Corona to V-Ray Migration: Material Conversion, Light Mapping, and Render Settings Translation

Corona to V-Ray Migration: Material Conversion, Light Mapping, and Render Settings Translation

I've migrated several studios from Corona Renderer to V-Ray (and a few from V-Ray to Corona). Both are Chaos products, so the migration is smoother than between unrelated renderers, but there are specific conversion steps that need attention. The most common migration scenario I handle is studios that need V-Ray for specific features like GPU rendering, V-Ray Cloud, or compatibility with pipeline tools.

Why Migrate from Corona to V-Ray?

Common reasons I see:

• GPU rendering: V-Ray GPU supports CUDA and RTX acceleration; Corona is CPU-only (though Corona GPU is in development)
• V-Ray Cloud / Chaos Cloud: Cloud rendering integration
• Pipeline compatibility: V-Ray is the standard at many large studios
• Specific features: V-Ray Fur, V-Ray Mesh Export, V-Ray Proxy with LOD
• Real-time integration: V-Ray has tighter integration with Unreal Engine via V-Ray for Unreal

Step 1: Scene Conversion with Chaos Tools

Chaos provides built-in conversion tools in 3ds Max:

1. Install both Corona and V-Ray on the same 3ds Max installation
2. Go to V-Ray menu → Scene Converter
3. Select the Corona to V-Ray preset
4. Check the conversion options:
   • Materials: Convert Corona Physical Material to VRayMtl
   • Lights: Convert Corona Lights to V-Ray Lights
   • Environment: Convert Corona Sky/Environment to V-Ray Sky/Environment
   • Camera: Convert Corona Camera to V-Ray Physical Camera
5. Click Convert

What converts correctly:

• Corona Physical Material → VRayMtl (base color, roughness, metalness, normal map)
• Corona Light (Area) → V-Ray Area light
• Corona Light (Dome) → V-Ray Dome Light
• Corona Sun → V-Ray Sun
• Corona Sky → V-Ray Sky

What needs manual adjustment:

• Corona SSS: Converts to VRayMtl with SSS, but parameters don't map 1:1 — adjust scatter radius and amount manually
• Corona Displacement: Converts to V-Ray Displacement modifier, but amount and edge length values need recalibration
• Corona Light Portals: Convert to V-Ray Light portals, but verify orientation and size
• Corona Material presets: Some Corona-specific material features (like the clearcoat layer) need manual recreation in VRayMtl

Step 2: Material Conversion Details

Corona Physical Material → VRayMtl

| Corona Parameter | V-Ray Parameter | Notes | |-----------------|----------------|-------| | Base Color | Diffuse | Direct mapping | | Roughness | Reflection Glossiness | Invert: V-Ray uses glossiness (1=smooth), Corona uses roughness (1=rough) | | Metalness | Metalness | Direct mapping (both use 0-1) | | IOR | IOR | Direct mapping | | Bump/Normal | Bump/Normal | Direct mapping | | SSS Amount | Refraction/Translucency | Manual adjustment needed | | Clearcoat | Coat layer (VRayMtl 7+) | Manual setup if using older V-Ray |

Critical: Roughness → Glossiness inversion: This is the most common conversion error. Corona Roughness 0.3 = V-Ray Glossiness 0.7. The scene converter handles this automatically, but if you manually recreate materials, you must invert the roughness map using a Color Correction node with Invert enabled.

Glass Materials

Corona glass converts to V-Ray glass with these adjustments:

1. Thin shell in Corona → enable Thin-walled in V-Ray's refraction settings
2. Absorption in Corona → Fog color and Fog multiplier in V-Ray
3. Frosted glass (roughness) → set Refraction glossiness in V-Ray (invert the roughness value)

SSS Materials

SSS requires the most manual adjustment:

1. In VRayMtl, enable Translucency → Volumetric SSS
2. Scatter color: Direct mapping from Corona
3. Scatter radius: Corona uses millimeters, V-Ray uses scene units — verify the scale
4. Amount: Start at 0.5 and adjust — Corona and V-Ray calculate SSS differently

Step 3: Light Conversion Details

Corona Dome Light → V-Ray Dome Light

• HDRI map: Direct transfer
• Multiplier: May need adjustment — V-Ray and Corona use different light intensity scales
• Resolution: Set V-Ray Dome Light Dome resolution to 1024 (matching Corona's default)

Corona Sun → V-Ray Sun

• Intensity: V-Ray Sun uses different intensity units — typically needs 2-5x higher multiplier
• Size multiplier: Direct mapping (controls shadow softness)
• Turbidity: Direct mapping

Light Portals

• Corona Portal → V-Ray Light with Portal type enabled
• Verify the portal is facing the correct direction (into the room)
• V-Ray portals work with the V-Ray Dome Light — ensure the Dome Light is present

Step 4: GI Settings Translation

Corona and V-Ray use different GI systems:

| Corona Setting | V-Ray Equivalent | Notes | |---------------|-----------------|-------| | UHD Cache | Light Cache | Similar concept — precomputed GI cache | | Path Tracing (primary) | Brute Force (primary) | Direct mapping | | Force Path Tracing | Brute Force for both primary and secondary | Disable Light Cache | | Adaptive Light Solver | V-Ray Light Eval | Different algorithms, similar purpose |

My V-Ray GI setup for migrated scenes:

1. Primary GI: Brute Force
2. Secondary GI: Light Cache
3. Light Cache subdivs: 2000-4000 (equivalent to UHD Cache precision)
4. Light Cache sample size: 0.02 (default)
5. Brute Force subdivs: 16-32 (equivalent to Corona's GI vs AA balance)

Step 5: Render Settings Translation

| Corona Setting | V-Ray Equivalent | Notes | |---------------|-----------------|-------| | Noise Limit | Noise threshold | V-Ray uses 0.001-0.01; Corona uses 1-5% | | Max passes | Max subdivs | V-Ray uses total subdivs, not passes | | Denoiser | V-Ray Denoiser | Both support NVIDIA AI and Intel AI | | MSI | Max ray intensity | Similar concept — clamps bright samples |

Noise limit conversion: Corona Noise Limit 3% ≈ V-Ray Noise threshold 0.005. This is an approximation — you'll need to fine-tune based on visual results.

Denoiser: Both Corona and V-Ray support the NVIDIA GPU AI Denoiser and Intel AI Denoiser. The denoiser settings (amount, radius) translate directly.

Step 6: Camera and Exposure

Corona Camera → V-Ray Physical Camera:

• Exposure (EV): Direct mapping
• ISO: Direct mapping
• Shutter speed: Direct mapping
• Aperture (f-stop): Direct mapping
• White balance: Direct mapping (both use Kelvin temperature)

If the scene uses 3ds Max's standard camera (not a Corona Camera), no camera conversion is needed — V-Ray works with standard cameras.

Step 7: Post-Conversion Verification

After running the scene converter:

1. Render at low quality: Set V-Ray to low quality settings and render — check for obvious issues (black materials, missing lights, wrong colors)
2. Compare side-by-side: Render the same view in Corona (before conversion) and V-Ray (after conversion) — compare lighting, materials, and overall appearance
3. Check glass and SSS: These are the most likely to need manual adjustment
4. Verify light portals: Ensure portals are correctly positioned and oriented
5. Check displacement: Compare displacement results — V-Ray and Corona use different displacement algorithms

Common Migration Issues

Issue: Scene is much darker in V-Ray Fix: V-Ray and Corona use different light intensity scales. Increase light multipliers by 2-5x, or adjust the camera exposure.

Issue: Materials look different (roughness inverted) Fix: The scene converter should handle the roughness-to-glossiness inversion, but if materials look wrong, manually check the VRayMtl reflection glossiness values.

Issue: SSS looks melted or wrong Fix: SSS parameters don't convert 1:1. Manually adjust the scatter radius and amount in VRayMtl's translucency settings.

Issue: Render times are very different Fix: V-Ray and Corona optimize differently. V-Ray with Light Cache may be faster for interiors, while Corona's UHD Cache may be faster for exteriors. Adjust GI settings based on scene type.

Summary

Corona to V-Ray migration uses the built-in Scene Converter for automatic conversion, followed by manual adjustment of SSS, displacement, and light intensities. My migration process: run Scene Converter with Corona to V-Ray preset → verify materials (especially roughness-to-glossiness inversion) → adjust SSS parameters manually → verify light portal orientation → tune GI settings (Brute Force + Light Cache) → compare renders side-by-side → adjust light intensities for V-Ray's scale. The automatic converter handles 80-90% of the work; the remaining 10-20% is manual SSS, displacement, and light intensity calibration.