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https://github.com/modelscope/DiffSynth-Studio.git
synced 2026-04-24 06:46:13 +00:00
update sd training scripts
This commit is contained in:
Artiprocher
@@ -1,269 +1,107 @@
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import torch, math
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from typing import Literal
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class DDIMScheduler:
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class DDIMScheduler():
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def __init__(
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self,
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num_train_timesteps: int = 1000,
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beta_start: float = 0.00085,
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beta_end: float = 0.012,
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beta_schedule: Literal["linear", "scaled_linear", "squaredcos_cap_v2"] = "scaled_linear",
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clip_sample: bool = False,
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set_alpha_to_one: bool = False,
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steps_offset: int = 1,
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prediction_type: Literal["epsilon", "sample", "v_prediction"] = "epsilon",
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timestep_spacing: Literal["leading", "trailing", "linspace"] = "leading",
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rescale_betas_zero_snr: bool = False,
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):
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def __init__(self, num_train_timesteps=1000, beta_start=0.00085, beta_end=0.012, beta_schedule="scaled_linear", prediction_type="epsilon", rescale_zero_terminal_snr=False):
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self.num_train_timesteps = num_train_timesteps
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self.beta_start = beta_start
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self.beta_end = beta_end
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self.beta_schedule = beta_schedule
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self.clip_sample = clip_sample
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self.set_alpha_to_one = set_alpha_to_one
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self.steps_offset = steps_offset
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self.prediction_type = prediction_type
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self.timestep_spacing = timestep_spacing
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# Compute betas
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if beta_schedule == "linear":
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self.betas = torch.linspace(beta_start, beta_end, num_train_timesteps, dtype=torch.float32)
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elif beta_schedule == "scaled_linear":
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# SD 1.5 specific: sqrt-linear interpolation
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self.betas = torch.linspace(beta_start ** 0.5, beta_end ** 0.5, num_train_timesteps, dtype=torch.float32) ** 2
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elif beta_schedule == "squaredcos_cap_v2":
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self.betas = self._betas_for_alpha_bar(num_train_timesteps)
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if beta_schedule == "scaled_linear":
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betas = torch.square(torch.linspace(math.sqrt(beta_start), math.sqrt(beta_end), num_train_timesteps, dtype=torch.float32))
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elif beta_schedule == "linear":
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betas = torch.linspace(beta_start, beta_end, num_train_timesteps, dtype=torch.float32)
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else:
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raise ValueError(f"Unsupported beta_schedule: {beta_schedule}")
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# Rescale for zero SNR
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if rescale_betas_zero_snr:
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self.betas = self._rescale_zero_terminal_snr(self.betas)
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self.alphas = 1.0 - self.betas
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self.alphas_cumprod = torch.cumprod(self.alphas, dim=0)
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# For the final step, there is no previous alphas_cumprod
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self.final_alpha_cumprod = torch.tensor(1.0) if set_alpha_to_one else self.alphas_cumprod[0]
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# standard deviation of the initial noise distribution
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self.init_noise_sigma = 1.0
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# Setable values (will be populated by set_timesteps)
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self.num_inference_steps = None
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self.timesteps = torch.from_numpy(self._default_timesteps().astype("int64"))
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raise NotImplementedError(f"{beta_schedule} is not implemented")
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self.alphas_cumprod = torch.cumprod(1.0 - betas, dim=0)
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if rescale_zero_terminal_snr:
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self.alphas_cumprod = self.rescale_zero_terminal_snr(self.alphas_cumprod)
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self.alphas_cumprod = self.alphas_cumprod.tolist()
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self.set_timesteps(10)
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self.prediction_type = prediction_type
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self.training = False
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@staticmethod
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def _betas_for_alpha_bar(num_diffusion_timesteps: int, max_beta: float = 0.999) -> torch.Tensor:
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"""Create beta schedule via cosine alpha_bar function."""
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def alpha_bar_fn(t):
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return math.cos((t + 0.008) / 1.008 * math.pi / 2) ** 2
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betas = []
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for i in range(num_diffusion_timesteps):
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t1 = i / num_diffusion_timesteps
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t2 = (i + 1) / num_diffusion_timesteps
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betas.append(min(1 - alpha_bar_fn(t2) / alpha_bar_fn(t1), max_beta))
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return torch.tensor(betas, dtype=torch.float32)
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@staticmethod
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def _rescale_zero_terminal_snr(betas: torch.Tensor) -> torch.Tensor:
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"""Rescale betas to have zero terminal SNR."""
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alphas = 1.0 - betas
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alphas_cumprod = torch.cumprod(alphas, dim=0)
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def rescale_zero_terminal_snr(self, alphas_cumprod):
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alphas_bar_sqrt = alphas_cumprod.sqrt()
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# Store old values.
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alphas_bar_sqrt_0 = alphas_bar_sqrt[0].clone()
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alphas_bar_sqrt_T = alphas_bar_sqrt[-1].clone()
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# Shift so the last timestep is zero.
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alphas_bar_sqrt -= alphas_bar_sqrt_T
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# Scale so the first timestep is back to the old value.
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alphas_bar_sqrt *= alphas_bar_sqrt_0 / (alphas_bar_sqrt_0 - alphas_bar_sqrt_T)
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alphas_bar = alphas_bar_sqrt ** 2
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alphas = torch.cat([alphas_bar[1:], alphas_bar[:1]])
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return 1 - alphas
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def _default_timesteps(self):
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"""Default timesteps before set_timesteps is called."""
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import numpy as np
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return np.arange(0, self.num_train_timesteps)[::-1].copy().astype(np.int64)
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# Convert alphas_bar_sqrt to betas
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alphas_bar = alphas_bar_sqrt.square() # Revert sqrt
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def _get_variance(self, timestep: int, prev_timestep: int) -> torch.Tensor:
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"""Compute the variance for the DDIM step."""
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alpha_prod_t = self.alphas_cumprod[timestep]
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alpha_prod_t_prev = self.alphas_cumprod[prev_timestep] if prev_timestep >= 0 else self.final_alpha_cumprod
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beta_prod_t = 1 - alpha_prod_t
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beta_prod_t_prev = 1 - alpha_prod_t_prev
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variance = (beta_prod_t_prev / beta_prod_t) * (1 - alpha_prod_t / alpha_prod_t_prev)
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return variance
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return alphas_bar
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def set_timesteps(self, num_inference_steps: int = 100, denoising_strength: float = 1.0, training: bool = False, **kwargs):
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"""
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Sets the discrete timesteps used for the diffusion chain.
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Follows FlowMatchScheduler interface: (num_inference_steps, denoising_strength, training, **kwargs)
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"""
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import numpy as np
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if denoising_strength != 1.0:
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# For img2img: adjust effective steps
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num_inference_steps = int(num_inference_steps * denoising_strength)
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# Compute step ratio
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if self.timestep_spacing == "leading":
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# leading: arange * step_ratio, reverse, then add offset
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step_ratio = self.num_train_timesteps // num_inference_steps
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timesteps = (np.arange(0, num_inference_steps) * step_ratio).round()[::-1].astype(np.int64)
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timesteps = timesteps + self.steps_offset
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elif self.timestep_spacing == "trailing":
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# trailing: timesteps = arange(num_steps, 0, -1) * step_ratio - 1
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step_ratio = self.num_train_timesteps / num_inference_steps
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timesteps = (np.arange(num_inference_steps, 0, -1) * step_ratio - 1).round()[::-1]
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elif self.timestep_spacing == "linspace":
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# linspace: evenly spaced from num_train_timesteps - 1 to 0
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timesteps = np.linspace(0, self.num_train_timesteps - 1, num_inference_steps).round()[::-1]
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def set_timesteps(self, num_inference_steps, denoising_strength=1.0, training=False, **kwargs):
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# The timesteps are aligned to 999...0, which is different from other implementations,
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# but I think this implementation is more reasonable in theory.
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max_timestep = max(round(self.num_train_timesteps * denoising_strength) - 1, 0)
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num_inference_steps = min(num_inference_steps, max_timestep + 1)
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if num_inference_steps == 1:
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self.timesteps = torch.Tensor([max_timestep])
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else:
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raise ValueError(f"Unsupported timestep_spacing: {self.timestep_spacing}")
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step_length = max_timestep / (num_inference_steps - 1)
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self.timesteps = torch.Tensor([round(max_timestep - i*step_length) for i in range(num_inference_steps)])
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self.training = training
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# Clamp timesteps to valid range [0, num_train_timesteps - 1]
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timesteps = np.clip(timesteps, 0, self.num_train_timesteps - 1)
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self.timesteps = torch.from_numpy(timesteps).to(dtype=torch.int64)
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self.num_inference_steps = num_inference_steps
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if training:
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self.set_training_weight()
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self.training = True
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else:
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self.training = False
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def set_training_weight(self):
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"""Set timestep weights for training (similar to FlowMatchScheduler)."""
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steps = 1000
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x = self.timesteps
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y = torch.exp(-2 * ((x - steps / 2) / steps) ** 2)
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y_shifted = y - y.min()
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bsmntw_weighing = y_shifted * (steps / y_shifted.sum())
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if len(self.timesteps) != 1000:
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bsmntw_weighing = bsmntw_weighing * (len(self.timesteps) / steps)
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bsmntw_weighing = bsmntw_weighing + bsmntw_weighing[1]
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self.linear_timesteps_weights = bsmntw_weighing
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def step(self, model_output, timestep, sample, to_final: bool = False, eta: float = 0.0, **kwargs):
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"""
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DDIM step function.
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Follows FlowMatchScheduler interface: step(model_output, timestep, sample, to_final=False)
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For SD 1.5, prediction_type="epsilon" and eta=0.0 (deterministic DDIM).
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"""
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if isinstance(timestep, torch.Tensor):
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timestep = timestep.cpu()
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if timestep.dim() == 0:
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timestep = timestep.item()
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elif timestep.dim() == 1:
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timestep = timestep[0].item()
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# Ensure timestep is int
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timestep = int(timestep)
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# Find the index of the current timestep
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timestep_id = torch.argmin((self.timesteps - timestep).abs()).item()
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if timestep_id + 1 >= len(self.timesteps):
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prev_timestep = -1
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else:
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prev_timestep = self.timesteps[timestep_id + 1].item()
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# Get alphas
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alpha_prod_t = self.alphas_cumprod[timestep]
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alpha_prod_t_prev = self.alphas_cumprod[prev_timestep] if prev_timestep >= 0 else self.final_alpha_cumprod
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alpha_prod_t = alpha_prod_t.to(device=sample.device, dtype=sample.dtype)
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alpha_prod_t_prev = alpha_prod_t_prev.to(device=sample.device, dtype=sample.dtype)
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beta_prod_t = 1 - alpha_prod_t
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# Compute predicted original sample (x_0)
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def denoise(self, model_output, sample, alpha_prod_t, alpha_prod_t_prev):
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if self.prediction_type == "epsilon":
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pred_original_sample = (sample - beta_prod_t.sqrt() * model_output) / alpha_prod_t.sqrt()
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elif self.prediction_type == "sample":
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pred_original_sample = model_output
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weight_e = math.sqrt(1 - alpha_prod_t_prev) - math.sqrt(alpha_prod_t_prev * (1 - alpha_prod_t) / alpha_prod_t)
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weight_x = math.sqrt(alpha_prod_t_prev / alpha_prod_t)
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prev_sample = sample * weight_x + model_output * weight_e
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elif self.prediction_type == "v_prediction":
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pred_original_sample = alpha_prod_t.sqrt() * sample - beta_prod_t.sqrt() * model_output
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weight_e = -math.sqrt(alpha_prod_t_prev * (1 - alpha_prod_t)) + math.sqrt(alpha_prod_t * (1 - alpha_prod_t_prev))
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weight_x = math.sqrt(alpha_prod_t * alpha_prod_t_prev) + math.sqrt((1 - alpha_prod_t) * (1 - alpha_prod_t_prev))
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prev_sample = sample * weight_x + model_output * weight_e
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else:
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raise ValueError(f"Unsupported prediction_type: {self.prediction_type}")
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# Clip sample if needed
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if self.clip_sample:
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pred_original_sample = pred_original_sample.clamp(-1.0, 1.0)
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# Compute predicted noise (re-derived from x_0)
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pred_epsilon = (sample - alpha_prod_t.sqrt() * pred_original_sample) / beta_prod_t.sqrt()
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# DDIM formula: prev_sample = sqrt(alpha_prev) * x0 + sqrt(1 - alpha_prev) * epsilon
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prev_sample = alpha_prod_t_prev.sqrt() * pred_original_sample + (1 - alpha_prod_t_prev).sqrt() * pred_epsilon
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# Add variance noise if eta > 0 (DDIM: eta=0, DDPM: eta=1)
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if eta > 0:
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variance = self._get_variance(timestep, prev_timestep)
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variance = variance.to(device=sample.device, dtype=sample.dtype)
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std_dev_t = eta * variance.sqrt()
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device = sample.device
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noise = torch.randn_like(sample)
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prev_sample = prev_sample + std_dev_t * noise
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raise NotImplementedError(f"{self.prediction_type} is not implemented")
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return prev_sample
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def add_noise(self, original_samples, noise, timestep):
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"""Add noise to original samples (forward diffusion).
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Follows FlowMatchScheduler interface: add_noise(original_samples, noise, timestep)
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"""
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def step(self, model_output, timestep, sample, to_final=False):
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alpha_prod_t = self.alphas_cumprod[int(timestep.flatten().tolist()[0])]
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if isinstance(timestep, torch.Tensor):
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timestep = timestep.cpu()
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if timestep.dim() == 0:
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timestep = timestep.item()
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elif timestep.dim() == 1:
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timestep = timestep[0].item()
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timestep_id = torch.argmin((self.timesteps - timestep).abs())
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if to_final or timestep_id + 1 >= len(self.timesteps):
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alpha_prod_t_prev = 1.0
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else:
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timestep_prev = int(self.timesteps[timestep_id + 1])
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alpha_prod_t_prev = self.alphas_cumprod[timestep_prev]
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timestep = int(timestep)
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# Defensive clamp: ensure timestep is within valid range
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timestep = max(0, min(timestep, self.num_train_timesteps - 1))
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sqrt_alpha_prod = self.alphas_cumprod[timestep].sqrt()
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sqrt_one_minus_alpha_prod = (1 - self.alphas_cumprod[timestep]).sqrt()
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return self.denoise(model_output, sample, alpha_prod_t, alpha_prod_t_prev)
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sqrt_alpha_prod = sqrt_alpha_prod.to(device=original_samples.device, dtype=original_samples.dtype)
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sqrt_one_minus_alpha_prod = sqrt_one_minus_alpha_prod.to(device=original_samples.device, dtype=original_samples.dtype)
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# Handle broadcasting for batch timesteps
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while sqrt_alpha_prod.dim() < original_samples.dim():
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sqrt_alpha_prod = sqrt_alpha_prod.unsqueeze(-1)
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sqrt_one_minus_alpha_prod = sqrt_one_minus_alpha_prod.unsqueeze(-1)
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sample = sqrt_alpha_prod * original_samples + sqrt_one_minus_alpha_prod * noise
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return sample
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def return_to_timestep(self, timestep, sample, sample_stablized):
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alpha_prod_t = self.alphas_cumprod[int(timestep.flatten().tolist()[0])]
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noise_pred = (sample - math.sqrt(alpha_prod_t) * sample_stablized) / math.sqrt(1 - alpha_prod_t)
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return noise_pred
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def add_noise(self, original_samples, noise, timestep):
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sqrt_alpha_prod = math.sqrt(self.alphas_cumprod[int(timestep.flatten().tolist()[0])])
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sqrt_one_minus_alpha_prod = math.sqrt(1 - self.alphas_cumprod[int(timestep.flatten().tolist()[0])])
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noisy_samples = sqrt_alpha_prod * original_samples + sqrt_one_minus_alpha_prod * noise
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return noisy_samples
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def training_target(self, sample, noise, timestep):
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"""Return the training target for the given prediction type."""
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if isinstance(timestep, torch.Tensor):
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timestep = timestep.cpu()
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if timestep.dim() == 0:
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timestep = timestep.item()
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elif timestep.dim() == 1:
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timestep = timestep[0].item()
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timestep = int(timestep)
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timestep = max(0, min(timestep, self.num_train_timesteps - 1))
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if self.prediction_type == "epsilon":
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return noise
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elif self.prediction_type == "v_prediction":
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sqrt_alpha_prod = self.alphas_cumprod[timestep].sqrt()
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sqrt_one_minus_alpha_prod = (1 - self.alphas_cumprod[timestep]).sqrt()
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return sqrt_alpha_prod * noise - sqrt_one_minus_alpha_prod * sample
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elif self.prediction_type == "sample":
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return sample
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else:
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raise ValueError(f"Unsupported prediction_type: {self.prediction_type}")
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sqrt_alpha_prod = math.sqrt(self.alphas_cumprod[int(timestep.flatten().tolist()[0])])
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sqrt_one_minus_alpha_prod = math.sqrt(1 - self.alphas_cumprod[int(timestep.flatten().tolist()[0])])
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target = sqrt_alpha_prod * noise - sqrt_one_minus_alpha_prod * sample
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return target
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def training_weight(self, timestep):
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"""Return training weight for the given timestep."""
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timestep = max(0, min(int(timestep), self.num_train_timesteps - 1))
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timestep_tensor = torch.tensor(timestep, device=self.timesteps.device)
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timestep_id = torch.argmin((self.timesteps - timestep_tensor).abs())
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return self.linear_timesteps_weights[timestep_id]
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return 1.0
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