Diffusion models are a class of generative models that create data by learning to reverse a gradual noising process, transforming random noise into structured outputs through iterative denoising. Operating on the principle of stochastic differential equations and score-based modeling, they have achieved state-of-the-art results in image, video, and audio generation. Unlike GANs which require adversarial training or VAEs which compress data into fixed latent spaces, diffusion models iteratively refine noise using learned score functions, enabling highly controllable generation with stable training dynamics. The key insight is that reversing a carefully designed forward diffusion process—which progressively adds noise—can be learned as a denoising task, allowing models to generate diverse, high-fidelity outputs by starting from pure noise and gradually removing it through multiple timesteps.
What This Cheat Sheet Covers
This topic spans 13 focused tables and 96 indexed concepts. Below is a complete table-by-table outline of this topic, spanning foundational concepts through advanced details.
Table 1: Forward Diffusion Process
| Concept | Example | Description |
|---|---|---|
x_t = \sqrt{\bar{\alpha}_t} x_0 + \sqrt{1-\bar{\alpha}_t} \epsilon | • Gradually adds Gaussian noise to data over T timesteps until reaching pure noise• defines the corruption trajectory that the model learns to reverse | |
Linear: \beta_t = 0.0001 \to 0.02Cosine: \bar{\alpha}_t = \cos^2(\frac{t/T + s}{1+s} \cdot \frac{\pi}{2}) | • Controls variance \beta_t of noise added at each step• linear increases uniformly, cosine slows noise near endpoints to preserve signal longer | |
\text{SNR}(t) = \frac{\bar{\alpha}_t}{1 - \bar{\alpha}_t} | • Ratio of signal variance to noise variance at timestep t• determines how much original structure remains versus noise corruption | |
Rescale schedule so \text{SNR}(T) = 0 | Ensures pure noise at final timestep by forcing noise variance to dominate completely, eliminating train-inference mismatch from residual signal |