V-Ray Tip: Precompute Irradiance Map and Light Cache for Stable Animation GI

For stable, flicker-free Global Illumination in animation, precompute an Irradiance Map and reuse it across frames.

When to use it

• Best for camera-only animations with static geometry and lighting.
• Ideal for interiors or complex diffuse lighting where Brute Force would be too slow.
• Avoid when objects, lights, or materials change significantly per frame—use Brute Force GI instead in those cases.

Core setup

• Primary GI: Irradiance Map (IR).
• Secondary GI: Light Cache (LC).
• Render engine: CPU. IR is a CPU method; on GPU, prefer Brute Force + Light Cache.

Light Cache preparation

• Enable Use camera path to sample the entire camera trajectory in one pass.
• Subdivs: 1500–2500 for 1080p interiors; scale up for 4K or very glossy scenes.
• Sample size: match scene scale; smaller values increase detail but add time. Keep Prefilter on for stability.
• Auto-save the LC to file; you will point the final render to this cache.

Irradiance Map settings (guidelines)

• Min/Max rate: interiors typically −3/−1 at 1080p; exteriors can use −4/−2. Increase one step for 4K or tight spaces.
• HSph. subdivs: 50–80; Interp. samples: 20–35 for smooth blending.
• Thresholds: Color ≈ 0.3, Normal ≈ 0.15–0.2, Distance ≈ 0.1 (adjust for scene scale).
• Disable Detail enhancement for animation to avoid temporal noise.

Two-phase workflow

• Phase 1 — Prepass:
  • IR Mode: Animation (prepass).
  • Resolution: you can compute at 50–75% of final resolution to save time.
  • Render every 5th–10th frame to build coverage (denser sampling on fast moves).
  • Enable Incremental add to current map (where available) and Auto-save to a shared path.
  • Keep motion blur and depth of field off during prepass.
• Phase 2 — Final rendering:
  • IR Mode: Animation (rendering) and load the saved IR file.
  • LC: From file (load the saved LC).
  • Re-enable DOF/MB if needed; these won’t affect the GI cache.

Quality and robustness tips

• Lock scene changes before caching. Any lighting/material change requires a new cache.
• For shots with moving doors/props, consider:
  • Switching Primary GI to Brute Force for those objects or the whole shot, or
  • Rendering two passes (static background with IR + comp moving elements lit with BF).
• Use a temporal denoiser for animation where available and keep Noise threshold conservative (e.g., 0.01–0.02).
• Monitor the V-Ray log and Sample Rate to spot undersampled regions; adjust IR rates or HSph subdivs as needed.

Pipeline notes

• Precompute once, render anywhere: store IR/LC caches on a network path accessible to all nodes.
• Version your caches per shot and camera to prevent mix-ups on the farm.

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