Outer Frustum

Overview

The Outer Frustum (German roughly "outer cone of vision") is a term from Virtual Production and the In-Camera VFX (ICVFX) workflow on LED volumes. It refers to the entire area of the LED wall that lies outside the current camera field of view – in other words, everything that the production camera is not currently capturing directly.

Its counterpart is the Inner Frustum: the camera-tracked, perspective-correct window on the LED wall, rendered in full "final pixel" quality, which the camera actually captures as the background. The Outer Frustum, on the other hand, is not needed for direct capture but serves an lighting function.

Function on Set

The Outer Frustum is essentially a lighting and reflection tool. From the perspective of the lighting department, the LED wall outside the camera's image acts as a huge, colorfully controllable light source:

• Interactive Light (Spill): The illuminated surfaces cast ambient light onto actors, costumes, and sets – matching the depicted scene (sunset, neon street, firelight).
• Reflections: In shiny surfaces like eyes, lacquer, glass, metal, or water, the environment of the Outer Frustum is realistically reflected – an effect that cannot be achieved with traditional greenscreen.
• Continuity: While the Inner Frustum follows the camera, the Outer Frustum remains consistent for the rest of the volume, thus ensuring uniform, believable illumination.

Technical Classification

The Outer Frustum is typically displayed at a lower resolution or lower render quality than the Inner Frustum. Since this area does not end up in the final image but "only" provides light and reflections, processing power can be saved here – this reduces latency and artifacts when panning, tilting, or zooming the camera.

The system of real-time engines (often Unreal Engine with nDisplay) is controlled via the so-called "Brain Bar," which coordinates camera tracking, Inner Frustum, and Outer Frustum on the LED panels. Important for understanding on set:

• The Inner Frustum follows the tracked camera in real-time.
• The Outer Frustum remains largely independent of this and serves as the lighting environment for the entire volume.
• If an object or reflection leaves the Inner Frustum, the lower-resolution Outer Frustum visually "takes over" – a transition that must be considered during set planning and framing.