#
ControlNet

ControlNet models are adapters trained on top of another pretrained model. It allows for a greater degree of control over image generation by conditioning the model with an additional input image. The input image can be a canny edge, depth map, human pose, and many more.

If you’re training on a GPU with limited vRAM, you should try enabling the `gradient_checkpointing`, `gradient_accumulation_steps`, and `mixed_precision` parameters in the training command. You can also reduce your memory footprint by using memory-efficient attention with xFormers. JAX/Flax training is also supported for efficient training on TPUs and GPUs, but it doesn’t support gradient checkpointing or xFormers. You should have a GPU with >30GB of memory if you want to train faster with Flax.

This guide will explore the train_controlnet.py training script to help you become familiar with it, and how you can adapt it for your own use-case.

Before running the script, make sure you install the library from source:

    git clone https://github.com/huggingface/diffusers
    cd diffusers
    pip install .

Then navigate to the example folder containing the training script and install the required dependencies for the script you’re using:

PyTorch
Flax

    cd examples/controlnet
    pip install -r requirements.txt

🤗 Accelerate is a library for helping you train on multiple GPUs/TPUs or with mixed-precision. It’ll automatically configure your training setup based on your hardware and environment. Take a look at the 🤗 Accelerate Quick tour to learn more.

Initialize an 🤗 Accelerate environment:

    accelerate config

To setup a default 🤗 Accelerate environment without choosing any configurations:

    accelerate config default

Or if your environment doesn’t support an interactive shell, like a notebook, you can use:

    from accelerate.utils import write_basic_config

    write_basic_config()

Lastly, if you want to train a model on your own dataset, take a look at the Create a dataset for training guide to learn how to create a dataset that works with the training script.

The following sections highlight parts of the training script that are important for understanding how to modify it, but it doesn’t cover every aspect of the script in detail. If you’re interested in learning more, feel free to read through the script and let us know if you have any questions or concerns.

##
Script parameters

The training script provides many parameters to help you customize your training run. All of the parameters and their descriptions are found in the `parse_args()` function. This function provides default values for each parameter, such as the training batch size and learning rate, but you can also set your own values in the training command if you’d like.

For example, to speedup training with mixed precision using the fp16 format, add the `--mixed_precision` parameter to the training command:

    accelerate launch train_controlnet.py \
      --mixed_precision="fp16"

Many of the basic and important parameters are described in the Text-to-image training guide, so this guide just focuses on the relevant parameters for ControlNet:

- `--max_train_samples`: the number of training samples; this can be lowered for faster training, but if you want to stream really large datasets, you’ll need to include this parameter and the `--streaming` parameter in your training command
- `--gradient_accumulation_steps`: number of update steps to accumulate before the backward pass; this allows you to train with a bigger batch size than your GPU memory can typically handle

###
Min-SNR weighting

The Min-SNR weighting strategy can help with training by rebalancing the loss to achieve faster convergence. The training script supports predicting `epsilon` (noise) or `v_prediction`, but Min-SNR is compatible with both prediction types. This weighting strategy is only supported by PyTorch and is unavailable in the Flax training script.

Add the `--snr_gamma` parameter and set it to the recommended value of 5.0:

    accelerate launch train_controlnet.py \
      --snr_gamma=5.0

##
Training script

As with the script parameters, a general walkthrough of the training script is provided in the Text-to-image training guide. Instead, this guide takes a look at the relevant parts of the ControlNet script.

The training script has a `make_train_dataset` function for preprocessing the dataset with image transforms and caption tokenization. You’ll see that in addition to the usual caption tokenization and image transforms, the script also includes transforms for the conditioning image.

If you’re streaming a dataset on a TPU, performance may be bottlenecked by the 🤗 Datasets library which is not optimized for images. To ensure maximum throughput, you’re encouraged to explore other dataset formats like WebDataset, TorchData, and TensorFlow Datasets.

    conditioning_image_transforms = transforms.Compose(
        [
            transforms.Resize(args.resolution, interpolation=transforms.InterpolationMode.BILINEAR),
            transforms.CenterCrop(args.resolution),
            transforms.ToTensor(),
        ]
    )

Within the `main()` function, you’ll find the code for loading the tokenizer, text encoder, scheduler and models. This is also where the ControlNet model is loaded either from existing weights or randomly initialized from a UNet:

    if args.controlnet_model_name_or_path:
        logger.info("Loading existing controlnet weights")
        controlnet = ControlNetModel.from_pretrained(args.controlnet_model_name_or_path)
    else:
        logger.info("Initializing controlnet weights from unet")
        controlnet = ControlNetModel.from_unet(unet)

The optimizer is set up to update the ControlNet parameters:

    params_to_optimize = controlnet.parameters()
    optimizer = optimizer_class(
        params_to_optimize,
        lr=args.learning_rate,
        betas=(args.adam_beta1, args.adam_beta2),
        weight_decay=args.adam_weight_decay,
        eps=args.adam_epsilon,
    )

Finally, in the training loop, the conditioning text embeddings and image are passed to the down and mid-blocks of the ControlNet model:

    encoder_hidden_states = text_encoder(batch["input_ids"])[0]
    controlnet_image = batch["conditioning_pixel_values"].to(dtype=weight_dtype)

    down_block_res_samples, mid_block_res_sample = controlnet(
        noisy_latents,
        timesteps,
        encoder_hidden_states=encoder_hidden_states,
        controlnet_cond=controlnet_image,
        return_dict=False,
    )

If you want to learn more about how the training loop works, check out the Understanding pipelines, models and schedulers tutorial which breaks down the basic pattern of the denoising process.

##
Launch the script

Now you’re ready to launch the training script! 🚀

This guide uses the fusing/fill50k dataset, but remember, you can create and use your own dataset if you want (see the Create a dataset for training guide).

Set the environment variable `MODEL_NAME` to a model id on the Hub or a path to a local model and `OUTPUT_DIR` to where you want to save the model.

Download the following images to condition your training with:

    wget https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/diffusers/controlnet_training/conditioning_image_1.png
    wget https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/diffusers/controlnet_training/conditioning_image_2.png

One more thing before you launch the script! Depending on the GPU you have, you may need to enable certain optimizations to train a ControlNet. The default configuration in this script requires ~38GB of vRAM. If you’re training on more than one GPU, add the `--multi_gpu` parameter to the `accelerate launch` command.

16GB
12GB
8GB

On a 16GB GPU, you can use bitsandbytes 8-bit optimizer and gradient checkpointing to optimize your training run. Install bitsandbytes:

    pip install bitsandbytes

Then, add the following parameter to your training command:

    accelerate launch train_controlnet.py \
      --gradient_checkpointing \
      --use_8bit_adam \

PyTorch
Flax

    export MODEL_DIR="runwayml/stable-diffusion-v1-5"
    export OUTPUT_DIR="path/to/save/model"

    accelerate launch train_controlnet.py \
     --pretrained_model_name_or_path=$MODEL_DIR \
     --output_dir=$OUTPUT_DIR \
     --dataset_name=fusing/fill50k \
     --resolution=512 \
     --learning_rate=1e-5 \
     --validation_image "./conditioning_image_1.png" "./conditioning_image_2.png" \
     --validation_prompt "red circle with blue background" "cyan circle with brown floral background" \
     --train_batch_size=1 \
     --gradient_accumulation_steps=4 \
     --push_to_hub

Once training is complete, you can use your newly trained model for inference!

    from diffusers import StableDiffusionControlNetPipeline, ControlNetModel
    from diffusers.utils import load_image
    import torch

    controlnet = ControlNetModel.from_pretrained("path/to/controlnet", torch_dtype=torch.float16)
    pipeline = StableDiffusionControlNetPipeline.from_pretrained(
        "path/to/base/model", controlnet=controlnet, torch_dtype=torch.float16
    ).to("cuda")

    control_image = load_image("./conditioning_image_1.png")
    prompt = "pale golden rod circle with old lace background"

    generator = torch.manual_seed(0)
    image = pipe(prompt, num_inference_steps=20, generator=generator, image=control_image).images[0]
    image.save("./output.png")

##
Stable Diffusion XL

Stable Diffusion XL (SDXL) is a powerful text-to-image model that generates high-resolution images, and it adds a second text-encoder to its architecture. Use the `train_controlnet_sdxl.py` script to train a ControlNet adapter for the SDXL model.

The SDXL training script is discussed in more detail in the SDXL training guide.

##
Next steps

Congratulations on training your own ControlNet! To learn more about how to use your new model, the following guides may be helpful:

- Learn how to use a ControlNet for inference on a variety of tasks.