Render Region (Ctrl+B)

Don’t render the whole frame.

The Workflow

1. Press Ctrl + B in the viewport.
2. Drag a box around a specific area (e.g., the character’s face).

The Technique

Cycles will only render inside that red box. This allows for lightning-fast iteration on specific details without wasting GPU power on the background. To clear the region and render everything again, press Ctrl + Alt + B.