Walk between stable diffusion text prompts

stable_diffusion_walk.py

"""
Built on top of this gist by @karpathy:
https://gist.github.com/karpathy/00103b0037c5aaea32fe1da1af553355

stable diffusion dreaming over text prompts
creates hypnotic moving videos by smoothly walking randomly through the sample space

example way to run this script:
$ python stable_diffusion_walk.py --prompts "['blueberry spaghetti', 'strawberry spaghetti']" --seeds 243,523 --name berry_good_spaghetti

to stitch together the images, e.g.:
$ ffmpeg -r 10 -f image2 -s 512x512 -i dreams/berry_good_spaghetti/frame%06d.jpg -vcodec libx264 -crf 10 -pix_fmt yuv420p berry_good_spaghetti.mp4

nice slerp def from @xsteenbrugge ty
you have to have access to stablediffusion checkpoints from https://huggingface.co/CompVis
and install all the other dependencies (e.g. diffusers library)
"""

import os
import inspect
import fire
from diffusers import StableDiffusionPipeline
from diffusers.schedulers import DDIMScheduler, LMSDiscreteScheduler, PNDMScheduler
from time import time
from PIL import Image
from einops import rearrange
import numpy as np
import torch
from torch import autocast
from torchvision.utils import make_grid

# -----------------------------------------------------------------------------

@torch.no_grad()
def diffuse(
        pipe,
        cond_embeddings, # text conditioning, should be (1, 77, 768)
        cond_latents,    # image conditioning, should be (1, 4, 64, 64)
        num_inference_steps,
        guidance_scale,
        eta,
    ):
    torch_device = cond_latents.get_device()

    # classifier guidance: add the unconditional embedding
    max_length = cond_embeddings.shape[1] # 77
    uncond_input = pipe.tokenizer([""], padding="max_length", max_length=max_length, return_tensors="pt")
    uncond_embeddings = pipe.text_encoder(uncond_input.input_ids.to(torch_device))[0]
    text_embeddings = torch.cat([uncond_embeddings, cond_embeddings])

    # if we use LMSDiscreteScheduler, let's make sure latents are mulitplied by sigmas
    if isinstance(pipe.scheduler, LMSDiscreteScheduler):
        cond_latents = cond_latents * pipe.scheduler.sigmas[0]

    # init the scheduler
    accepts_offset = "offset" in set(inspect.signature(pipe.scheduler.set_timesteps).parameters.keys())
    extra_set_kwargs = {}
    if accepts_offset:
        extra_set_kwargs["offset"] = 1
    pipe.scheduler.set_timesteps(num_inference_steps, **extra_set_kwargs)
    # prepare extra kwargs for the scheduler step, since not all schedulers have the same signature
    # eta (η) is only used with the DDIMScheduler, it will be ignored for other schedulers.
    # eta corresponds to η in DDIM paper: https://arxiv.org/abs/2010.02502
    # and should be between [0, 1]
    accepts_eta = "eta" in set(inspect.signature(pipe.scheduler.step).parameters.keys())
    extra_step_kwargs = {}
    if accepts_eta:
        extra_step_kwargs["eta"] = eta

    # diffuse!
    for i, t in enumerate(pipe.scheduler.timesteps):

        # expand the latents for classifier free guidance
        # TODO: gross much???
        latent_model_input = torch.cat([cond_latents] * 2)
        if isinstance(pipe.scheduler, LMSDiscreteScheduler):
            sigma = pipe.scheduler.sigmas[i]
            latent_model_input = latent_model_input / ((sigma**2 + 1) ** 0.5)

        # predict the noise residual
        noise_pred = pipe.unet(latent_model_input, t, encoder_hidden_states=text_embeddings)["sample"]

        # cfg
        noise_pred_uncond, noise_pred_text = noise_pred.chunk(2)
        noise_pred = noise_pred_uncond + guidance_scale * (noise_pred_text - noise_pred_uncond)

        # compute the previous noisy sample x_t -> x_t-1
        # TODO: omfg...
        if isinstance(pipe.scheduler, LMSDiscreteScheduler):
            cond_latents = pipe.scheduler.step(noise_pred, i, cond_latents, **extra_step_kwargs)["prev_sample"]
        else:
            cond_latents = pipe.scheduler.step(noise_pred, t, cond_latents, **extra_step_kwargs)["prev_sample"]

    # scale and decode the image latents with vae
    cond_latents = 1 / 0.18215 * cond_latents
    image = pipe.vae.decode(cond_latents)

    # generate output numpy image as uint8
    image = (image / 2 + 0.5).clamp(0, 1)
    image = image.cpu().permute(0, 2, 3, 1).numpy()
    image = (image[0] * 255).astype(np.uint8)

    return image

def slerp(t, v0, v1, DOT_THRESHOLD=0.9995):
    """ helper function to spherically interpolate two arrays v1 v2 """

    if not isinstance(v0, np.ndarray):
        inputs_are_torch = True
        input_device = v0.device
        v0 = v0.cpu().numpy()
        v1 = v1.cpu().numpy()

    dot = np.sum(v0 * v1 / (np.linalg.norm(v0) * np.linalg.norm(v1)))
    if np.abs(dot) > DOT_THRESHOLD:
        v2 = (1 - t) * v0 + t * v1
    else:
        theta_0 = np.arccos(dot)
        sin_theta_0 = np.sin(theta_0)
        theta_t = theta_0 * t
        sin_theta_t = np.sin(theta_t)
        s0 = np.sin(theta_0 - theta_t) / sin_theta_0
        s1 = sin_theta_t / sin_theta_0
        v2 = s0 * v0 + s1 * v1

    if inputs_are_torch:
        v2 = torch.from_numpy(v2).to(input_device)

    return v2

def main(
        # --------------------------------------
        # args you probably want to change
        prompts = ["blueberry spaghetti", "strawberry spaghetti"], # prompts to dream about
        seeds=[243, 523],
        gpu = 0, # id of the gpu to run on
        name = 'berry_good_spaghetti', # name of this project, for the output directory
        rootdir = './dreams',
        num_steps = 72,  # number of steps between each pair of sampled points
        # --------------------------------------
        # args you probably don't want to change
        num_inference_steps = 50,
        guidance_scale = 7.5,
        eta = 0.0,
        width = 512,
        height = 512,
        # --------------------------------------
):
    assert len(prompts) == len(seeds)
    assert torch.cuda.is_available()
    assert height % 8 == 0 and width % 8 == 0

    # init the output dir
    outdir = os.path.join(rootdir, name)
    os.makedirs(outdir, exist_ok=True)

    # # init all of the models and move them to a given GPU
    pipe = StableDiffusionPipeline.from_pretrained("CompVis/stable-diffusion-v1-3-diffusers", use_auth_token=True)
    torch_device = f"cuda:{gpu}"
    pipe.unet.to(torch_device)
    pipe.vae.to(torch_device)
    pipe.text_encoder.to(torch_device)

    # get the conditional text embeddings based on the prompts
    prompt_embeddings = []
    for prompt in prompts:   
        text_input = pipe.tokenizer(
            prompt,
            padding="max_length",
            max_length=pipe.tokenizer.model_max_length,
            truncation=True,
            return_tensors="pt"
        )
        with torch.no_grad():
            embed = pipe.text_encoder(text_input.input_ids.to(torch_device))[0]

        prompt_embeddings.append(embed)
    
    # Take first embed and set it as starting point, leaving rest as list we'll loop over.
    prompt_embedding_a, *prompt_embeddings = prompt_embeddings

    # Take first seed and use it to generate init noise
    init_seed, *seeds = seeds
    init_a = torch.randn(
        (1, pipe.unet.in_channels, height // 8, width // 8),
        device=torch_device,
        generator=torch.Generator(device='cuda').manual_seed(init_seed)
    )
    
    frame_index = 0
    for p, prompt_embedding_b in enumerate(prompt_embeddings):

        init_b = torch.randn(
            (1, pipe.unet.in_channels, height // 8, width // 8),
            generator=torch.Generator(device='cuda').manual_seed(seeds[p]),
            device=torch_device
        )

        for i, t in enumerate(np.linspace(0, 1, num_steps)):
            print("dreaming... ", frame_index)

            cond_embedding = slerp(float(t), prompt_embedding_a, prompt_embedding_b)
            init = slerp(float(t), init_a, init_b)

            with autocast("cuda"):
                image = diffuse(pipe, cond_embedding, init, num_inference_steps, guidance_scale, eta)

            im = Image.fromarray(image)
            outpath = os.path.join(outdir, 'frame%06d.jpg' % frame_index)
            im.save(outpath)
            frame_index += 1

        prompt_embedding_a = prompt_embedding_b
        init_a = init_b


if __name__ == '__main__':
    fire.Fire(main)

I've found that slerp is necessary for good results when interpolating between initial latents like the base for this, but for prompt embeddings a good old torch.lerp may wind up doing more of what you want, especially when interpolating between related prompts. e.g. "a lion in a grassy meadow" -> "a bear in a grassy meadow" tends to keep the meadow the whole way through when lerped, but slerping will often find a path where the meadow disappears in the middle

@apage43 Thanks so much for the tip!! Will give it a go myself (when I get the chance) and report back here with findings. If its objectively better, I'll update this gist to use it...this gist also needs to be updated for the newer releases of stable diffusion, so I'll try to do both updates at once.

Update here - I ended up editing the diffusers pipeline to accept text_embeddings as an optional parameter to override the prompt. Then performed the walk as seen above. Will update here when I share that (perhaps will be in a github repo with an accompanying Gradio demo instead of the gist, since its more than one file now).

Ok final update - I moved all the code to this repo, where you can even run this in Google Colab.