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High-Resolution Image Synthesis with Latent Diffusion Models

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High-Resolution Image Synthesis with Latent Diffusion Models

Quick Overview

Latent Diffusion is a high-resolution image synthesis framework developed by CompVis. It uses a two-stage approach: first compressing images into a latent space, then applying diffusion models in this compressed space. This method allows for efficient generation of high-quality images while reducing computational requirements.

Pros

  • Enables high-resolution image generation with reduced computational costs
  • Produces high-quality, detailed images
  • Versatile framework applicable to various image synthesis tasks
  • Allows for controllable image generation through conditioning

Cons

  • Requires significant GPU resources for training and inference
  • Complex architecture may be challenging to understand and implement
  • Limited documentation and examples for beginners
  • May require fine-tuning for specific use cases

Code Examples

# Load a pre-trained Latent Diffusion model
model = LatentDiffusion.from_pretrained("CompVis/ldm-text2im-large-256")

# Generate an image from text prompt
prompt = "A beautiful sunset over the ocean"
image = model.generate(prompt)
image.save("sunset.png")
# Perform image-to-image translation
source_image = Image.open("source.png")
target_prompt = "Convert this image to an oil painting style"
translated_image = model.translate(source_image, target_prompt)
translated_image.save("oil_painting.png")
# Fine-tune the model on a custom dataset
custom_dataset = CustomImageDataset("path/to/dataset")
model.fine_tune(custom_dataset, epochs=10, learning_rate=1e-5)

Getting Started

To get started with Latent Diffusion:

  1. Install the required dependencies:
pip install torch torchvision transformers
git clone https://github.com/CompVis/latent-diffusion.git
cd latent-diffusion
pip install -e .
  1. Download a pre-trained model:
from latent_diffusion import LatentDiffusion

model = LatentDiffusion.from_pretrained("CompVis/ldm-text2im-large-256")
  1. Generate an image:
prompt = "A futuristic cityscape at night"
image = model.generate(prompt)
image.save("cityscape.png")

Competitor Comparisons

25,061

🤗 Diffusers: State-of-the-art diffusion models for image and audio generation in PyTorch and FLAX.

Pros of diffusers

  • More user-friendly and easier to integrate into existing projects
  • Offers a wider range of pre-trained models and pipelines
  • Actively maintained with frequent updates and community support

Cons of diffusers

  • May have slightly higher computational overhead due to abstraction layers
  • Less flexibility for low-level customization of the diffusion process

Code comparison

latent-diffusion:

model = LatentDiffusion(
    linear_start=0.00085,
    linear_end=0.0120,
    num_timesteps=1000,
    latent_channels=4,
    channels=128,
    channel_mult=[1, 2, 4, 4],
)

diffusers:

from diffusers import StableDiffusionPipeline

pipeline = StableDiffusionPipeline.from_pretrained("runwayml/stable-diffusion-v1-5")
image = pipeline("A beautiful sunset over the ocean").images[0]

The latent-diffusion code focuses on model initialization, while diffusers provides a higher-level API for easy use of pre-trained models and generation pipelines.

10,774

PyTorch package for the discrete VAE used for DALL·E.

Pros of DALL-E

  • More advanced and capable of generating highly detailed and diverse images
  • Trained on a larger dataset, resulting in better understanding of complex concepts
  • Produces higher resolution outputs with better coherence and consistency

Cons of DALL-E

  • Closed-source, limiting accessibility and customization options
  • Requires significant computational resources for training and inference
  • Less flexibility in terms of model architecture and fine-tuning

Code Comparison

While both repositories are focused on image generation, their codebases differ significantly. Here's a brief comparison of their image generation functions:

DALL-E:

def generate_images(prompt, num_images=1):
    return model.generate(prompt, num_images)

Latent-diffusion:

def generate_images(prompt, num_images=1):
    latents = model.encode(prompt)
    return model.decode(latents, num_samples=num_images)

Latent-diffusion uses a two-step process of encoding and decoding, while DALL-E's approach is more direct. However, due to DALL-E being closed-source, the actual implementation details are not publicly available.

Implementation of Denoising Diffusion Probabilistic Model in Pytorch

Pros of denoising-diffusion-pytorch

  • Simpler implementation, making it easier to understand and modify
  • More focused on the core diffusion process, without additional complexities
  • Potentially faster training and inference due to its streamlined approach

Cons of denoising-diffusion-pytorch

  • Less feature-rich compared to latent-diffusion
  • May not achieve the same level of image quality as latent-diffusion
  • Limited to basic diffusion models without advanced techniques like latent space compression

Code Comparison

latent-diffusion:

def forward(self, x, t, c):
    t_emb = timestep_embedding(t, self.model_channels)
    emb = self.time_embed(t_emb)
    h = x.type(self.dtype)
    for module in self.input_blocks:
        h = module(h, emb, c)
    h = self.middle_block(h, emb, c)

denoising-diffusion-pytorch:

def forward(self, x, time):
    x = self.init_conv(x)
    r = x.clone()
    for block in self.blocks:
        x = block(x, time)
    return self.final_conv(x) + r

The code comparison shows that latent-diffusion has a more complex forward pass, incorporating conditioning and multiple input blocks, while denoising-diffusion-pytorch has a simpler structure with a single loop over blocks.

Karras et al. (2022) diffusion models for PyTorch

Pros of k-diffusion

  • More flexible and customizable diffusion models
  • Supports a wider range of sampling methods
  • Better performance on certain tasks, especially with fewer sampling steps

Cons of k-diffusion

  • Less extensive documentation compared to latent-diffusion
  • Smaller community and fewer pre-trained models available
  • May require more expertise to implement and fine-tune effectively

Code Comparison

k-diffusion:

model = diffusion.DiffusionModel(
    unet, sigma_data=1.0, sigma_min=0.02, sigma_max=100
)
x = torch.randn(4, 3, 64, 64)
x = diffusion.sample(model, x, steps=20, clip_denoised=True)

latent-diffusion:

model = LatentDiffusion.from_pretrained("CompVis/ldm-text2im-large-256")
prompt = ["a painting of a cat"]
images = model(prompt, num_inference_steps=50, guidance_scale=7.5)

Both repositories offer diffusion-based image generation models, but k-diffusion provides more flexibility in model architecture and sampling methods. latent-diffusion, on the other hand, offers a more user-friendly interface and a larger selection of pre-trained models. The code examples demonstrate the different approaches: k-diffusion allows for more low-level control, while latent-diffusion provides a higher-level API for easier use.

High-Resolution Image Synthesis with Latent Diffusion Models

Pros of stablediffusion

  • More advanced and refined implementation of the latent diffusion model
  • Includes additional features like inpainting and image-to-image translation
  • Better documentation and community support

Cons of stablediffusion

  • Larger model size, requiring more computational resources
  • More complex codebase, potentially harder for beginners to understand
  • Stricter licensing terms compared to latent-diffusion

Code Comparison

latent-diffusion:

model = LatentDiffusion(
    linear_start=0.0015,
    linear_end=0.0195,
    n_steps=1000,
    latent_channels=4
)

stablediffusion:

model = StableDiffusion(
    unet_config={
        "target": "ldm.modules.diffusionmodules.openaimodel.UNetModel",
        "params": {
            "image_size": 32,
            "in_channels": 4,
            "out_channels": 4,
            "model_channels": 320,
            "attention_resolutions": [4, 2, 1],
            "num_res_blocks": 2,
            "channel_mult": [1, 2, 4, 4],
            "num_heads": 8,
            "use_spatial_transformer": True,
            "transformer_depth": 1,
            "context_dim": 768,
            "use_checkpoint": True,
            "legacy": False,
        },
    },
)

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README

Latent Diffusion Models

arXiv | BibTeX

High-Resolution Image Synthesis with Latent Diffusion Models
Robin Rombach*, Andreas Blattmann*, Dominik Lorenz, Patrick Esser, Björn Ommer
* equal contribution

News

July 2022

April 2022

Requirements

A suitable conda environment named ldm can be created and activated with:

conda env create -f environment.yaml
conda activate ldm

Pretrained Models

A general list of all available checkpoints is available in via our model zoo. If you use any of these models in your work, we are always happy to receive a citation.

Retrieval Augmented Diffusion Models

rdm-figure We include inference code to run our retrieval-augmented diffusion models (RDMs) as described in https://arxiv.org/abs/2204.11824.

To get started, install the additionally required python packages into your ldm environment

pip install transformers==4.19.2 scann kornia==0.6.4 torchmetrics==0.6.0
pip install git+https://github.com/arogozhnikov/einops.git

and download the trained weights (preliminary ceckpoints):

mkdir -p models/rdm/rdm768x768/
wget -O models/rdm/rdm768x768/model.ckpt https://ommer-lab.com/files/rdm/model.ckpt

As these models are conditioned on a set of CLIP image embeddings, our RDMs support different inference modes, which are described in the following.

RDM with text-prompt only (no explicit retrieval needed)

Since CLIP offers a shared image/text feature space, and RDMs learn to cover a neighborhood of a given example during training, we can directly take a CLIP text embedding of a given prompt and condition on it. Run this mode via

python scripts/knn2img.py  --prompt "a happy bear reading a newspaper, oil on canvas"

RDM with text-to-image retrieval

To be able to run a RDM conditioned on a text-prompt and additionally images retrieved from this prompt, you will also need to download the corresponding retrieval database. We provide two distinct databases extracted from the Openimages- and ArtBench- datasets. Interchanging the databases results in different capabilities of the model as visualized below, although the learned weights are the same in both cases.

Download the retrieval-databases which contain the retrieval-datasets (Openimages (~11GB) and ArtBench (~82MB)) compressed into CLIP image embeddings:

mkdir -p data/rdm/retrieval_databases
wget -O data/rdm/retrieval_databases/artbench.zip https://ommer-lab.com/files/rdm/artbench_databases.zip
wget -O data/rdm/retrieval_databases/openimages.zip https://ommer-lab.com/files/rdm/openimages_database.zip
unzip data/rdm/retrieval_databases/artbench.zip -d data/rdm/retrieval_databases/
unzip data/rdm/retrieval_databases/openimages.zip -d data/rdm/retrieval_databases/

We also provide trained ScaNN search indices for ArtBench. Download and extract via

mkdir -p data/rdm/searchers
wget -O data/rdm/searchers/artbench.zip https://ommer-lab.com/files/rdm/artbench_searchers.zip
unzip data/rdm/searchers/artbench.zip -d data/rdm/searchers

Since the index for OpenImages is large (~21 GB), we provide a script to create and save it for usage during sampling. Note however, that sampling with the OpenImages database will not be possible without this index. Run the script via

python scripts/train_searcher.py

Retrieval based text-guided sampling with visual nearest neighbors can be started via

python scripts/knn2img.py  --prompt "a happy pineapple" --use_neighbors --knn <number_of_neighbors> 

Note that the maximum supported number of neighbors is 20. The database can be changed via the cmd parameter --database which can be [openimages, artbench-art_nouveau, artbench-baroque, artbench-expressionism, artbench-impressionism, artbench-post_impressionism, artbench-realism, artbench-renaissance, artbench-romanticism, artbench-surrealism, artbench-ukiyo_e]. For using --database openimages, the above script (scripts/train_searcher.py) must be executed before. Due to their relatively small size, the artbench datasetbases are best suited for creating more abstract concepts and do not work well for detailed text control.

Coming Soon

  • better models
  • more resolutions
  • image-to-image retrieval

Text-to-Image

text2img-figure

Download the pre-trained weights (5.7GB)

mkdir -p models/ldm/text2img-large/
wget -O models/ldm/text2img-large/model.ckpt https://ommer-lab.com/files/latent-diffusion/nitro/txt2img-f8-large/model.ckpt

and sample with

python scripts/txt2img.py --prompt "a virus monster is playing guitar, oil on canvas" --ddim_eta 0.0 --n_samples 4 --n_iter 4 --scale 5.0  --ddim_steps 50

This will save each sample individually as well as a grid of size n_iter x n_samples at the specified output location (default: outputs/txt2img-samples). Quality, sampling speed and diversity are best controlled via the scale, ddim_steps and ddim_eta arguments. As a rule of thumb, higher values of scale produce better samples at the cost of a reduced output diversity.
Furthermore, increasing ddim_steps generally also gives higher quality samples, but returns are diminishing for values > 250. Fast sampling (i.e. low values of ddim_steps) while retaining good quality can be achieved by using --ddim_eta 0.0.
Faster sampling (i.e. even lower values of ddim_steps) while retaining good quality can be achieved by using --ddim_eta 0.0 and --plms (see Pseudo Numerical Methods for Diffusion Models on Manifolds).

Beyond 256²

For certain inputs, simply running the model in a convolutional fashion on larger features than it was trained on can sometimes result in interesting results. To try it out, tune the H and W arguments (which will be integer-divided by 8 in order to calculate the corresponding latent size), e.g. run

python scripts/txt2img.py --prompt "a sunset behind a mountain range, vector image" --ddim_eta 1.0 --n_samples 1 --n_iter 1 --H 384 --W 1024 --scale 5.0  

to create a sample of size 384x1024. Note, however, that controllability is reduced compared to the 256x256 setting.

The example below was generated using the above command. text2img-figure-conv

Inpainting

inpainting

Download the pre-trained weights

wget -O models/ldm/inpainting_big/last.ckpt https://heibox.uni-heidelberg.de/f/4d9ac7ea40c64582b7c9/?dl=1

and sample with

python scripts/inpaint.py --indir data/inpainting_examples/ --outdir outputs/inpainting_results

indir should contain images *.png and masks <image_fname>_mask.png like the examples provided in data/inpainting_examples.

Class-Conditional ImageNet

Available via a notebook . class-conditional

Unconditional Models

We also provide a script for sampling from unconditional LDMs (e.g. LSUN, FFHQ, ...). Start it via

CUDA_VISIBLE_DEVICES=<GPU_ID> python scripts/sample_diffusion.py -r models/ldm/<model_spec>/model.ckpt -l <logdir> -n <\#samples> --batch_size <batch_size> -c <\#ddim steps> -e <\#eta> 

Train your own LDMs

Data preparation

Faces

For downloading the CelebA-HQ and FFHQ datasets, proceed as described in the taming-transformers repository.

LSUN

The LSUN datasets can be conveniently downloaded via the script available here. We performed a custom split into training and validation images, and provide the corresponding filenames at https://ommer-lab.com/files/lsun.zip. After downloading, extract them to ./data/lsun. The beds/cats/churches subsets should also be placed/symlinked at ./data/lsun/bedrooms/./data/lsun/cats/./data/lsun/churches, respectively.

ImageNet

The code will try to download (through Academic Torrents) and prepare ImageNet the first time it is used. However, since ImageNet is quite large, this requires a lot of disk space and time. If you already have ImageNet on your disk, you can speed things up by putting the data into ${XDG_CACHE}/autoencoders/data/ILSVRC2012_{split}/data/ (which defaults to ~/.cache/autoencoders/data/ILSVRC2012_{split}/data/), where {split} is one of train/validation. It should have the following structure:

${XDG_CACHE}/autoencoders/data/ILSVRC2012_{split}/data/
├── n01440764
│   ├── n01440764_10026.JPEG
│   ├── n01440764_10027.JPEG
│   ├── ...
├── n01443537
│   ├── n01443537_10007.JPEG
│   ├── n01443537_10014.JPEG
│   ├── ...
├── ...

If you haven't extracted the data, you can also place ILSVRC2012_img_train.tar/ILSVRC2012_img_val.tar (or symlinks to them) into ${XDG_CACHE}/autoencoders/data/ILSVRC2012_train/ / ${XDG_CACHE}/autoencoders/data/ILSVRC2012_validation/, which will then be extracted into above structure without downloading it again. Note that this will only happen if neither a folder ${XDG_CACHE}/autoencoders/data/ILSVRC2012_{split}/data/ nor a file ${XDG_CACHE}/autoencoders/data/ILSVRC2012_{split}/.ready exist. Remove them if you want to force running the dataset preparation again.

Model Training

Logs and checkpoints for trained models are saved to logs/<START_DATE_AND_TIME>_<config_spec>.

Training autoencoder models

Configs for training a KL-regularized autoencoder on ImageNet are provided at configs/autoencoder. Training can be started by running

CUDA_VISIBLE_DEVICES=<GPU_ID> python main.py --base configs/autoencoder/<config_spec>.yaml -t --gpus 0,    

where config_spec is one of {autoencoder_kl_8x8x64(f=32, d=64), autoencoder_kl_16x16x16(f=16, d=16), autoencoder_kl_32x32x4(f=8, d=4), autoencoder_kl_64x64x3(f=4, d=3)}.

For training VQ-regularized models, see the taming-transformers repository.

Training LDMs

In configs/latent-diffusion/ we provide configs for training LDMs on the LSUN-, CelebA-HQ, FFHQ and ImageNet datasets. Training can be started by running

CUDA_VISIBLE_DEVICES=<GPU_ID> python main.py --base configs/latent-diffusion/<config_spec>.yaml -t --gpus 0,

where <config_spec> is one of {celebahq-ldm-vq-4(f=4, VQ-reg. autoencoder, spatial size 64x64x3),ffhq-ldm-vq-4(f=4, VQ-reg. autoencoder, spatial size 64x64x3), lsun_bedrooms-ldm-vq-4(f=4, VQ-reg. autoencoder, spatial size 64x64x3), lsun_churches-ldm-vq-4(f=8, KL-reg. autoencoder, spatial size 32x32x4),cin-ldm-vq-8(f=8, VQ-reg. autoencoder, spatial size 32x32x4)}.

Model Zoo

Pretrained Autoencoding Models

rec2

All models were trained until convergence (no further substantial improvement in rFID).

ModelrFID vs valtrain stepsPSNRPSIMLinkComments
f=4, VQ (Z=8192, d=3)0.5853306627.43 +/- 4.260.53 +/- 0.21https://ommer-lab.com/files/latent-diffusion/vq-f4.zip
f=4, VQ (Z=8192, d=3)1.0665813125.21 +/- 4.170.72 +/- 0.26https://heibox.uni-heidelberg.de/f/9c6681f64bb94338a069/?dl=1no attention
f=8, VQ (Z=16384, d=4)1.1497104323.07 +/- 3.991.17 +/- 0.36https://ommer-lab.com/files/latent-diffusion/vq-f8.zip
f=8, VQ (Z=256, d=4)1.49160864922.35 +/- 3.811.26 +/- 0.37https://ommer-lab.com/files/latent-diffusion/vq-f8-n256.zip
f=16, VQ (Z=16384, d=8)5.15110116620.83 +/- 3.611.73 +/- 0.43https://heibox.uni-heidelberg.de/f/0e42b04e2e904890a9b6/?dl=1
f=4, KL0.2717699127.53 +/- 4.540.55 +/- 0.24https://ommer-lab.com/files/latent-diffusion/kl-f4.zip
f=8, KL0.9024680324.19 +/- 4.191.02 +/- 0.35https://ommer-lab.com/files/latent-diffusion/kl-f8.zip
f=16, KL (d=16)0.8744299824.08 +/- 4.221.07 +/- 0.36https://ommer-lab.com/files/latent-diffusion/kl-f16.zip
f=32, KL (d=64)2.0440676322.27 +/- 3.931.41 +/- 0.40https://ommer-lab.com/files/latent-diffusion/kl-f32.zip

Get the models

Running the following script downloads und extracts all available pretrained autoencoding models.

bash scripts/download_first_stages.sh

The first stage models can then be found in models/first_stage_models/<model_spec>

Pretrained LDMs

DatsetTaskModelFIDISPrecRecallLinkComments
CelebA-HQUnconditional Image SynthesisLDM-VQ-4 (200 DDIM steps, eta=0)5.11 (5.11)3.290.720.49https://ommer-lab.com/files/latent-diffusion/celeba.zip
FFHQUnconditional Image SynthesisLDM-VQ-4 (200 DDIM steps, eta=1)4.98 (4.98)4.50 (4.50)0.730.50https://ommer-lab.com/files/latent-diffusion/ffhq.zip
LSUN-ChurchesUnconditional Image SynthesisLDM-KL-8 (400 DDIM steps, eta=0)4.02 (4.02)2.720.640.52https://ommer-lab.com/files/latent-diffusion/lsun_churches.zip
LSUN-BedroomsUnconditional Image SynthesisLDM-VQ-4 (200 DDIM steps, eta=1)2.95 (3.0)2.22 (2.23)0.660.48https://ommer-lab.com/files/latent-diffusion/lsun_bedrooms.zip
ImageNetClass-conditional Image SynthesisLDM-VQ-8 (200 DDIM steps, eta=1)7.77(7.76)* /15.82**201.56(209.52)* /78.82**0.84* / 0.65**0.35* / 0.63**https://ommer-lab.com/files/latent-diffusion/cin.zip*: w/ guiding, classifier_scale 10 **: w/o guiding, scores in bracket calculated with script provided by ADM
Conceptual CaptionsText-conditional Image SynthesisLDM-VQ-f4 (100 DDIM steps, eta=0)16.7913.89N/AN/Ahttps://ommer-lab.com/files/latent-diffusion/text2img.zipfinetuned from LAION
OpenImagesSuper-resolutionLDM-VQ-4N/AN/AN/AN/Ahttps://ommer-lab.com/files/latent-diffusion/sr_bsr.zipBSR image degradation
OpenImagesLayout-to-Image SynthesisLDM-VQ-4 (200 DDIM steps, eta=0)32.0215.92N/AN/Ahttps://ommer-lab.com/files/latent-diffusion/layout2img_model.zip
LandscapesSemantic Image SynthesisLDM-VQ-4N/AN/AN/AN/Ahttps://ommer-lab.com/files/latent-diffusion/semantic_synthesis256.zip
LandscapesSemantic Image SynthesisLDM-VQ-4N/AN/AN/AN/Ahttps://ommer-lab.com/files/latent-diffusion/semantic_synthesis.zipfinetuned on resolution 512x512

Get the models

The LDMs listed above can jointly be downloaded and extracted via

bash scripts/download_models.sh

The models can then be found in models/ldm/<model_spec>.

Coming Soon...

Comments

BibTeX

@misc{rombach2021highresolution,
      title={High-Resolution Image Synthesis with Latent Diffusion Models}, 
      author={Robin Rombach and Andreas Blattmann and Dominik Lorenz and Patrick Esser and Björn Ommer},
      year={2021},
      eprint={2112.10752},
      archivePrefix={arXiv},
      primaryClass={cs.CV}
}

@misc{https://doi.org/10.48550/arxiv.2204.11824,
  doi = {10.48550/ARXIV.2204.11824},
  url = {https://arxiv.org/abs/2204.11824},
  author = {Blattmann, Andreas and Rombach, Robin and Oktay, Kaan and Ommer, Björn},
  keywords = {Computer Vision and Pattern Recognition (cs.CV), FOS: Computer and information sciences, FOS: Computer and information sciences},
  title = {Retrieval-Augmented Diffusion Models},
  publisher = {arXiv},
  year = {2022},  
  copyright = {arXiv.org perpetual, non-exclusive license}
}