# Copyright 2022 NVIDIA 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. from dataclasses import dataclass from typing import Optional, Tuple, Union import flax import jax.numpy as jnp from jax import random from ..configuration_utils import ConfigMixin, register_to_config from ..utils import BaseOutput from .scheduling_utils_flax import FlaxSchedulerMixin @flax.struct.dataclass class KarrasVeSchedulerState: # setable values num_inference_steps: Optional[int] = None timesteps: Optional[jnp.ndarray] = None schedule: Optional[jnp.ndarray] = None # sigma(t_i) @classmethod def create(cls): return cls() @dataclass class FlaxKarrasVeOutput(BaseOutput): """ Output class for the scheduler's step function output. Args: prev_sample (`jnp.ndarray` 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. derivative (`jnp.ndarray` of shape `(batch_size, num_channels, height, width)` for images): Derivative of predicted original image sample (x_0). state (`KarrasVeSchedulerState`): the `FlaxKarrasVeScheduler` state data class. """ prev_sample: jnp.ndarray derivative: jnp.ndarray state: KarrasVeSchedulerState class FlaxKarrasVeScheduler(FlaxSchedulerMixin, ConfigMixin): """ Stochastic sampling from Karras et al. [1] tailored to the Variance-Expanding (VE) models [2]. Use Algorithm 2 and the VE column of Table 1 from [1] for reference. [1] Karras, Tero, et al. "Elucidating the Design Space of Diffusion-Based Generative Models." https://arxiv.org/abs/2206.00364 [2] Song, Yang, et al. "Score-based generative modeling through stochastic differential equations." https://arxiv.org/abs/2011.13456 [`~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 on the parameters, see the original paper's Appendix E.: "Elucidating the Design Space of Diffusion-Based Generative Models." https://arxiv.org/abs/2206.00364. The grid search values used to find the optimal {s_noise, s_churn, s_min, s_max} for a specific model are described in Table 5 of the paper. Args: sigma_min (`float`): minimum noise magnitude sigma_max (`float`): maximum noise magnitude s_noise (`float`): the amount of additional noise to counteract loss of detail during sampling. A reasonable range is [1.000, 1.011]. s_churn (`float`): the parameter controlling the overall amount of stochasticity. A reasonable range is [0, 100]. s_min (`float`): the start value of the sigma range where we add noise (enable stochasticity). A reasonable range is [0, 10]. s_max (`float`): the end value of the sigma range where we add noise. A reasonable range is [0.2, 80]. """ @property def has_state(self): return True @register_to_config def __init__( self, sigma_min: float = 0.02, sigma_max: float = 100, s_noise: float = 1.007, s_churn: float = 80, s_min: float = 0.05, s_max: float = 50, ): pass def create_state(self): return KarrasVeSchedulerState.create() def set_timesteps( self, state: KarrasVeSchedulerState, num_inference_steps: int, shape: Tuple = () ) -> KarrasVeSchedulerState: """ Sets the continuous timesteps used for the diffusion chain. Supporting function to be run before inference. Args: state (`KarrasVeSchedulerState`): the `FlaxKarrasVeScheduler` state data class. num_inference_steps (`int`): the number of diffusion steps used when generating samples with a pre-trained model. """ timesteps = jnp.arange(0, num_inference_steps)[::-1].copy() schedule = [ ( self.config.sigma_max**2 * (self.config.sigma_min**2 / self.config.sigma_max**2) ** (i / (num_inference_steps - 1)) ) for i in timesteps ] return state.replace( num_inference_steps=num_inference_steps, schedule=jnp.array(schedule, dtype=jnp.float32), timesteps=timesteps, ) def add_noise_to_input( self, state: KarrasVeSchedulerState, sample: jnp.ndarray, sigma: float, key: random.KeyArray, ) -> Tuple[jnp.ndarray, float]: """ Explicit Langevin-like "churn" step of adding noise to the sample according to a factor gamma_i ≥ 0 to reach a higher noise level sigma_hat = sigma_i + gamma_i*sigma_i. TODO Args: """ if self.config.s_min <= sigma <= self.config.s_max: gamma = min(self.config.s_churn / state.num_inference_steps, 2**0.5 - 1) else: gamma = 0 # sample eps ~ N(0, S_noise^2 * I) key = random.split(key, num=1) eps = self.config.s_noise * random.normal(key=key, shape=sample.shape) sigma_hat = sigma + gamma * sigma sample_hat = sample + ((sigma_hat**2 - sigma**2) ** 0.5 * eps) return sample_hat, sigma_hat def step( self, state: KarrasVeSchedulerState, model_output: jnp.ndarray, sigma_hat: float, sigma_prev: float, sample_hat: jnp.ndarray, return_dict: bool = True, ) -> Union[FlaxKarrasVeOutput, 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: state (`KarrasVeSchedulerState`): the `FlaxKarrasVeScheduler` state data class. model_output (`torch.FloatTensor` or `np.ndarray`): direct output from learned diffusion model. sigma_hat (`float`): TODO sigma_prev (`float`): TODO sample_hat (`torch.FloatTensor` or `np.ndarray`): TODO return_dict (`bool`): option for returning tuple rather than FlaxKarrasVeOutput class Returns: [`~schedulers.scheduling_karras_ve_flax.FlaxKarrasVeOutput`] or `tuple`: Updated sample in the diffusion chain and derivative. [`~schedulers.scheduling_karras_ve_flax.FlaxKarrasVeOutput`] if `return_dict` is True, otherwise a `tuple`. When returning a tuple, the first element is the sample tensor. """ pred_original_sample = sample_hat + sigma_hat * model_output derivative = (sample_hat - pred_original_sample) / sigma_hat sample_prev = sample_hat + (sigma_prev - sigma_hat) * derivative if not return_dict: return (sample_prev, derivative, state) return FlaxKarrasVeOutput(prev_sample=sample_prev, derivative=derivative, state=state) def step_correct( self, state: KarrasVeSchedulerState, model_output: jnp.ndarray, sigma_hat: float, sigma_prev: float, sample_hat: jnp.ndarray, sample_prev: jnp.ndarray, derivative: jnp.ndarray, return_dict: bool = True, ) -> Union[FlaxKarrasVeOutput, Tuple]: """ Correct the predicted sample based on the output model_output of the network. TODO complete description Args: state (`KarrasVeSchedulerState`): the `FlaxKarrasVeScheduler` state data class. model_output (`torch.FloatTensor` or `np.ndarray`): direct output from learned diffusion model. sigma_hat (`float`): TODO sigma_prev (`float`): TODO sample_hat (`torch.FloatTensor` or `np.ndarray`): TODO sample_prev (`torch.FloatTensor` or `np.ndarray`): TODO derivative (`torch.FloatTensor` or `np.ndarray`): TODO return_dict (`bool`): option for returning tuple rather than FlaxKarrasVeOutput class Returns: prev_sample (TODO): updated sample in the diffusion chain. derivative (TODO): TODO """ pred_original_sample = sample_prev + sigma_prev * model_output derivative_corr = (sample_prev - pred_original_sample) / sigma_prev sample_prev = sample_hat + (sigma_prev - sigma_hat) * (0.5 * derivative + 0.5 * derivative_corr) if not return_dict: return (sample_prev, derivative, state) return FlaxKarrasVeOutput(prev_sample=sample_prev, derivative=derivative, state=state) def add_noise(self, original_samples, noise, timesteps): raise NotImplementedError()