V-Ray Tip: Separate Matte, Reflection, and Refraction Passes

Gain precise post-production control by splitting matte, reflection, and refraction into dedicated Render Elements. This approach lets you rebalance surfaces and glass without re-rendering.

Why separate these passes

• Isolate surfaces with clean mattes for targeted color and exposure tweaks.
• Independently grade reflections and refractions to tame hotspots or boost sparkle.
• Fix client notes on glass and metals in comp, not in re-renders.
• Deliver robust multi-pass EXRs that travel well through any pipeline.

Core elements to add

• Matte: Cryptomatte (preferred), plus optional Material ID / Object ID (or MultiMatte in 3ds Max).
• Reflection: Reflection, Raw Reflection, Reflection Filter.
• Refraction: Refraction, Raw Refraction, Refraction Filter.
• Optional for modern shaders: Specular (direct glossy), Coat (if using clearcoat), Emission (if any).

Quick setup by host

• V-Ray for 3ds Max: Render Setup > Render Elements > Add… (choose elements above).
• V-Ray for Maya: Render Settings > Render Elements > Add.
• V-Ray for SketchUp/Rhino: Asset Editor > Render Elements > Add.

Save as multi-layer EXR

• Use 32‑bit half/float OpenEXR with all passes embedded via the V-Ray Frame Buffer (Save All Channels).
• Keep a single EXR per frame for reliable relinking in comp and reviews.

Material settings that affect passes

• Glass alpha: In VRayMtl Refraction > Affect channels, pick “Color only” to keep a solid alpha (useful for CG-on-plate). Choose “Color+alpha” if you want cutout transparency through glass.
• Holdouts: Use VRayMtlWrapper or Object Properties to set Matte object, Alpha contribution = -1, and affect shadows for perfect CG/compositing integration.

Compositing recipe (linear workflow)

• Work in linear color; manage view transforms (OCIO/ACES) in your comp tool.
• If you use “Reflection” and “Refraction” elements: simply add (plus) them over your base diffuse/lighting result.
• If you prefer “Raw” workflow: - Reflection = Raw Reflection × Reflection Filter, then add. - Refraction = Raw Refraction × Refraction Filter, then add.
• Use Cryptomatte to pull artifact-free masks per object/material and grade selectively.
• For glass tweaks, adjust Refraction exposure/contrast separately from Reflection to control brightness without flattening highlights.

Pro tips and pitfalls

• Keep denoising consistent: either use denoised beauty plus denoised element set, or keep all raw for maximum flexibility.
• Avoid clamping during final renders to preserve highlight range in reflection/refraction.
• When metals look “double bright,” check you’re not stacking Specular and Reflection redundantly; follow your renderer’s element nomenclature.
• Batch-apply element presets across shots to maintain predictable comp builds.

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