Merge branch 'main' into v_prediction

Co-authored-by: Pedro Cuenca <pedro@huggingface.co>

examples/unconditional_image_generation/train_unconditional.py

@@ -194,16 +194,28 @@ def parse_args():
     )
 
     parser.add_argument(
-        "--predict_epsilon",
-        action="store_true",
-        default=True,
-        help="Whether the model should predict the 'epsilon'/noise error or directly the reconstructed image 'x0'.",
+        "--prediction_type",
+        type=str,
+        default="epsilon",
+        help=(
+            "Whether the model should predict the 'epsilon'/noise error, directly the reconstructed image 'x0', or the"
+            " velocity of the ODE 'velocity'."
+        ),
     )
 
     parser.add_argument("--ddpm_num_steps", type=int, default=1000)
     parser.add_argument("--ddpm_beta_schedule", type=str, default="linear")
 
     args = parser.parse_args()
+
+    message = (
+        "Please make sure to instantiate your training with `--prediction_type=epsilon` instead. E.g. `scheduler ="
+        " DDPMScheduler.from_config(<model_id>, prediction_type=epsilon)`."
+    )
+    predict_epsilon = deprecate("predict_epsilon", "0.10.0", message, take_from=args)
+    if predict_epsilon:
+        args.prediction_type = "epsilon"
+
     env_local_rank = int(os.environ.get("LOCAL_RANK", -1))
     if env_local_rank != -1 and env_local_rank != args.local_rank:
         args.local_rank = env_local_rank
@@ -256,13 +268,13 @@ def main(args):
             "UpBlock2D",
         ),
     )
-    accepts_predict_epsilon = "predict_epsilon" in set(inspect.signature(DDPMScheduler.__init__).parameters.keys())
+    accepts_prediction_type = "prediction_type" in set(inspect.signature(DDPMScheduler.__init__).parameters.keys())
 
-    if accepts_predict_epsilon:
+    if accepts_prediction_type:
         noise_scheduler = DDPMScheduler(
             num_train_timesteps=args.ddpm_num_steps,
             beta_schedule=args.ddpm_beta_schedule,
-            predict_epsilon=args.predict_epsilon,
+            prediction_type=args.prediction_type,
         )
     else:
         noise_scheduler = DDPMScheduler(num_train_timesteps=args.ddpm_num_steps, beta_schedule=args.ddpm_beta_schedule)
@@ -365,7 +377,7 @@ def main(args):
                 # Predict the noise residual
                 model_output = model(noisy_images, timesteps).sample
 
-                if args.predict_epsilon:
+                if args.prediction_type == "epsilon":
                     loss = F.mse_loss(model_output, noise)  # this could have different weights!
                 else:
                     alpha_t = _extract_into_tensor(

examples/v_prediction/train_butterflies.py

@@ -0,0 +1,227 @@
+import glob
+import os
+from dataclasses import dataclass
+
+import torch
+import torch.nn.functional as F
+
+from accelerate import Accelerator
+from datasets import load_dataset
+from diffusers import DDIMPipeline, DDIMScheduler, DDPMPipeline, DDPMScheduler, UNet2DModel
+from diffusers.hub_utils import init_git_repo, push_to_hub
+from diffusers.optimization import get_cosine_schedule_with_warmup
+from PIL import Image
+from torchvision import transforms
+from tqdm.auto import tqdm
+
+
+@dataclass
+class TrainingConfig:
+    image_size = 128  # the generated image resolution
+    train_batch_size = 16
+    eval_batch_size = 16  # how many images to sample during evaluation
+    num_epochs = 50
+    gradient_accumulation_steps = 1
+    learning_rate = 5e-5
+    lr_warmup_steps = 500
+    save_image_epochs = 10
+    save_model_epochs = 30
+    mixed_precision = "fp16"  # `no` for float32, `fp16` for automatic mixed precision
+    output_dir = "ddim-butterflies-128-v-diffusion"  # the model namy locally and on the HF Hub
+
+    push_to_hub = False  # whether to upload the saved model to the HF Hub
+    hub_private_repo = False
+    overwrite_output_dir = True  # overwrite the old model when re-running the notebook
+    seed = 0
+
+
+config = TrainingConfig()
+
+
+config.dataset_name = "huggan/smithsonian_butterflies_subset"
+dataset = load_dataset(config.dataset_name, split="train")
+
+
+preprocess = transforms.Compose(
+    [
+        transforms.Resize((config.image_size, config.image_size)),
+        transforms.RandomHorizontalFlip(),
+        transforms.ToTensor(),
+        transforms.Normalize([0.5], [0.5]),
+    ]
+)
+
+
+def transform(examples):
+    images = [preprocess(image.convert("RGB")) for image in examples["image"]]
+    return {"images": images}
+
+
+dataset.set_transform(transform)
+
+
+train_dataloader = torch.utils.data.DataLoader(dataset, batch_size=config.train_batch_size, shuffle=True)
+
+
+model = UNet2DModel(
+    sample_size=config.image_size,  # the target image resolution
+    in_channels=3,  # the number of input channels, 3 for RGB images
+    out_channels=3,  # the number of output channels
+    layers_per_block=2,  # how many ResNet layers to use per UNet block
+    block_out_channels=(128, 128, 256, 256, 512, 512),  # the number of output channes for each UNet block
+    down_block_types=(
+        "DownBlock2D",  # a regular ResNet downsampling block
+        "DownBlock2D",
+        "DownBlock2D",
+        "DownBlock2D",
+        "AttnDownBlock2D",  # a ResNet downsampling block with spatial self-attention
+        "DownBlock2D",
+    ),
+    up_block_types=(
+        "UpBlock2D",  # a regular ResNet upsampling block
+        "AttnUpBlock2D",  # a ResNet upsampling block with spatial self-attention
+        "UpBlock2D",
+        "UpBlock2D",
+        "UpBlock2D",
+        "UpBlock2D",
+    ),
+)
+
+
+if config.output_dir.startswith("ddpm"):
+    noise_scheduler = DDPMScheduler(
+        num_train_timesteps=1000,
+        beta_schedule="squaredcos_cap_v2",
+        variance_type="v_diffusion",
+        prediction_type="velocity",
+    )
+else:
+    noise_scheduler = DDIMScheduler(
+        num_train_timesteps=1000,
+        beta_schedule="squaredcos_cap_v2",
+        variance_type="v_diffusion",
+        prediction_type="velocity",
+    )
+
+
+optimizer = torch.optim.AdamW(model.parameters(), lr=config.learning_rate)
+
+
+lr_scheduler = get_cosine_schedule_with_warmup(
+    optimizer=optimizer,
+    num_warmup_steps=config.lr_warmup_steps,
+    num_training_steps=(len(train_dataloader) * config.num_epochs),
+)
+
+
+def make_grid(images, rows, cols):
+    w, h = images[0].size
+    grid = Image.new("RGB", size=(cols * w, rows * h))
+    for i, image in enumerate(images):
+        grid.paste(image, box=(i % cols * w, i // cols * h))
+    return grid
+
+
+def evaluate(config, epoch, pipeline):
+    # Sample some images from random noise (this is the backward diffusion process).
+    # The default pipeline output type is `List[PIL.Image]`
+    images = pipeline(
+        batch_size=config.eval_batch_size,
+        generator=torch.manual_seed(config.seed),
+    ).images
+
+    # Make a grid out of the images
+    image_grid = make_grid(images, rows=4, cols=4)
+
+    # Save the images
+    test_dir = os.path.join(config.output_dir, "samples")
+    os.makedirs(test_dir, exist_ok=True)
+    image_grid.save(f"{test_dir}/{epoch:04d}.png")
+
+
+def train_loop(config, model, noise_scheduler, optimizer, train_dataloader, lr_scheduler):
+    # Initialize accelerator and tensorboard logging
+    accelerator = Accelerator(
+        mixed_precision=config.mixed_precision,
+        gradient_accumulation_steps=config.gradient_accumulation_steps,
+        log_with="tensorboard",
+        logging_dir=os.path.join(config.output_dir, "logs"),
+    )
+    if accelerator.is_main_process:
+        if config.push_to_hub:
+            repo = init_git_repo(config, at_init=True)
+        accelerator.init_trackers("train_example")
+
+    # Prepare everything
+    # There is no specific order to remember, you just need to unpack the
+    # objects in the same order you gave them to the prepare method.
+    model, optimizer, train_dataloader, lr_scheduler = accelerator.prepare(
+        model, optimizer, train_dataloader, lr_scheduler
+    )
+
+    global_step = 0
+
+    if config.output_dir.startswith("ddpm"):
+        pipeline = DDPMPipeline(unet=accelerator.unwrap_model(model), scheduler=noise_scheduler)
+    else:
+        pipeline = DDIMPipeline(unet=accelerator.unwrap_model(model), scheduler=noise_scheduler)
+
+    evaluate(config, 0, pipeline)
+
+    # Now you train the model
+    for epoch in range(config.num_epochs):
+        progress_bar = tqdm(total=len(train_dataloader), disable=not accelerator.is_local_main_process)
+        progress_bar.set_description(f"Epoch {epoch}")
+
+        for step, batch in enumerate(train_dataloader):
+            clean_images = batch["images"]
+            # Sample noise to add to the images
+            noise = torch.randn(clean_images.shape).to(clean_images.device)
+            bs = clean_images.shape[0]
+
+            # Sample a random timestep for each image
+            timesteps = torch.randint(0, noise_scheduler.num_train_timesteps, (bs,), device=clean_images.device).long()
+
+            with accelerator.accumulate(model):
+                # Predict the noise residual
+                alpha_t, sigma_t = noise_scheduler.get_alpha_sigma(clean_images, timesteps, accelerator.device)
+                z_t = alpha_t * clean_images + sigma_t * noise
+                noise_pred = model(z_t, timesteps).sample
+                v = alpha_t * noise - sigma_t * clean_images
+                loss = F.mse_loss(noise_pred, v)
+                accelerator.backward(loss)
+
+                accelerator.clip_grad_norm_(model.parameters(), 1.0)
+                optimizer.step()
+                lr_scheduler.step()
+                optimizer.zero_grad()
+
+            progress_bar.update(1)
+            logs = {"loss": loss.detach().item(), "lr": lr_scheduler.get_last_lr()[0], "step": global_step}
+            progress_bar.set_postfix(**logs)
+            accelerator.log(logs, step=global_step)
+            global_step += 1
+
+        # After each epoch you optionally sample some demo images with evaluate() and save the model
+        if accelerator.is_main_process:
+            if config.output_dir.startswith("ddpm"):
+                pipeline = DDPMPipeline(unet=accelerator.unwrap_model(model), scheduler=noise_scheduler)
+            else:
+                pipeline = DDIMPipeline(unet=accelerator.unwrap_model(model), scheduler=noise_scheduler)
+
+            if (epoch + 1) % config.save_image_epochs == 0 or epoch == config.num_epochs - 1:
+                evaluate(config, epoch, pipeline)
+
+            if (epoch + 1) % config.save_model_epochs == 0 or epoch == config.num_epochs - 1:
+                if config.push_to_hub:
+                    push_to_hub(config, pipeline, repo, commit_message=f"Epoch {epoch}", blocking=True)
+                else:
+                    pipeline.save_pretrained(config.output_dir)
+
+
+args = (config, model, noise_scheduler, optimizer, train_dataloader, lr_scheduler)
+
+train_loop(*args)
+
+sample_images = sorted(glob.glob(f"{config.output_dir}/samples/*.png"))
+Image.open(sample_images[-1])

src/diffusers/schedulers/scheduling_ddim.py

@@ -24,7 +24,7 @@ import torch
 
 from ..configuration_utils import ConfigMixin, register_to_config
 from ..utils import _COMPATIBLE_STABLE_DIFFUSION_SCHEDULERS, BaseOutput
-from .scheduling_utils import SchedulerMixin
+from .scheduling_utils import SchedulerMixin, expand_to_shape
 
 
 @dataclass
@@ -75,6 +75,18 @@ def betas_for_alpha_bar(num_diffusion_timesteps, max_beta=0.999) -> torch.Tensor
     return torch.tensor(betas)
 
 
+def t_to_alpha_sigma(num_diffusion_timesteps):
+    """Returns the scaling factors for the clean image and for the noise, given
+    a timestep."""
+    alphas = torch.cos(
+        torch.tensor([(t / num_diffusion_timesteps) * math.pi / 2 for t in range(num_diffusion_timesteps)])
+    )
+    sigmas = torch.sin(
+        torch.tensor([(t / num_diffusion_timesteps) * math.pi / 2 for t in range(num_diffusion_timesteps)])
+    )
+    return alphas, sigmas
+
+
 class DDIMScheduler(SchedulerMixin, ConfigMixin):
     """
     Denoising diffusion implicit models is a scheduler that extends the denoising procedure introduced in denoising
@@ -106,6 +118,10 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
             an offset added to the inference steps. You can use a combination of `offset=1` and
             `set_alpha_to_one=False`, to make the last step use step 0 for the previous alpha product, as done in
             stable diffusion.
+        prediction_type (`str`, default `epsilon`, optional):
+            prediction type of the scheduler function, one of `epsilon` (predicting the noise of the diffusion
+            process), `sample` (directly predicting the noisy sample`) or `velocity` (see section 2.4
+            https://imagen.research.google/video/paper.pdf)
 
     """
 
@@ -121,7 +137,10 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
         trained_betas: Optional[np.ndarray] = None,
         clip_sample: bool = True,
         set_alpha_to_one: bool = True,
+        variance_type: str = "fixed",
         steps_offset: int = 0,
+        prediction_type: str = "epsilon",
+        **kwargs,
     ):
         if trained_betas is not None:
             self.betas = torch.from_numpy(trained_betas)
@@ -138,14 +157,22 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
         else:
             raise NotImplementedError(f"{beta_schedule} does is not implemented for {self.__class__}")
 
+        self.variance_type = variance_type
         self.alphas = 1.0 - self.betas
         self.alphas_cumprod = torch.cumprod(self.alphas, dim=0)
+        if prediction_type == "velocity":
+            self.alphas, self.sigmas = t_to_alpha_sigma(num_train_timesteps)
 
         # At every step in ddim, we are looking into the previous alphas_cumprod
         # For the final step, there is no previous alphas_cumprod because we are already at 0
         # `set_alpha_to_one` decides whether we set this parameter simply to one or
         # whether we use the final alpha of the "non-previous" one.
-        self.final_alpha_cumprod = torch.tensor(1.0) if set_alpha_to_one else self.alphas_cumprod[0]
+        if set_alpha_to_one:
+            self.final_alpha_cumprod = torch.tensor(1.0)
+            self.final_sigma = torch.tensor(0.0)  # TODO rename set_alpha_to_one for something general with sigma=0
+        else:
+            self.final_alpha_cumprod = self.alphas_cumprod[0]
+            self.final_sigma = self.sigmas[0] if prediction_type == "velocity" else None
 
         # standard deviation of the initial noise distribution
         self.init_noise_sigma = 1.0
@@ -153,6 +180,8 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
         # setable values
         self.num_inference_steps = None
         self.timesteps = torch.from_numpy(np.arange(0, num_train_timesteps)[::-1].copy().astype(np.int64))
+        self.variance_type = variance_type
+        self.prediction_type = prediction_type
 
     def scale_model_input(self, sample: torch.FloatTensor, timestep: Optional[int] = None) -> torch.FloatTensor:
         """
@@ -162,20 +191,31 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
         Args:
             sample (`torch.FloatTensor`): input sample
             timestep (`int`, optional): current timestep
-
         Returns:
             `torch.FloatTensor`: scaled input sample
         """
         return sample
 
-    def _get_variance(self, timestep, prev_timestep):
+    def _get_variance(self, timestep, prev_timestep, eta=0):
         alpha_prod_t = self.alphas_cumprod[timestep]
         alpha_prod_t_prev = self.alphas_cumprod[prev_timestep] if prev_timestep >= 0 else self.final_alpha_cumprod
         beta_prod_t = 1 - alpha_prod_t
         beta_prod_t_prev = 1 - alpha_prod_t_prev
 
-        variance = (beta_prod_t_prev / beta_prod_t) * (1 - alpha_prod_t / alpha_prod_t_prev)
-
+        if self.variance_type == "fixed":
+            variance = (beta_prod_t_prev / beta_prod_t) * (1 - alpha_prod_t / alpha_prod_t_prev)
+        elif self.variance_type == "v_diffusion":
+            # If eta > 0, adjust the scaling factor for the predicted noise
+            # downward according to the amount of additional noise to add
+            alpha_prev = self.alphas[prev_timestep] if prev_timestep >= 0 else self.final_alpha_cumprod
+            sigma_prev = self.sigmas[prev_timestep] if prev_timestep >= 0 else self.final_sigma
+            if eta:
+                numerator = eta * (sigma_prev**2 / self.sigmas[timestep] ** 2).clamp(min=1.0e-7).sqrt()
+            else:
+                numerator = 0
+            denominator = (1 - self.alphas[timestep] ** 2 / alpha_prev**2).clamp(min=1.0e-7).sqrt()
+            ddim_sigma = (numerator * denominator).clamp(min=1.0e-7)
+            variance = (sigma_prev**2 - ddim_sigma**2).clamp(min=1.0e-7).sqrt()
         return variance
 
     def set_timesteps(self, num_inference_steps: int, device: Union[str, torch.device] = None):
@@ -240,14 +280,14 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
         # Ideally, read DDIM paper in-detail understanding
 
         # Notation (<variable name> -> <name in paper>
-        # - pred_noise_t -> e_theta(x_t, t)
-        # - pred_original_sample -> f_theta(x_t, t) or x_0
+        # - pred_noise_t -> e_theta(x_t, timestep)
+        # - pred_original_sample -> f_theta(x_t, timestep) or x_0
         # - std_dev_t -> sigma_t
         # - eta -> η
         # - pred_sample_direction -> "direction pointing to x_t"
         # - pred_prev_sample -> "x_t-1"
 
-        # 1. get previous step value (=t-1)
+        # 1. get previous step value (=timestep-1)
         prev_timestep = timestep - self.config.num_train_timesteps // self.num_inference_steps
 
         # 2. compute alphas, betas
@@ -258,7 +298,21 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
 
         # 3. compute predicted original sample from predicted noise also called
         # "predicted x_0" of formula (12) from https://arxiv.org/pdf/2010.02502.pdf
-        pred_original_sample = (sample - beta_prod_t ** (0.5) * model_output) / alpha_prod_t ** (0.5)
+        if self.prediction_type == "epsilon":
+            pred_original_sample = (sample - beta_prod_t ** (0.5) * model_output) / alpha_prod_t ** (0.5)
+            eps = torch.tensor(1)
+        elif self.prediction_type == "sample":
+            pred_original_sample = model_output
+            eps = torch.tensor(1)
+        elif self.prediction_type == "velocity":
+            # v_t = alpha_t * epsilon - sigma_t * x
+            # need to merge the PRs for sigma to be available in DDPM
+            pred_original_sample = sample * self.alphas[timestep] - model_output * self.sigmas[timestep]
+            eps = model_output * self.alphas[timestep] + sample * self.sigmas[timestep]
+        else:
+            raise ValueError(
+                f"prediction_type given as {self.prediction_type} must be one of `epsilon`, `sample`, or `velocity`"
+            )
 
         # 4. Clip "predicted x_0"
         if self.config.clip_sample:
@@ -266,7 +320,7 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
 
         # 5. compute variance: "sigma_t(η)" -> see formula (16)
         # σ_t = sqrt((1 − α_t−1)/(1 − α_t)) * sqrt(1 − α_t/α_t−1)
-        variance = self._get_variance(timestep, prev_timestep)
+        variance = self._get_variance(timestep, prev_timestep, eta)
         std_dev_t = eta * variance ** (0.5)
 
         if use_clipped_model_output:
@@ -274,10 +328,14 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
             model_output = (sample - alpha_prod_t ** (0.5) * pred_original_sample) / beta_prod_t ** (0.5)
 
         # 6. compute "direction pointing to x_t" of formula (12) from https://arxiv.org/pdf/2010.02502.pdf
-        pred_sample_direction = (1 - alpha_prod_t_prev - std_dev_t**2) ** (0.5) * model_output
+        if self.prediction_type == "epsilon":
+            pred_sample_direction = (1 - alpha_prod_t_prev - std_dev_t**2) ** (0.5) * model_output
 
-        # 7. compute x_t without "random noise" of formula (12) from https://arxiv.org/pdf/2010.02502.pdf
-        prev_sample = alpha_prod_t_prev ** (0.5) * pred_original_sample + pred_sample_direction
+            # 7. compute x_t without "random noise" of formula (12) from https://arxiv.org/pdf/2010.02502.pdf
+            prev_sample = alpha_prod_t_prev ** (0.5) * pred_original_sample + eps * pred_sample_direction
+        else:
+            alpha_prev = self.alphas[prev_timestep] if prev_timestep >= 0 else self.final_alpha_cumprod
+            prev_sample = pred_original_sample * alpha_prev + eps * variance
 
         if eta > 0:
             # randn_like does not support generator https://github.com/pytorch/pytorch/issues/27072
@@ -300,7 +358,6 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
             variance = self._get_variance(timestep, prev_timestep) ** (0.5) * eta * variance_noise
 
             prev_sample = prev_sample + variance
-
         if not return_dict:
             return (prev_sample,)
 
@@ -312,6 +369,10 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
         noise: torch.FloatTensor,
         timesteps: torch.IntTensor,
     ) -> torch.FloatTensor:
+        if self.variance_type == "v_diffusion":
+            alpha, sigma = self.get_alpha_sigma(original_samples, timesteps, original_samples.device)
+            z_t = alpha * original_samples + sigma * noise
+            return z_t
         # Make sure alphas_cumprod and timestep have same device and dtype as original_samples
         self.alphas_cumprod = self.alphas_cumprod.to(device=original_samples.device, dtype=original_samples.dtype)
         timesteps = timesteps.to(original_samples.device)
@@ -331,3 +392,8 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
 
     def __len__(self):
         return self.config.num_train_timesteps
+
+    def get_alpha_sigma(self, sample, timesteps, device):
+        alpha = expand_to_shape(self.alphas, timesteps, sample.shape, device)
+        sigma = expand_to_shape(self.sigmas, timesteps, sample.shape, device)
+        return alpha, sigma

src/diffusers/schedulers/scheduling_ddpm.py

@@ -23,7 +23,7 @@ import torch
 
 from ..configuration_utils import ConfigMixin, FrozenDict, register_to_config
 from ..utils import _COMPATIBLE_STABLE_DIFFUSION_SCHEDULERS, BaseOutput, deprecate
-from .scheduling_utils import SchedulerMixin
+from .scheduling_utils import SchedulerMixin, expand_to_shape
 
 
 @dataclass
@@ -99,9 +99,12 @@ class DDPMScheduler(SchedulerMixin, ConfigMixin):
             `fixed_small_log`, `fixed_large`, `fixed_large_log`, `learned` or `learned_range`.
         clip_sample (`bool`, default `True`):
             option to clip predicted sample between -1 and 1 for numerical stability.
-        predict_epsilon (`bool`):
-            optional flag to use when the model predicts the noise (epsilon), or the samples instead of the noise.
-
+        prediction_type (`str`, default `epsilon`, optional):
+                prediction type of the scheduler function, one of `epsilon` (predicting the noise of the diffusion
+                process), `sample` (directly predicting the noisy sample`) or `velocity` (see section 2.4
+                https://imagen.research.google/video/paper.pdf)
+        predict_epsilon (`bool`, default `True`):
+            deprecated flag (removing v0.10.0) for epsilon vs. direct sample prediction.
     """
 
     _compatibles = _COMPATIBLE_STABLE_DIFFUSION_SCHEDULERS.copy()
@@ -116,6 +119,7 @@ class DDPMScheduler(SchedulerMixin, ConfigMixin):
         trained_betas: Optional[np.ndarray] = None,
         variance_type: str = "fixed_small",
         clip_sample: bool = True,
+        prediction_type: str = "epsilon",
         predict_epsilon: bool = True,
     ):
         if trained_betas is not None:
@@ -139,7 +143,8 @@ class DDPMScheduler(SchedulerMixin, ConfigMixin):
 
         self.alphas = 1.0 - self.betas
         self.alphas_cumprod = torch.cumprod(self.alphas, dim=0)
-        self.one = torch.tensor(1.0)
+        self.sqrt_alphas_cumprod = torch.sqrt(self.alphas_cumprod)
+        self.sqrt_one_minus_alphas_cumprod = torch.sqrt(1 - self.alphas_cumprod)
 
         # standard deviation of the initial noise distribution
         self.init_noise_sigma = 1.0
@@ -149,6 +154,13 @@ class DDPMScheduler(SchedulerMixin, ConfigMixin):
         self.timesteps = torch.from_numpy(np.arange(0, num_train_timesteps)[::-1].copy())
 
         self.variance_type = variance_type
+        self.prediction_type = prediction_type
+
+        message = (
+            "Please make sure to instantiate your scheduler with `prediction_type=epsilon` instead. E.g. `scheduler ="
+            " DDPMScheduler.from_config(<model_id>, prediction_type='epsilon')`."
+        )
+        deprecate("predict_epsilon", "0.10.0", message)
 
     def scale_model_input(self, sample: torch.FloatTensor, timestep: Optional[int] = None) -> torch.FloatTensor:
         """
@@ -179,14 +191,14 @@ class DDPMScheduler(SchedulerMixin, ConfigMixin):
         )[::-1].copy()
         self.timesteps = torch.from_numpy(timesteps).to(device)
 
-    def _get_variance(self, t, predicted_variance=None, variance_type=None):
-        alpha_prod_t = self.alphas_cumprod[t]
-        alpha_prod_t_prev = self.alphas_cumprod[t - 1] if t > 0 else self.one
+    def _get_variance(self, timestep, predicted_variance=None, variance_type=None):
+        alpha_prod_t = self.alphas_cumprod[timestep]
+        alpha_prod_t_prev = self.alphas_cumprod[timestep - 1] if timestep > 0 else torch.tensor(1.0)
 
-        # For t > 0, compute predicted variance βt (see formula (6) and (7) from https://arxiv.org/pdf/2006.11239.pdf)
+        # For timestep > 0, compute predicted variance βt (see formula (6) and (7) from https://arxiv.org/pdf/2006.11239.pdf)
         # and sample from it to get previous sample
-        # x_{t-1} ~ N(pred_prev_sample, variance) == add variance to pred_sample
-        variance = (1 - alpha_prod_t_prev) / (1 - alpha_prod_t) * self.betas[t]
+        # x_{timestep-1} ~ N(pred_prev_sample, variance) == add variance to pred_sample
+        variance = (1 - alpha_prod_t_prev) / (1 - alpha_prod_t) * self.betas[timestep]
 
         if variance_type is None:
             variance_type = self.config.variance_type
@@ -199,17 +211,19 @@ class DDPMScheduler(SchedulerMixin, ConfigMixin):
             variance = torch.log(torch.clamp(variance, min=1e-20))
             variance = torch.exp(0.5 * variance)
         elif variance_type == "fixed_large":
-            variance = self.betas[t]
+            variance = self.betas[timestep]
         elif variance_type == "fixed_large_log":
             # Glide max_log
-            variance = torch.log(self.betas[t])
+            variance = torch.log(self.betas[timestep])
         elif variance_type == "learned":
             return predicted_variance
         elif variance_type == "learned_range":
             min_log = variance
-            max_log = self.betas[t]
+            max_log = self.betas[timestep]
             frac = (predicted_variance + 1) / 2
             variance = frac * max_log + (1 - frac) * min_log
+        elif variance_type == "v_diffusion":
+            variance = torch.log(self.betas[timestep] * (1 - alpha_prod_t_prev) / (1 - alpha_prod_t))
 
         return variance
 
@@ -240,9 +254,11 @@ class DDPMScheduler(SchedulerMixin, ConfigMixin):
             returning a tuple, the first element is the sample tensor.
 
         """
+        if self.variance_type == "v_diffusion":
+            assert self.prediction_type == "velocity", "Need to use v prediction with v_diffusion"
         message = (
-            "Please make sure to instantiate your scheduler with `predict_epsilon` instead. E.g. `scheduler ="
-            " DDPMScheduler.from_pretrained(<model_id>, predict_epsilon=True)`."
+            "Please make sure to instantiate your scheduler with `prediction_type=epsilon` instead. E.g. `scheduler ="
+            " DDPMScheduler.from_config(<model_id>, prediction_type=epsilon)`."
         )
         predict_epsilon = deprecate("predict_epsilon", "0.10.0", message, take_from=kwargs)
         if predict_epsilon is not None and predict_epsilon != self.config.predict_epsilon:
@@ -250,34 +266,46 @@ class DDPMScheduler(SchedulerMixin, ConfigMixin):
             new_config["predict_epsilon"] = predict_epsilon
             self._internal_dict = FrozenDict(new_config)
 
-        t = timestep
-
         if model_output.shape[1] == sample.shape[1] * 2 and self.variance_type in ["learned", "learned_range"]:
             model_output, predicted_variance = torch.split(model_output, sample.shape[1], dim=1)
         else:
             predicted_variance = None
 
         # 1. compute alphas, betas
-        alpha_prod_t = self.alphas_cumprod[t]
-        alpha_prod_t_prev = self.alphas_cumprod[t - 1] if t > 0 else self.one
+        alpha_prod_t = self.alphas_cumprod[timestep]
+        alpha_prod_t_prev = self.alphas_cumprod[timestep - 1] if timestep > 0 else torch.tensor(1.0)
         beta_prod_t = 1 - alpha_prod_t
         beta_prod_t_prev = 1 - alpha_prod_t_prev
 
         # 2. compute predicted original sample from predicted noise also called
         # "predicted x_0" of formula (15) from https://arxiv.org/pdf/2006.11239.pdf
-        if self.config.predict_epsilon:
-            pred_original_sample = (sample - beta_prod_t ** (0.5) * model_output) / alpha_prod_t ** (0.5)
-        else:
+        if self.prediction_type == "velocity":
+            # x_recon in p_mean_variance
+            pred_original_sample = (
+                sample * self.sqrt_alphas_cumprod[timestep]
+                - model_output * self.sqrt_one_minus_alphas_cumprod[timestep]
+            )
+
+        # not check on predict_epsilon for depreciation flag above
+        elif self.prediction_type == "sample" or not self.config.predict_epsilon:
             pred_original_sample = model_output
 
+        elif self.prediction_type == "epsilon" or self.config.predict_epsilon:
+            pred_original_sample = (sample - beta_prod_t ** (0.5) * model_output) / alpha_prod_t ** (0.5)
+
+        else:
+            raise ValueError(
+                f"prediction_type given as {self.prediction_type} must be one of `epsilon`, `sample`, or `velocity`"
+            )
+
         # 3. Clip "predicted x_0"
         if self.config.clip_sample:
             pred_original_sample = torch.clamp(pred_original_sample, -1, 1)
 
         # 4. Compute coefficients for pred_original_sample x_0 and current sample x_t
         # See formula (7) from https://arxiv.org/pdf/2006.11239.pdf
-        pred_original_sample_coeff = (alpha_prod_t_prev ** (0.5) * self.betas[t]) / beta_prod_t
-        current_sample_coeff = self.alphas[t] ** (0.5) * beta_prod_t_prev / beta_prod_t
+        pred_original_sample_coeff = (alpha_prod_t_prev ** (0.5) * self.betas[timestep]) / beta_prod_t
+        current_sample_coeff = self.alphas[timestep] ** (0.5) * beta_prod_t_prev / beta_prod_t
 
         # 5. Compute predicted previous sample µ_t
         # See formula (7) from https://arxiv.org/pdf/2006.11239.pdf
@@ -285,7 +313,7 @@ class DDPMScheduler(SchedulerMixin, ConfigMixin):
 
         # 6. Add noise
         variance = 0
-        if t > 0:
+        if timestep > 0:
             device = model_output.device
             if device.type == "mps":
                 # randn does not work reproducibly on mps
@@ -296,9 +324,13 @@ class DDPMScheduler(SchedulerMixin, ConfigMixin):
                     model_output.shape, generator=generator, device=device, dtype=model_output.dtype
                 )
             if self.variance_type == "fixed_small_log":
-                variance = self._get_variance(t, predicted_variance=predicted_variance) * variance_noise
+                variance = self._get_variance(timestep, predicted_variance=predicted_variance) * variance_noise
+            elif self.variance_type == "v_diffusion":
+                variance = torch.exp(0.5 * self._get_variance(timestep, predicted_variance)) * variance_noise
             else:
-                variance = (self._get_variance(t, predicted_variance=predicted_variance) ** 0.5) * variance_noise
+                variance = (
+                    self._get_variance(timestep, predicted_variance=predicted_variance) ** 0.5
+                ) * variance_noise
 
         pred_prev_sample = pred_prev_sample + variance
 
@@ -313,6 +345,11 @@ class DDPMScheduler(SchedulerMixin, ConfigMixin):
         noise: torch.FloatTensor,
         timesteps: torch.IntTensor,
     ) -> torch.FloatTensor:
+        if self.variance_type == "v_diffusion":
+            alpha, sigma = self.get_alpha_sigma(original_samples, timesteps, original_samples.device)
+            z_t = alpha * original_samples + sigma * noise
+            return z_t
+
         # Make sure alphas_cumprod and timestep have same device and dtype as original_samples
         self.alphas_cumprod = self.alphas_cumprod.to(device=original_samples.device, dtype=original_samples.dtype)
         timesteps = timesteps.to(original_samples.device)
@@ -332,3 +369,8 @@ class DDPMScheduler(SchedulerMixin, ConfigMixin):
 
     def __len__(self):
         return self.config.num_train_timesteps
+
+    def get_alpha_sigma(self, sample, timesteps, device):
+        alpha = expand_to_shape(self.sqrt_alphas_cumprod, timesteps, sample.shape, device)
+        sigma = expand_to_shape(self.sqrt_one_minus_alphas_cumprod, timesteps, sample.shape, device)
+        return alpha, sigma

src/diffusers/schedulers/scheduling_dpmsolver_multistep.py

@@ -21,7 +21,7 @@ import numpy as np
 import torch
 
 from ..configuration_utils import ConfigMixin, register_to_config
-from ..utils import _COMPATIBLE_STABLE_DIFFUSION_SCHEDULERS
+from ..utils import _COMPATIBLE_STABLE_DIFFUSION_SCHEDULERS, deprecate
 from .scheduling_utils import SchedulerMixin, SchedulerOutput
 
 
@@ -88,9 +88,13 @@ class DPMSolverMultistepScheduler(SchedulerMixin, ConfigMixin):
             the order of DPM-Solver; can be `1` or `2` or `3`. We recommend to use `solver_order=2` for guided
             sampling, and `solver_order=3` for unconditional sampling.
         predict_epsilon (`bool`, default `True`):
-            we currently support both the noise prediction model and the data prediction model. If the model predicts
-            the noise / epsilon, set `predict_epsilon` to `True`. If the model predicts the data / x0 directly, set
-            `predict_epsilon` to `False`.
+            deprecated flag (removing v0.10.0); we currently support both the noise prediction model and the data
+            prediction model. If the model predicts the noise / epsilon, set `predict_epsilon` to `True`. If the model
+            predicts the data / x0 directly, set `predict_epsilon` to `False`.
+        prediction_type (`str`, default `epsilon`, optional):
+            prediction type of the scheduler function, one of `epsilon` (predicting the noise of the diffusion
+            process), `sample` (directly predicting the noisy sample`) or `velocity` (see section 2.4
+            https://imagen.research.google/video/paper.pdf)
         thresholding (`bool`, default `False`):
             whether to use the "dynamic thresholding" method (introduced by Imagen, https://arxiv.org/abs/2205.11487).
             For pixel-space diffusion models, you can set both `algorithm_type=dpmsolver++` and `thresholding=True` to
@@ -128,6 +132,7 @@ class DPMSolverMultistepScheduler(SchedulerMixin, ConfigMixin):
         beta_schedule: str = "linear",
         trained_betas: Optional[np.ndarray] = None,
         solver_order: int = 2,
+        prediction_type: str = "epsilon",
         predict_epsilon: bool = True,
         thresholding: bool = False,
         dynamic_thresholding_ratio: float = 0.995,
@@ -174,6 +179,17 @@ class DPMSolverMultistepScheduler(SchedulerMixin, ConfigMixin):
         self.model_outputs = [None] * solver_order
         self.lower_order_nums = 0
 
+        if prediction_type not in ["epsilon", "sample"]:
+            raise ValueError(
+                f"Prediction type {self.config.prediction_type} not supported by DPMSolverMultistepScheduler"
+            )
+
+        message = (
+            "Please make sure to instantiate your scheduler with `prediction_type=epsilon` instead. E.g. `scheduler ="
+            " DDPMScheduler.from_config(<model_id>, prediction_type='epsilon')`."
+        )
+        deprecate("predict_epsilon", "0.10.0", message)
+
     def set_timesteps(self, num_inference_steps: int, device: Union[str, torch.device] = None):
         """
         Sets the timesteps used for the diffusion chain. Supporting function to be run before inference.
@@ -221,11 +237,15 @@ class DPMSolverMultistepScheduler(SchedulerMixin, ConfigMixin):
         """
         # DPM-Solver++ needs to solve an integral of the data prediction model.
         if self.config.algorithm_type == "dpmsolver++":
-            if self.config.predict_epsilon:
+            if self.config.prediction_type == "epsilon":
                 alpha_t, sigma_t = self.alpha_t[timestep], self.sigma_t[timestep]
                 x0_pred = (sample - sigma_t * model_output) / alpha_t
-            else:
+            elif self.config.prediction_type == "sample":
                 x0_pred = model_output
+            else:
+                raise ValueError(
+                    f"Prediction type {self.config.prediction_type} not supported by DPMSolverMultistepScheduler"
+                )
             if self.config.thresholding:
                 # Dynamic thresholding in https://arxiv.org/abs/2205.11487
                 dynamic_max_val = torch.quantile(

src/diffusers/schedulers/scheduling_utils.py

@@ -152,3 +152,14 @@ class SchedulerMixin:
             getattr(diffusers_library, c) for c in compatible_classes_str if hasattr(diffusers_library, c)
         ]
         return compatible_classes
+
+
+def expand_to_shape(input, timesteps, shape, device):
+    """
+    Helper indexes a 1D tensor `input` using a 1D index tensor `timesteps`, then reshapes the result to broadcast
+    nicely with `shape`. Useful for parallelizing operations over `shape[0]` number of diffusion steps at once.
+    """
+    out = torch.gather(input.to(device), 0, timesteps.to(device))
+    reshape = [shape[0]] + [1] * (len(shape) - 1)
+    out = out.reshape(*reshape)
+    return out

tests/test_scheduler.py

@@ -599,9 +599,9 @@ class DDPMSchedulerTest(SchedulerCommonTest):
         for clip_sample in [True, False]:
             self.check_over_configs(clip_sample=clip_sample)
 
-    def test_predict_epsilon(self):
-        for predict_epsilon in [True, False]:
-            self.check_over_configs(predict_epsilon=predict_epsilon)
+    def test_prediction_type(self):
+        for prediction_type in ["epsilon", "sample", "velocity"]:
+            self.check_over_configs(prediction_type=prediction_type)
 
     def test_deprecated_epsilon(self):
         deprecate("remove this test", "0.10.0", "remove")
@@ -613,7 +613,7 @@ class DDPMSchedulerTest(SchedulerCommonTest):
         time_step = 4
 
         scheduler = scheduler_class(**scheduler_config)
-        scheduler_eps = scheduler_class(predict_epsilon=False, **scheduler_config)
+        scheduler_eps = scheduler_class(prediction_type="sample", **scheduler_config)
 
         kwargs = {}
         if "generator" in set(inspect.signature(scheduler.step).parameters.keys()):
@@ -728,6 +728,10 @@ class DDIMSchedulerTest(SchedulerCommonTest):
         for schedule in ["linear", "squaredcos_cap_v2"]:
             self.check_over_configs(beta_schedule=schedule)
 
+    def test_prediction_type(self):
+        for prediction_type in ["epsilon", "sample", "velocity"]:
+            self.check_over_configs(prediction_type=prediction_type)
+
     def test_clip_sample(self):
         for clip_sample in [True, False]:
             self.check_over_configs(clip_sample=clip_sample)