| """ | |
| The following code is copied from https://github.com/modelscope/DiffSynth-Studio/blob/main/diffsynth/schedulers/flow_match.py | |
| """ | |
| import torch | |
| class FlowMatchScheduler(): | |
| def __init__(self, num_inference_steps=100, num_train_timesteps=1000, shift=3.0, sigma_max=1.0, sigma_min=0.003 / 1.002, inverse_timesteps=False, extra_one_step=False, reverse_sigmas=False): | |
| self.num_train_timesteps = num_train_timesteps | |
| self.shift = shift | |
| self.sigma_max = sigma_max | |
| self.sigma_min = sigma_min | |
| self.inverse_timesteps = inverse_timesteps | |
| self.extra_one_step = extra_one_step | |
| self.reverse_sigmas = reverse_sigmas | |
| self.set_timesteps(num_inference_steps) | |
| def set_timesteps(self, num_inference_steps=100, denoising_strength=1.0, training=False): | |
| sigma_start = self.sigma_min + \ | |
| (self.sigma_max - self.sigma_min) * denoising_strength | |
| if self.extra_one_step: | |
| self.sigmas = torch.linspace( | |
| sigma_start, self.sigma_min, num_inference_steps + 1)[:-1] | |
| else: | |
| self.sigmas = torch.linspace( | |
| sigma_start, self.sigma_min, num_inference_steps) | |
| if self.inverse_timesteps: | |
| self.sigmas = torch.flip(self.sigmas, dims=[0]) | |
| self.sigmas = self.shift * self.sigmas / \ | |
| (1 + (self.shift - 1) * self.sigmas) | |
| if self.reverse_sigmas: | |
| self.sigmas = 1 - self.sigmas | |
| self.timesteps = self.sigmas * self.num_train_timesteps | |
| if training: | |
| x = self.timesteps | |
| y = torch.exp(-2 * ((x - num_inference_steps / 2) / | |
| num_inference_steps) ** 2) | |
| y_shifted = y - y.min() | |
| bsmntw_weighing = y_shifted * \ | |
| (num_inference_steps / y_shifted.sum()) | |
| self.linear_timesteps_weights = bsmntw_weighing | |
| def step(self, model_output, timestep, sample, to_final=False): | |
| self.sigmas = self.sigmas.to(model_output.device) | |
| self.timesteps = self.timesteps.to(model_output.device) | |
| timestep_id = torch.argmin( | |
| (self.timesteps - timestep).abs(), dim=0) | |
| sigma = self.sigmas[timestep_id].reshape(-1, 1, 1, 1) | |
| if to_final or (timestep_id + 1 >= len(self.timesteps)).any(): | |
| sigma_ = 1 if ( | |
| self.inverse_timesteps or self.reverse_sigmas) else 0 | |
| else: | |
| sigma_ = self.sigmas[timestep_id + 1].reshape(-1, 1, 1, 1) | |
| prev_sample = sample + model_output * (sigma_ - sigma) | |
| return prev_sample | |
| def add_noise(self, original_samples, noise, timestep): | |
| """ | |
| Diffusion forward corruption process. | |
| Input: | |
| - clean_latent: the clean latent with shape [B, C, H, W] | |
| - noise: the noise with shape [B, C, H, W] | |
| - timestep: the timestep with shape [B] | |
| Output: the corrupted latent with shape [B, C, H, W] | |
| """ | |
| self.sigmas = self.sigmas.to(noise.device) | |
| self.timesteps = self.timesteps.to(noise.device) | |
| timestep_id = torch.argmin( | |
| (self.timesteps.unsqueeze(0) - timestep.unsqueeze(1)).abs(), dim=1) | |
| sigma = self.sigmas[timestep_id].reshape(-1, 1, 1, 1) | |
| sample = (1 - sigma) * original_samples + sigma * noise | |
| return sample.type_as(noise) | |
| def training_target(self, sample, noise, timestep): | |
| target = noise - sample | |
| return target | |
| def training_weight(self, timestep): | |
| timestep_id = torch.argmin( | |
| (self.timesteps - timestep.to(self.timesteps.device)).abs()) | |
| weights = self.linear_timesteps_weights[timestep_id] | |
| return weights |