Inner Frustum

Understanding Inner Frustum

In virtual production, the LED volume serves two distinct purposes: providing the background image captured on camera (inner frustum) and providing environmental lighting and reflections (outer frustum). The inner frustum is the critical zone that becomes part of the final footage.

Frustum Geometry

**Definition:** The frustum is the pyramid-shaped volume visible through the camera lens. When this pyramid intersects the LED wall, it creates the inner frustum zone.

**Determining Factors:**

• Camera position in space
• Lens focal length
• Sensor size and aspect ratio
• Focus distance (for depth of field)

Technical Requirements

**Resolution:** Inner frustum content must exceed the camera's capture resolution when projected onto the LED surface. 4K minimum, often 8K+ for large volumes.

**Perspective:** Content renders from the exact virtual camera position matching the physical camera, creating accurate depth and parallax.

**Update Rate:** The frustum boundaries and content update every frame as the camera moves, requiring real-time calculation.

Rendering Priority

**Quality Zones:** Virtual production systems allocate rendering resources by priority:

1. **Inner Frustum**: Full resolution, all effects 2. **Frustum Edge**: Transition zone 3. **Outer Frustum**: Reduced quality, lighting focus

**Performance Optimization:** Limiting full-quality rendering to the visible area allows larger virtual environments without overwhelming GPU resources.

Camera Tracking Integration

**Position Data:** Tracking systems report camera position to the render engine, which calculates:

• Frustum boundaries on LED surface
• Virtual camera position in scene
• Correct perspective for rendering

**Latency Requirements:** The entire chain—tracking, calculation, rendering, display—must complete within one frame to maintain synchronization.

Visual Considerations

**Frustum Edge:** The boundary between inner and outer frustum must be carefully managed:

• Soft transitions prevent visible edge
• Color matching between zones
• Resolution blending

**Screen Size:** Larger inner frustums require:

• Wider LED coverage
• Higher content resolution
• More rendering power

Operational Workflow

**Pre-Production:**

• Plan shot compositions
• Calculate frustum requirements
• Verify LED coverage adequate

**On Set:**

• Monitor frustum display
• Verify tracking accuracy
• Adjust boundaries as needed