V-Ray Tip: Separate Refraction and AO for Art-Directable Compositing

Separating Refraction and Ambient Occlusion (AO) into dedicated render elements gives you precise, art-directable control in compositing with minimal re-rendering.

Why separate these passes:

• Targeted grading of glass, liquids, and plastics without touching the rest of the beauty.
• Flexible AO control to reinforce contact shadows only where needed.
• Cleaner look-development and faster client turnarounds by avoiding full re-renders.

Core setup:

• Add render elements:
  • Refraction (beauty contribution)
  • Raw Refraction and Refraction Filter (for energy-correct compositing: Raw × Filter)
  • VRayExtraTex with a VRayDirt map for AO
• Material settings for refractive objects (glass, liquids):
  • Enable Refraction (IOR > 1.0) and proper Affect channels = Color+alpha or All channels so AOVs and alpha are accurate.
  • Use realistic IOR (e.g., glass ≈ 1.52) and sensible Refraction Depth to capture multi-bounce transmission without oversampling.
• AO (VRayDirt) suggestions:
  • Radius in real-world units matching scene scale (try 2–10 cm for product; 10–50 cm for archviz, then refine).
  • Enable “Ignore self-occluded back faces” to avoid darkening thin shells.
  • Use “Work with transparency” if you rely on cutouts/opacity maps.
  • Plug VRayDirt into VRayExtraTex, color = white for unoccluded and dark gray/black for occluded; keep it linear.
• Denoising:
  • Add VRayDenoiser and, if needed, enable Denoise Render Elements; often leave AO un-denoised for crisp contact edges.
• Output:
  • Save as 32‑bit multi-channel EXR (linear). View in sRGB; grade in linear or ACES as your pipeline dictates.
  • Name elements consistently (e.g., “refraction”, “raw_refraction”, “refract_filter”, “ao_extraTex”).

Compositing guidelines:

• Refraction: Reconstruct as Raw Refraction × Refraction Filter, then grade/tint the product. Merge back with the beauty using the renderer’s standard comp tree or an Add/Plus where appropriate.
• AO: Multiply over Diffuse/Albedo or GI only (not over full beauty) to avoid double-darkening. Keep AO subtle (5–20% opacity).
• Use Cryptomatte or Object/Material IDs to isolate specific glass assets for localized tweaks.

Quality and performance tips:

• Use consistent anti-aliasing for beauty and elements (same sampler/noise threshold) for clean recomposition.
• Clamp excessively bright HDR highlights with Max Ray Intensity to reduce fireflies in glass.
• If many refractive bounces are unnecessary, reduce Refraction Depth to cut render time.
• For interiors with HDRI, pair with Adaptive Lights and good dome sampling to tame noise in transmission.

Workflow boosters:

• Iterate with IPR and VFB Regions, then commit finals in Bucket mode.
• Use Render History to A/B refraction tints and AO radii quickly.

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