Stable Diffusion 3: Scaling Rectified Flow Transformers for High-Resolution Image Synthesis

Gabriel Mongaras
28 Mar 202462:29

TLDRStable Diffusion 3 is an impressive open-source model that excels at generating images from text prompts. It utilizes a combination of transformers, rectified flows, and latent space encoding to create detailed and accurate visual outputs. The model is trained on a mix of ImageNet and CC12M datasets, with recaptioned data to enhance training efficiency. It integrates both CLIP and T5 encoders to process text information, with T5 playing a crucial role in generating high-quality textual content. The model also employs sinusoidal embeddings to denote time steps and positional information within the diffusion process. Notably, Stable Diffusion 3 outperforms other solvers and demonstrates a strong correlation between human preference and validation loss, indicating its potential as a powerful tool in the realm of AI-generated imagery.


  • 🌟 Introduction of Stable Diffusion 3, an advanced open-source diffusion model with impressive capabilities.
  • πŸ“ˆ Utilization of Transformer architecture in the model, marking a shift from unit-based models to sequence-to-sequence approaches.
  • πŸ” The model's ability to handle text and images by encoding them into a latent space, allowing for cross-modality interactions.
  • 🎨 The use of rectified flows for the diffusion process, providing a novel approach to learning the ordinary differential equation (ODE) backward in time.
  • πŸ”— Integration of CLIP and T5 models for text encoding, which helps the model understand and generate text with visual knowledge.
  • πŸ–ΌοΈ The model operates in the latent space, using autoencoders or variational autoencoders to transform images into a computationally friendly format.
  • πŸ“š Training on large datasets like ImageNet and CC12M, with recaptioning to improve data quality and model performance.
  • 🌐 Multiple encoders for text and latent information, with the model learning from both high-level and fine-grained details.
  • πŸ”„ The model's ability to refine its output through multiple steps, correcting any errors and improving the final image generation.
  • πŸ“Š Human preference for the generated images is highly correlated with validation loss, indicating the model's effectiveness.
  • πŸš€ Potential for future improvements and applications, with the model showing better performance than previous versions and other solvers.

Q & A

  • What is the main feature of Stable Diffusion 3?

    -Stable Diffusion 3 is an advanced open-source diffusion model that introduces a new capability for spelling, which was not possible with previous versions. It also represents a significant step forward for Transformer-based models in the field of diffusion.

  • How does the diffusion model work in the context of the script?

    -The diffusion model works by gradually adding noise to an image over a series of time steps until it reaches a state of pure Gaussian noise. The model is then trained to reverse this process, learning to predict and remove the noise from an image to recover the original signal.

  • What is the role of the Transformer in the diffusion model?

    -In the diffusion model, the Transformer plays a crucial role in learning the sequence-to-sequence relationship between the noisy image and the original image. It is trained to predict the noise in the image at each time step, which can then be subtracted to retrieve the original image.

  • How does the script explain the training process of the diffusion model?

    -The script explains that the diffusion model is trained using a noise-matching objective, where the model learns to predict the noise in the image at various time steps. The training process involves minimizing the mean squared error between the predicted noise and the actual noise in the image.

  • What is the significance of the rectified flows in Stable Diffusion 3?

    -Rectified flows are used in Stable Diffusion 3 to model the ordinary differential equation (ODE) that describes the diffusion process. They allow the model to learn a trajectory from the data distribution to the noise distribution, which is essential for the reverse process of recovering the original image from the noise.

  • How does the script discuss the use of the score function in diffusion models?

    -The script mentions the score function as a way to maximize the probability of the image existing, using steepest ascent. The score is essentially the gradient of the probability with respect to the input image, and by maximizing this score, the model can generate high-quality images.

  • What is the role of the variational autoencoder in the diffusion model?

    -The variational autoencoder is used to encode the image into a latent space, which is a more computationally friendly representation. The diffusion process is then applied to this latent space, and after the noise is removed, the image is decoded back to its original form.

  • How does the script address the training of the autoencoder and diffusion model?

    -The script explains that the autoencoder and diffusion model are trained independently. The autoencoder is trained on a large dataset of images to compress them into a latent space, and then the diffusion model is trained in this latent space to reverse the noise addition process.

  • What is the significance of the time step in the diffusion process?

    -The time step is crucial in the diffusion process as it represents the progression from the original signal to the noise. The model uses sinusoidal embeddings to uniquely represent each time step, which helps guide the reverse process of removing noise and recovering the original image.

  • How does the script describe the use of conditional information in the diffusion model?

    -The script describes the use of conditional information, such as text captions and time steps, to modulate the distribution of pixel values in the image. This allows the model to generate images that are not only aesthetically pleasing but also adhere closely to the provided prompts or captions.



πŸš€ Introduction to Stable Diffusion 3

The paragraph introduces Stable Diffusion 3, highlighting its positive reception based on demos and early access reviews. It mentions new capabilities of the model, such as spelling, which was not possible in previous versions. The speaker expresses hope for the model's longevity and stability, and suggests that it will be a significant step for open-source diffusion models. The theory behind the model is also mentioned as being interesting, and the speaker anticipates discussing how diffusion models work in more detail.


πŸ“ˆ Understanding the Forward and Backward Process

This paragraph delves into the forward and backward processes of diffusion models. The forward process involves adding noise to an image to create a noisy version, while the backward process is about training a model to reverse this by predicting the noise in the image. The speaker explains the training of a model, denoted as m_Theta, to refine the prediction over multiple steps, using an iterative approach to gradually remove noise and recover the original image. The concept of noise matching objective and the use of a deterministic process are also discussed.


πŸ”„ The Role of ODEs, SDEs, and Refinements in DDPM

The speaker discusses the evolution of diffusion models, starting with DDPM and moving towards the use of ODEs and SDEs. The paragraph explains how score-based models and the concept of a noise distribution guided by a stochastic process are used to transition from the data distribution to a noise distribution. The idea of using an SDE to model the forward process and an ODE for the backward process is introduced, with a focus on the refinement procedure that improves the model's predictions over multiple steps.


πŸŒ€ Multiple Steps and Trajectory Modeling in Diffusion Models

This paragraph emphasizes the importance of multiple steps in the diffusion process due to the curved trajectory in high-dimensional space. The speaker explains that a single step is not sufficient for accurate predictions, and multiple iterations are needed to correct the model's trajectory. The concept of modeling the data as a velocity function and using rectified flows to learn the backward process in time is introduced, along with the objective of velocity matching and its transformation into a noise-matching objective.


🎨 Encoding Images and Text for Stable Diffusion 3

The paragraph discusses the encoding process for both images and text in Stable Diffusion 3. It explains the use of a variational autoencoder to transform images into a latent space and the process of encoding text using models like CLIP and T5. The speaker details how images are broken down into patches and flattened, and how text is encoded with fine-grained and lightweight information. The combination of text and image information, along with time step embeddings, is described as a crucial part of the model's architecture.


πŸ”§ Model Training and Conditional Modulation

This section covers the training aspects of the Stable Diffusion 3 model, including the use of recaptioned datasets like ImageNet and CC12M for better annotations. The importance of pre-training on low-resolution images before fine-tuning on higher resolutions is highlighted. The role of normalization and the introduction of RMS norm to stabilize attention entropy during half-precision training are also discussed. The paragraph concludes with the model's performance comparison with other solvers and the impact of adding a third modality.



πŸ’‘Stable Diffusion 3

Stable Diffusion 3 is a new iteration of a generative model that is capable of producing high-quality images. It is an open-source model that has gained attention for its ability to synthesize complex visual data. In the context of the video, Stable Diffusion 3 is presented as a significant advancement in the field of AI and image generation, showcasing impressive sample outputs and new capabilities that were not possible with previous versions.


A Transformer is a type of deep learning model that is particularly effective for handling sequential data, such as text or time series. It relies on self-attention mechanisms to weigh the importance of different inputs at different positions. In the video, the Transformer is used as a core component of the Stable Diffusion 3 model, indicating its role in processing and generating complex data sequences, such as the steps involved in the diffusion process.

πŸ’‘Diffusion Model

A diffusion model is a class of generative models that simulate the process of gradually reversing the effect of noise applied to data, such as images. These models learn to recover the original data by training on a sequence of progressively less noisy versions of the data. In the context of the video, the diffusion model is central to the Stable Diffusion 3's functionality, as it describes the process of turning noise back into meaningful images.

πŸ’‘Early Access

Early Access refers to a software release strategy where a product is made available to a limited group of users before its official release. This allows for testing, feedback, and improvements to be incorporated before a wider launch. In the video, the mention of Early Access implies that some users have already gained access to Stable Diffusion 3 and are providing feedback on its performance, contributing to its ongoing development.

πŸ’‘Latent Space

Latent space is a term used in machine learning to describe an abstract space where the underlying, often unobserved, variables that determine the surface variables are located. In the context of the video, the latent space refers to the transformed version of the image data that the diffusion model operates on, which is a lower-dimensional, compressed representation of the original data.

πŸ’‘Variational Autoencoder (VAE)

A Variational Autoencoder (VAE) is a type of generative model that uses an encoder to map input data into a latent space and a decoder to map the latent space back into the original data space. VAEs are particularly useful for creating new data points that resemble the input data. In the video, VAEs are used to encode images into a latent space where the diffusion process takes place, and then to decode the processed latent data back into images.

πŸ’‘Noise Matching Objective

The noise matching objective is a training goal in diffusion models where the model learns to predict the noise that has been added to the data. By accurately predicting and removing this noise, the model can reverse the diffusion process and recover the original, undisturbed data. In the context of the video, this objective is crucial for training the Stable Diffusion 3 model to generate high-quality images.

πŸ’‘Rectified Flows

Rectified flows are a mathematical concept used in the context of the video to describe a specific type of normalization flow used in the training of the diffusion model. They are part of the process that allows the model to learn the optimal trajectory for reversing the noise addition process. The use of rectified flows is a technical aspect that contributes to the model's ability to efficiently and effectively generate images.

πŸ’‘Prompt Adherence

Prompt adherence refers to the ability of a generative model to follow the instructions or constraints provided in a prompt, such as creating an image that matches a given description. In the context of the video, prompt adherence is an important metric for evaluating the performance of the Stable Diffusion 3 model, as it indicates how well the model can generate images that align with the textual descriptions provided as inputs.

πŸ’‘Human Preferences

Human preferences refer to the subjective opinions and tastes of individuals when evaluating the quality or appeal of something, such as images generated by a model. In the context of the video, human preferences are used as a benchmark to compare the aesthetic quality of images produced by the Stable Diffusion 3 model, indicating a high level of correlation with validation loss and serving as an important metric for model evaluation.


Stable Diffusion 3 is released, showcasing impressive advancements in the open-source diffusion model domain.

The model introduces a new capability for Stable Diffusion, which is the ability to spell, a feature not present in previous versions.

Stable Diffusion 3 demonstrates a significant improvement over its predecessors, particularly in the area of latent and diffusion models.

The model uses a Transformer architecture, which is a departure from the traditional unit model used in previous diffusion models.

Attention mechanism plays a crucial role in the model, with the ability to refine and improve predictions through a chain of iterative processes.

The model employs a diffusion process that transitions from the original signal to pure noise, and then reverses this process to recover the original image.

A key innovation in Stable Diffusion 3 is the use of rectified flows, which allows for a more accurate and efficient learning of the reverse diffusion process.

The model operates in the latent space rather than pixel space, leveraging the computational efficiency and representational power of latent features.

Stable Diffusion 3 utilizes a variational autoencoder to encode and decode images in the latent space, which is separate from the diffusion model training.

The paper discusses the use of CLIP and T5 models for encoding text information, which is then integrated with the image diffusion process.

The model is trained on a mix of ImageNet and COCO 12M datasets, with recaptioning performed to improve the quality of the training data.

The addition of the third modality did not significantly improve the model's performance, indicating that the combination of text and image flows is optimal.

Human preference for the generated images is highly correlated with the validation loss, indicating the model's effectiveness in producing aesthetically pleasing content.

The model was pre-trained on low-resolution images and then fine-tuned on higher resolutions, demonstrating the flexibility and scalability of the approach.

A novel normalization technique involving the RMS norm was introduced to stabilize attention entropy during training, especially in half-precision environments.

The use of sinusoidal embeddings for time steps is highlighted as a unique method for providing the model with a sense of progression during the diffusion process.

The paper emphasizes the importance of T5 in generating high-quality textual descriptions and its significant contribution to the model's capabilities.

Rectified flows in Stable Diffusion 3 are shown to outperform other solvers, demonstrating the model's effectiveness in comparison to existing technologies.