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import tqdm
import torch
from diffusers import DiffusionPipeline
# add these relative imports here, so we can load from hub
from .modeling_vae import AutoencoderKL # NOQA
from .configuration_ldmbert import LDMBertConfig # NOQA
from .modeling_ldmbert import LDMBertModel # NOQA
class LatentDiffusion(DiffusionPipeline):
def __init__(self, vqvae, bert, tokenizer, unet, noise_scheduler):
super().__init__()
self.register_modules(vqvae=vqvae, bert=bert, tokenizer=tokenizer, unet=unet, noise_scheduler=noise_scheduler)
@torch.no_grad()
def __call__(self, prompt, batch_size=1, generator=None, torch_device=None, eta=0.0, guidance_scale=1.0, num_inference_steps=50):
# eta corresponds to η in paper and should be between [0, 1]
if torch_device is None:
torch_device = "cuda" if torch.cuda.is_available() else "cpu"
self.unet.to(torch_device)
self.vqvae.to(torch_device)
self.bert.to(torch_device)
# get unconditional embeddings for classifier free guidence
if guidance_scale != 1.0:
uncond_input = self.tokenizer([""], padding="max_length", max_length=77, return_tensors='pt').to(torch_device)
uncond_embeddings = self.bert(uncond_input.input_ids)[0]
# get text embedding
text_input = self.tokenizer(prompt, padding="max_length", max_length=77, return_tensors='pt').to(torch_device)
text_embedding = self.bert(text_input.input_ids)[0]
num_trained_timesteps = self.noise_scheduler.num_timesteps
inference_step_times = range(0, num_trained_timesteps, num_trained_timesteps // num_inference_steps)
image = self.noise_scheduler.sample_noise(
(batch_size, self.unet.in_channels, self.unet.image_size, self.unet.image_size),
device=torch_device,
generator=generator,
)
# See formulas (12) and (16) of DDIM paper https://arxiv.org/pdf/2010.02502.pdf
# Ideally, read DDIM paper in-detail understanding
# Notation (<variable name> -> <name in paper>
# - pred_noise_t -> e_theta(x_t, t)
# - pred_original_image -> f_theta(x_t, t) or x_0
# - std_dev_t -> sigma_t
# - eta -> η
# - pred_image_direction -> "direction pointingc to x_t"
# - pred_prev_image -> "x_t-1"
for t in tqdm.tqdm(reversed(range(num_inference_steps)), total=num_inference_steps):
# guidance_scale of 1 means no guidance
if guidance_scale == 1.0:
image_in = image
context = text_embedding
timesteps = torch.tensor([inference_step_times[t]] * image.shape[0], device=torch_device)
else:
# for classifier free guidance, we need to do two forward passes
# here we concanate embedding and unconditioned embedding in a single batch
# to avoid doing two forward passes
image_in = torch.cat([image] * 2)
context = torch.cat([uncond_embeddings, text_embedding])
timesteps = torch.tensor([inference_step_times[t]] * image.shape[0], device=torch_device)
# 1. predict noise residual
pred_noise_t = self.unet(image_in, timesteps, context=context)
# perform guidance
if guidance_scale != 1.0:
pred_noise_t_uncond, pred_noise_t = pred_noise_t.chunk(2)
pred_noise_t = pred_noise_t_uncond + guidance_scale * (pred_noise_t - pred_noise_t_uncond)
# 2. predict previous mean of image x_t-1
pred_prev_image = self.noise_scheduler.compute_prev_image_step(pred_noise_t, image, t, num_inference_steps, eta)
# 3. optionally sample variance
variance = 0
if eta > 0:
noise = self.noise_scheduler.sample_noise(image.shape, device=image.device, generator=generator)
variance = self.noise_scheduler.get_variance(t, num_inference_steps).sqrt() * eta * noise
# 4. set current image to prev_image: x_t -> x_t-1
image = pred_prev_image + variance
# scale and decode image with vae
image = 1 / 0.18215 * image
image = self.vqvae.decode(image)
image = torch.clamp((image+1.0)/2.0, min=0.0, max=1.0)
return image
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