img2img and Inpainting

Key Insight

img2img and inpainting show that the same trained diffusion model does far more than generate from scratch — both fall out of the Stable Diffusion sampling loop almost for free. The key control is the noise strength (also called denoising strength): instead of starting from pure noise, you partially noise an existing image and denoise from there, so a low strength keeps the original almost intact while a high strength redraws it freely. Inpainting adds a mask so only the selected region is regenerated while the known pixels are pasted back on every step — exactly how you erase an object or swap a face without disturbing the rest of the picture.