V-Ray Tip: Reflection Catcher Workflow for Photoreal Plate Integration

Reflection catchers let you embed CG into photography by capturing believable reflections on matte geometry, so your renders sit naturally on real surfaces.

When to use:

• Product shots on glossy tables or floors.
• Archviz exteriors with wet asphalt or lobby stone.
• VFX set extensions where plates contain reflective cues.

Core setup (all hosts):

• Create a plane or surface that matches the reflective area in your backplate (shape and scale matter).
• Assign a V-Ray Wrapper/VRayMtlWrapper with:
  • Matte enabled.
  • Affect alpha on, Alpha contribution = -1 (full matte).
  • Reflection/Refraction catcher enabled (or “Matte for refl./refr.” in some hosts).
  • Shadows optional: on if you also need a shadow catcher; off for pure reflections.
• Use a VRayMtl as the base inside the wrapper to control the reflection look:
  • Reflection color/IOR to match the surface (e.g., IOR ≈ 1.52 for glassy stone, lower for coated floors).
  • Roughness for blur and spread; match micro-scratches with a roughness map if the plate suggests it.
• Load the backplate in the VFB background or environment override. Match camera FOV, horizon, and perspective first.
• Keep the catcher invisible but reflective:
  • Primary visibility off (or rely on Matte + Alpha contribution = -1).
  • Visible in reflections/refractions on.
  • Receive GI typically on; Generate GI off for stable integration.

Render elements and comp:

• Add Reflection, Refraction, Cryptomatte/Material ID for precise grading and isolation.
• Output 32‑bit EXR (premultiplied). The matte plane should cut cleanly in alpha while retaining reflection energy.
• In comp, place CG over the plate; use the Reflection element additively to boost or tame catch intensity.

Quality and performance tips:

• Use Clamp output or Max Ray Intensity to control fireflies from bright HDR highlights.
• Adaptive Dome + high-quality HDRIs minimize noise in glossy reflections.
• Lower Reflection Max Depth if you see unrealistic multiple bounces on the catcher.
• Leverage the V-Ray Denoiser on reflection-heavy AOVs for cleaner results at lower samples.

Host-specific notes:

• 3ds Max: VRayMtlWrapper + Object Properties for visibility flags.
• Maya: VRayMtlWrapper and vrayObjectProperties for matte/visibility toggles.
• SketchUp/Rhino: Wrapper Material has explicit “Reflection catcher” toggle alongside “Shadow catcher.”
• GPU: Modern V-Ray GPU supports matte/reflection catcher; confirm in your version’s notes.

Troubleshooting:

• Double images or “floating” reflections: check plane alignment and camera match; adjust roughness to match plate blur.
• Missing alpha cutout: ensure Affect alpha is on and Alpha contribution is -1.
• Too dark/light reflections: calibrate plate exposure in VFB Color Corrections or match with Film ISO/Shutter first.

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