Fast Sampling of Diffusion Models with Exponential Integrator.
Original paper can be found here. The original implementation can be found here.
( num_train_timesteps: int = 1000 beta_start: float = 0.0001 beta_end: float = 0.02 beta_schedule: str = 'linear' trained_betas: typing.Optional[numpy.ndarray] = None solver_order: int = 2 prediction_type: str = 'epsilon' thresholding: bool = False dynamic_thresholding_ratio: float = 0.995 sample_max_value: float = 1.0 algorithm_type: str = 'deis' solver_type: str = 'logrho' lower_order_final: bool = True )
Parameters
int) — number of diffusion steps used to train the model.
float) — the starting beta value of inference.
float) — the final beta value.
str) —
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.
np.ndarray, optional) —
option to pass an array of betas directly to the constructor to bypass beta_start, beta_end etc.
int, default 2) —
the order of DEIS; can be 1 or 2 or 3. We recommend to use solver_order=2 for guided sampling, and
solver_order=3 for unconditional sampling.
str, default epsilon) —
indicates whether the model predicts the noise (epsilon), or the data / x0. One of epsilon, sample,
or v-prediction.
bool, default False) —
whether to use the “dynamic thresholding” method (introduced by Imagen, https://arxiv.org/abs/2205.11487).
Note that the thresholding method is unsuitable for latent-space diffusion models (such as
stable-diffusion).
float, default 0.995) —
the ratio for the dynamic thresholding method. Default is 0.995, the same as Imagen
(https://arxiv.org/abs/2205.11487).
float, default 1.0) —
the threshold value for dynamic thresholding. Valid woks when thresholding=True
str, default deis) —
the algorithm type for the solver. current we support multistep deis, we will add other variants of DEIS in
the future
bool, default True) —
whether to use lower-order solvers in the final steps. Only valid for < 15 inference steps. We empirically
find this trick can stabilize the sampling of DEIS for steps < 15, especially for steps <= 10.
DEIS (https://arxiv.org/abs/2204.13902) is a fast high order solver for diffusion ODEs. We slightly modify the polynomial fitting formula in log-rho space instead of the original linear t space in DEIS paper. The modification enjoys closed-form coefficients for exponential multistep update instead of replying on the numerical solver. More variants of DEIS can be found in https://github.com/qsh-zh/deis.
Currently, we support the log-rho multistep DEIS. We recommend to use solver_order=2 / 3 while solver_order=1
reduces to DDIM.
We also support the “dynamic thresholding” method in Imagen (https://arxiv.org/abs/2205.11487). For pixel-space
diffusion models, you can set thresholding=True to use the dynamic thresholding.
~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
from_pretrained() functions.
(
model_output: FloatTensor
timestep: int
sample: FloatTensor
)
→
torch.FloatTensor
Parameters
torch.FloatTensor) — direct output from learned diffusion model.
int) — current discrete timestep in the diffusion chain.
torch.FloatTensor) —
current instance of sample being created by diffusion process.
Returns
torch.FloatTensor
the converted model output.
Convert the model output to the corresponding type that the algorithm DEIS needs.
(
model_output: FloatTensor
timestep: int
prev_timestep: int
sample: FloatTensor
)
→
torch.FloatTensor
Parameters
torch.FloatTensor) — direct output from learned diffusion model.
int) — current discrete timestep in the diffusion chain.
int) — previous discrete timestep in the diffusion chain.
torch.FloatTensor) —
current instance of sample being created by diffusion process.
Returns
torch.FloatTensor
the sample tensor at the previous timestep.
One step for the first-order DEIS (equivalent to DDIM).
(
model_output_list: typing.List[torch.FloatTensor]
timestep_list: typing.List[int]
prev_timestep: int
sample: FloatTensor
)
→
torch.FloatTensor
Parameters
List[torch.FloatTensor]) —
direct outputs from learned diffusion model at current and latter timesteps.
int) — current and latter discrete timestep in the diffusion chain.
int) — previous discrete timestep in the diffusion chain.
torch.FloatTensor) —
current instance of sample being created by diffusion process.
Returns
torch.FloatTensor
the sample tensor at the previous timestep.
One step for the second-order multistep DEIS.
(
model_output_list: typing.List[torch.FloatTensor]
timestep_list: typing.List[int]
prev_timestep: int
sample: FloatTensor
)
→
torch.FloatTensor
Parameters
List[torch.FloatTensor]) —
direct outputs from learned diffusion model at current and latter timesteps.
int) — current and latter discrete timestep in the diffusion chain.
int) — previous discrete timestep in the diffusion chain.
torch.FloatTensor) —
current instance of sample being created by diffusion process.
Returns
torch.FloatTensor
the sample tensor at the previous timestep.
One step for the third-order multistep DEIS.
(
sample: FloatTensor
*args
**kwargs
)
→
torch.FloatTensor
Ensures interchangeability with schedulers that need to scale the denoising model input depending on the current timestep.
( num_inference_steps: int device: typing.Union[str, torch.device] = None )
Sets the timesteps used for the diffusion chain. Supporting function to be run before inference.
(
model_output: FloatTensor
timestep: int
sample: FloatTensor
return_dict: bool = True
)
→
~scheduling_utils.SchedulerOutput or tuple
Parameters
torch.FloatTensor) — direct output from learned diffusion model.
int) — current discrete timestep in the diffusion chain.
torch.FloatTensor) —
current instance of sample being created by diffusion process.
bool) — option for returning tuple rather than SchedulerOutput class
Returns
~scheduling_utils.SchedulerOutput or tuple
~scheduling_utils.SchedulerOutput if return_dict is
True, otherwise a tuple. When returning a tuple, the first element is the sample tensor.
Step function propagating the sample with the multistep DEIS.