Negative Prompts and How They Work Mechanically

1Key Takeaways

• There is no negative-prompt mechanism in a diffusion model.
• There is a text field that gets encoded and put where the empty string normally goes — in the unconditional branch of classifier-free guidance — and every property of negative prompts, including the surprising ones, falls out of that one substitution.
• The short answer Guidance evaluates the denoiser twice per step: once with your prompt, once with an empty prompt.
• The two predictions are combined by extrapolating away from the….