add karras sampling to the Scheduler abstract class, default is quadratic

src/refiners/foundationals/latent_diffusion/schedulers/ddim.py

@@ -1,5 +1,5 @@
 from torch import Tensor, device as Device, dtype as Dtype, arange, sqrt, float32, tensor
-from refiners.foundationals.latent_diffusion.schedulers.scheduler import Scheduler
+from refiners.foundationals.latent_diffusion.schedulers.scheduler import NoiseSchedule, Scheduler
 
 
 class DDIM(Scheduler):
@@ -9,6 +9,7 @@ class DDIM(Scheduler):
         num_train_timesteps: int = 1_000,
         initial_diffusion_rate: float = 8.5e-4,
         final_diffusion_rate: float = 1.2e-2,
+        noise_schedule: NoiseSchedule = NoiseSchedule.QUADRATIC,
         device: Device | str = "cpu",
         dtype: Dtype = float32,
     ) -> None:
@@ -17,6 +18,7 @@ class DDIM(Scheduler):
             num_train_timesteps,
             initial_diffusion_rate,
             final_diffusion_rate,
+            noise_schedule=noise_schedule,
             device=device,
             dtype=dtype,
         )

src/refiners/foundationals/latent_diffusion/schedulers/dpm_solver.py

@@ -1,4 +1,4 @@
-from refiners.foundationals.latent_diffusion.schedulers.scheduler import Scheduler
+from refiners.foundationals.latent_diffusion.schedulers.scheduler import NoiseSchedule, Scheduler
 import numpy as np
 from torch import Tensor, device as Device, tensor, exp, float32, dtype as Dtype
 from collections import deque
@@ -16,6 +16,7 @@ class DPMSolver(Scheduler):
         num_train_timesteps: int = 1_000,
         initial_diffusion_rate: float = 8.5e-4,
         final_diffusion_rate: float = 1.2e-2,
+        noise_schedule: NoiseSchedule = NoiseSchedule.QUADRATIC,
         device: Device | str = "cpu",
         dtype: Dtype = float32,
     ):
@@ -24,6 +25,7 @@ class DPMSolver(Scheduler):
             num_train_timesteps=num_train_timesteps,
             initial_diffusion_rate=initial_diffusion_rate,
             final_diffusion_rate=final_diffusion_rate,
+            noise_schedule=noise_schedule,
             device=device,
             dtype=dtype,
         )

src/refiners/foundationals/latent_diffusion/schedulers/scheduler.py

@@ -1,10 +1,17 @@
 from abc import ABC, abstractmethod
+from enum import Enum
 from torch import Tensor, device as Device, dtype as DType, linspace, float32, sqrt, log
 from typing import TypeVar
 
 T = TypeVar("T", bound="Scheduler")
 
 
+class NoiseSchedule(str, Enum):
+    UNIFORM = "uniform"
+    QUADRATIC = "quadratic"
+    KARRAS = "karras"
+
+
 class Scheduler(ABC):
     """
     A base class for creating a diffusion model scheduler.
@@ -24,6 +31,7 @@ class Scheduler(ABC):
         num_train_timesteps: int = 1_000,
         initial_diffusion_rate: float = 8.5e-4,
         final_diffusion_rate: float = 1.2e-2,
+        noise_schedule: NoiseSchedule = NoiseSchedule.QUADRATIC,
         device: Device | str = "cpu",
         dtype: DType = float32,
     ):
@@ -33,17 +41,8 @@ class Scheduler(ABC):
         self.num_train_timesteps = num_train_timesteps
         self.initial_diffusion_rate = initial_diffusion_rate
         self.final_diffusion_rate = final_diffusion_rate
-        self.scale_factors = (
-            1.0
-            - linspace(
-                start=initial_diffusion_rate**0.5,
-                end=final_diffusion_rate**0.5,
-                steps=num_train_timesteps,
-                device=device,
-                dtype=dtype,
-            )
-            ** 2
-        )
+        self.noise_schedule = noise_schedule
+        self.scale_factors = self.sample_noise_schedule()
         self.cumulative_scale_factors = sqrt(self.scale_factors.cumprod(dim=0))
         self.noise_std = sqrt(1.0 - self.scale_factors.cumprod(dim=0))
         self.signal_to_noise_ratios = log(self.cumulative_scale_factors) - log(self.noise_std)
@@ -71,6 +70,29 @@ class Scheduler(ABC):
     def steps(self) -> list[int]:
         return list(range(self.num_inference_steps))
 
+    def sample_power_distribution(self, power: float = 2, /) -> Tensor:
+        return (
+            linspace(
+                start=self.initial_diffusion_rate ** (1 / power),
+                end=self.final_diffusion_rate ** (1 / power),
+                steps=self.num_train_timesteps,
+                device=self.device,
+                dtype=self.dtype,
+            )
+            ** power
+        )
+
+    def sample_noise_schedule(self) -> Tensor:
+        match self.noise_schedule:
+            case "uniform":
+                return 1 - self.sample_power_distribution(1)
+            case "quadratic":
+                return 1 - self.sample_power_distribution(2)
+            case "karras":
+                return 1 - self.sample_power_distribution(7)
+            case _:
+                raise ValueError(f"Unknown noise schedule: {self.noise_schedule}")
+
     def add_noise(
         self,
         x: Tensor,