Compositing & Post-Processing

Module 4: Compositing & Post-Processing 

1. Multi-Pass Rendering (AOVs – Arbitrary Output Variables)

Multi-pass rendering breaks down a scene into individual components (AOVs) for precise control in compositing.

• Beauty Pass Breakdown

• Diffuse Pass: Raw surface color without shadows/specularity.

• Specular Pass: Reflections and glossy highlights.

• Shadow Pass: Isolated shadows for intensity adjustment.

• Emission Pass: Self-illuminating elements (neon signs, screens).

• Utility Passes: Z-depth (for fog/depth effects), Normals (relighting).

• Cryptomatte for Object Isolation

• Automated ID masking using metadata (no manual rotoscoping).

• Workflow: Renders generate per-object/ material masks for quick selections in Nuke/After Effects.

2. Advanced Post-Processing

Enhances renders with cinematic effects that mimic real-world cameras and lenses.

• Lens Effects

• Chromatic Aberration: RGB color splitting (simulates lens distortion).

• Use Case: Stylized looks or realism in VR/archviz.

• Vignette: Darkens edges to focus attention.

• Control: Shape (round/oval), falloff (hard/soft).

• Color Grading with LUTs (Look-Up Tables)

• 1D/3D LUTs: Apply pre-defined color transforms (e.g., film emulation).

• Example: Converting log footage to Rec.709 with ARRI LUTs.

• Custom LUTs: Created in DaVinci Resolve for consistent stylization.

3. Integration with Compositors

Professional workflows use node-based compositors for non-destructive editing.

• Nuke/Fusion Workflows

• Nuke (Industry Standard):

• Merge Operations: Over, screen, multiply for layer blending.

• 3D Compositing: Camera projections within comps.

• Fusion (Free Alternative):

• GPU-Accelerated: Faster for real-time previews.

• *VR/360° Support:* Spherical compositing tools.

• Deep Compositing

• Stores per-pixel depth data (not just RGBA).

• Use Cases:

• Volumetric elements (smoke/fire) with correct occlusion.

• Corrected depth-based blending in CG/live-action integration.

Key Takeaways:

• AOVs enable surgical adjustments (e.g., boosting specularity without affecting diffuse).

• Post-Processing adds "imperfections" for realism (lens effects) or mood (color grading).

• Compositing bridges rendering and final output (Nuke for films, Fusion for indie projects).