# Copyright 2024 Stability AI, Katherine Crowson and The HuggingFace Team. All rights reserved.
#
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#
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# their software and algorithms, including trained model weights, parameters (including
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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.schedulers.scheduling_utils import SchedulerMixin
from diffusers.utils import BaseOutput, logging
logger = logging.get_logger(__name__) # pylint: disable=invalid-name
@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 FlowMatchEulerDiscreteScheduler(SchedulerMixin, ConfigMixin):
"""
NOTE: this is very similar to diffusers.FlowMatchEulerDiscreteScheduler. Except our timesteps are reversed
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,
use_dynamic_shifting=False,
):
timesteps = np.linspace(1, num_train_timesteps, num_train_timesteps, dtype=np.float32).copy()
timesteps = torch.from_numpy(timesteps).to(dtype=torch.float32)
sigmas = timesteps / num_train_timesteps
if not use_dynamic_shifting:
# when use_dynamic_shifting is True, we apply the timestep shifting on the fly based on the image resolution
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
self.sigma_min = self.sigmas[-1].item()
self.sigma_max = self.sigmas[0].item()
@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 scale_noise(
self,
sample: torch.FloatTensor,
timestep: Union[float, torch.FloatTensor],
noise: Optional[torch.FloatTensor] = None,
) -> torch.FloatTensor:
"""
Forward process in flow-matching
Args:
sample (`torch.FloatTensor`):
The input sample.
timestep (`int`, *optional*):
The current timestep in the diffusion chain.
Returns:
`torch.FloatTensor`:
A scaled input sample.
"""
# Make sure sigmas and timesteps have the same device and dtype as original_samples
sigmas = self.sigmas.to(device=sample.device, dtype=sample.dtype)
if sample.device.type == "mps" and torch.is_floating_point(timestep):
# mps does not support float64
schedule_timesteps = self.timesteps.to(sample.device, dtype=torch.float32)
timestep = timestep.to(sample.device, dtype=torch.float32)
else:
schedule_timesteps = self.timesteps.to(sample.device)
timestep = timestep.to(sample.device)
# self.begin_index is None when scheduler is used for training, or pipeline does not implement set_begin_index
if self.begin_index is None:
step_indices = [self.index_for_timestep(t, schedule_timesteps) for t in timestep]
elif self.step_index is not None:
# add_noise is called after first denoising step (for inpainting)
step_indices = [self.step_index] * timestep.shape[0]
else:
# add noise is called before first denoising step to create initial latent(img2img)
step_indices = [self.begin_index] * timestep.shape[0]
sigma = sigmas[step_indices].flatten()
while len(sigma.shape) < len(sample.shape):
sigma = sigma.unsqueeze(-1)
sample = sigma * noise + (1.0 - sigma) * sample
return sample
def _sigma_to_t(self, sigma):
return sigma * self.config.num_train_timesteps
def time_shift(self, mu: float, sigma: float, t: torch.Tensor):
return math.exp(mu) / (math.exp(mu) + (1 / t - 1) ** sigma)
def set_timesteps(
self,
num_inference_steps: int = None,
device: Union[str, torch.device] = None,
sigmas: Optional[List[float]] = None,
mu: Optional[float] = 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.
device (`str` or `torch.device`, *optional*):
The device to which the timesteps should be moved to. If `None`, the timesteps are not moved.
"""
if self.config.use_dynamic_shifting and mu is None:
raise ValueError(" you have a pass a value for `mu` when `use_dynamic_shifting` is set to be `True`")
if sigmas is None:
self.num_inference_steps = num_inference_steps
timesteps = np.linspace(
self._sigma_to_t(self.sigma_max), self._sigma_to_t(self.sigma_min), num_inference_steps
)
sigmas = timesteps / self.config.num_train_timesteps
if self.config.use_dynamic_shifting:
sigmas = self.time_shift(mu, 1.0, sigmas)
else:
sigmas = self.config.shift * sigmas / (1 + (self.config.shift - 1) * sigmas)
sigmas = torch.from_numpy(sigmas).to(dtype=torch.float32, device=device)
timesteps = sigmas * self.config.num_train_timesteps
self.timesteps = timesteps.to(device=device)
self.sigmas = torch.cat([sigmas, torch.ones(1, device=sigmas.device)])
self._step_index = None
self._begin_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,
s_churn: float = 0.0,
s_tmin: float = 0.0,
s_tmax: float = float("inf"),
s_noise: float = 1.0,
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.
s_churn (`float`):
s_tmin (`float`):
s_tmax (`float`):
s_noise (`float`, defaults to 1.0):
Scaling factor for noise added to the sample.
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._init_step_index(timestep)
# 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
@dataclass
class ConsistencyFlowMatchEulerDiscreteSchedulerOutput(BaseOutput):
prev_sample: torch.FloatTensor
pred_original_sample: torch.FloatTensor
class ConsistencyFlowMatchEulerDiscreteScheduler(SchedulerMixin, ConfigMixin):
_compatibles = []
order = 1
@register_to_config
def __init__(
self,
num_train_timesteps: int = 1000,
pcm_timesteps: int = 50,
):
sigmas = np.linspace(0, 1, num_train_timesteps)
step_ratio = num_train_timesteps // pcm_timesteps
euler_timesteps = (np.arange(1, pcm_timesteps) * step_ratio).round().astype(np.int64) - 1
euler_timesteps = np.asarray([0] + euler_timesteps.tolist())
self.euler_timesteps = euler_timesteps
self.sigmas = sigmas[self.euler_timesteps]
self.sigmas = torch.from_numpy((self.sigmas.copy()))
self.timesteps = self.sigmas * num_train_timesteps
self._step_index = None
self._begin_index = None
self.sigmas = self.sigmas.to("cpu") # to avoid too much CPU/GPU communication
@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 = None,
device: Union[str, torch.device] = None,
sigmas: Optional[List[float]] = 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.
device (`str` or `torch.device`, *optional*):
The device to which the timesteps should be moved to. If `None`, the timesteps are not moved.
"""
self.num_inference_steps = num_inference_steps if num_inference_steps is not None else len(sigmas)
inference_indices = np.linspace(
0, self.config.pcm_timesteps, num=self.num_inference_steps, endpoint=False
)
inference_indices = np.floor(inference_indices).astype(np.int64)
inference_indices = torch.from_numpy(inference_indices).long()
self.sigmas_ = self.sigmas[inference_indices]
timesteps = self.sigmas_ * self.config.num_train_timesteps
self.timesteps = timesteps.to(device=device)
self.sigmas_ = torch.cat(
[self.sigmas_, torch.ones(1, device=self.sigmas_.device)]
)
self._step_index = None
self._begin_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[ConsistencyFlowMatchEulerDiscreteSchedulerOutput, Tuple]:
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._init_step_index(timestep)
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
prev_sample = prev_sample.to(model_output.dtype)
pred_original_sample = sample + (1.0 - sigma) * model_output
pred_original_sample = pred_original_sample.to(model_output.dtype)
self._step_index += 1
if not return_dict:
return (prev_sample,)
return ConsistencyFlowMatchEulerDiscreteSchedulerOutput(prev_sample=prev_sample,
pred_original_sample=pred_original_sample)
def __len__(self):
return self.config.num_train_timesteps