🎯Core Definition
The three major generation families trade off quality/diversity/speed. GANs play a zero-sum game between generator and discriminator — one forward pass is fastest, but adversarial training is unstable and prone to mode collapse. Diffusion/flow models generate by progressive denoising: training is stable regression and diversity is strong, and current SOTA FID is lower (higher quality ceiling). Autoregressive models predict token by token — great for text and discrete modalities with natural conditioning, but sampling is serial. Comparison:
📌Overview
| Dimension | GAN | Diffusion (DDPM/distilled) | Autoregressive |
|---|---|---|---|
| Training stability | poor (adversarial) | good (MSE regression) | good (cross-entropy) |
| Diversity | poor (mode collapse) | good (full coverage) | good |
| Quality (FID) | realistic in-mode | SOTA lowest FID | weaker on images |
| Sampling speed | 1 step (fastest) | 4–1000 steps (DDIM/distillable) | serial tokens |
| High-res scaling | unstable | latent + DiT scalable | hard |
📌Overview
FID (Fréchet Inception Distance): pass real and generated images through an Inception network, assume the features are Gaussian, and measure the Fréchet distance between their means and covariances:
📌Overview
FID=∥μr−μg∥2+Tr(Σr+Σg−2(ΣrΣg)1/2) 📌Overview
Lower is better; it captures both fidelity and diversity, though note they are not the same — a GAN can have decent FID yet poor diversity.
💡Use Cases
interview comparison questions (“why is text-to-image SOTA diffusion, not GAN?”); architecture selection — low-latency interactive tasks (real-time filters, SR) favor GANs or distilled diffusion, quality/diversity-first tasks (text-to-image, video) favor diffusion.
⚡Key Problems Solved
GANs' unstable adversarial training, mode collapse and hard high-resolution scaling; diffusion trades more sampling steps for stable training, full distribution coverage and lower FID; autoregressive models have been largely displaced for image generation by diffusion/flow models.