From Diffusion Models to All Generative Networks: The Power of ControlNet
Tags: ai, machinelearning, datascience, opensource
Published: 2023-03-11 22:16:00

## Introduction

Neural networks have become increasingly popular in recent years due to their ability to learn complex patterns from data. However, designing and training neural networks can be a challenging task, especially when it comes to controlling their behavior. Fortunately, a new architecture called ControlNet has been developed to help control the overall behavior of neural networks. In this blog post, we'll discuss what ControlNet is, how it works, and its potential to be used in other generative models.


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## What is ControlNet?

ControlNet is an architecture that involves connecting two copies of any network, one locked and one free for training. The locked copy preserves the original capabilities of the network, while the trainable copy manipulates the inputs conditions of neural network blocks to control the overall behavior of the network. The two networks are connected with zero convolutions, and the convolution weight and bias are initialized at zero, referred to as zero convolutions or 1x1 convolution.

During the training phase, the locked copy preserves the original capabilities of the network, while the trainable copy manipulates the inputs conditions of neural network blocks. If the input of the trainable copy condition is non-zero, the network's gradients are calculated correctly. This ensures that the weights of the convolution increase from zero to successfully control the locked network.

## How Does ControlNet Work?

The architecture of ControlNet involves having two copies of the network: one locked and one free for training. The locked copy preserves the original capabilities of the network, while the free copy can be trained and has the capability of modifying the output of the original. The two networks are connected with zero convolutions.


![Control net general](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/6uhlzd5pz0py3tcg1qh9.png)

ControlNet manipulates the inputs conditions of neural network blocks so as to further control the overall behavior of an entire neural network. During the initial training steps, the copy control net network does not modify anything in the output of the original. This approach ensures good results right from the beginning of the training. If the results are poor, this may indicate that the training has failed.

## ControlNet and Stable Diffusion

When training stable diffusion control net, a small network is employed to capture the latent features of the images with the same convolution shapes. Note that this small network is trained alongside the main, trainable network. As shown in the figure, when using ControlNet with diffusion models, only the encoder blocks are duplicated. With this architecture, we can use ControlNet with almost all stable diffusion versions.


![Diffusion control net](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/3kiph3n0non2iw3xco61.png)

There are a couple of methods to speed up the training process. One is to initially connect only the middle block of the diffusion model. This will speed up the training time. Once reasonable results are achieved, the rest of the decoder layers can be connected. In practice, we can use one of the pre-trained ControlNet networks and fine-tune it for a specific control that we need.

## Advantages of ControlNet

The main advantage of ControlNet is that it provides a way to control the behavior of neural networks, which can be extremely useful in a variety of applications, such as image and speech recognition, natural language processing, and autonomous vehicles. By manipulating the inputs conditions of neural network blocks, we can specify the requirements of the network, which can result in more accurate and efficient models.

Another advantage of ControlNet is that it can be used on any model, not just diffusion models. This means that we can explore other potential uses for ControlNet and apply it to other generative models.

## Conclusion

ControlNet is an architecture that provides a way to control the input conditions of neural network blocks and control the overall behavior of the network. This architecture can be used to speed up the training process and specify the requirements of the network. ControlNet has the potential to be more than just a way of taming diffusion models; it could be a good general idea for controlling all generative networks. By exploring other potential uses for ControlNet and refining the architecture, we can expect to see it become a standard tool for machine learning practitioners.

What do you think about ControlNet? Do you see any potential limitations or drawbacks to this architecture? Let's discuss in the comments below!

Paper: https://arxiv.org/abs/2302.05543