that is taken for the **very** first `step` # is always the second index (or the last index if there is only 1) # This way we can ensure we don't accidentally skip a sigma in # case we start in the middle of the denoising schedule (e.g. for image-to-image) pos = 1 if len(indices) > 1 else 0 return indices[pos].item() def _init_step_index(self, timestep): if self.begin_index is None: if isinstance(timestep, torch.Tensor): timestep = timestep.to(self.timesteps.device) self._step_index = self.index_for_timestep(timestep) else: self._step_index = self._begin_index def step( self, model_output: torch.FloatTensor, timestep: Union[float, torch.FloatTensor], sample: torch.FloatTensor, generator: Optional[torch.Generator] = None, return_dict: bool = True, ) -> Union[FlowMatchEulerDiscreteSchedulerOutput, 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. generator (`torch.Generator`, *optional*): A random number generator. return_dict (`bool`): Whether or not to return a [`~schedulers.scheduling_euler_discrete.EulerDiscreteSchedulerOutput`] or tuple. Returns: [`~schedulers.scheduling_euler_discrete.EulerDiscreteSchedulerOutput`] or `tuple`: If return_dict is `True`, [`~schedulers.scheduling_euler_discrete.EulerDiscreteSchedulerOutput`] is returned, otherwise a tuple is returned where the first element is the sample tensor. """ if ( isinstance(timestep, int) or isinstance(timestep, torch.IntTensor) or isinstance(timestep, torch.LongTensor) ): raise ValueError( ( "Passing integer indices (e.g. from `enumerate(timesteps)`) as timesteps to" " `EulerDiscreteScheduler.step()` is not supported. Make sure to pass" " one of the `scheduler.timesteps` as a timestep." ), ) if self.step_index is None: self._step_index = 0 # Upcast to avoid precision issues when computing prev_sample sample = sample.to(torch.float32) sigma = self.sigmas[self.step_index] sigma_next = self.sigmas[self.step_index + 1] prev_sample = sample + (sigma_next - sigma) * model_output # Cast sample back to model compatible dtype prev_sample = prev_sample.to(model_output.dtype) # upon completion increase step index by one self._step_index += 1 if not return_dict: return (prev_sample,) return FlowMatchEulerDiscreteSchedulerOutput(prev_sample=prev_sample) def __len__(self): return self.config.num_train_timesteps