Can I render a V-Ray model with Corona directly?

Not correctly. The V-Ray materials and maps are not evaluated by Corona. Convert them with the Corona Converter, or rebuild the materials, and then test with a render.

Which parts of a model are lost most often when converting?

Displacement, layered materials, special maps such as dirt or edges, IES light settings and proxies. Check these in a test render before you use the model in a project.

Is it better to convert or to rebuild the material?

For simple materials, rebuilding is quick and gives a cleaner result. For complex ones, convert first and fix what is off. If the result needs a lot of correction, rebuild it.

Corona or V-Ray: using models built for the other engine

Updated October 6, 20265 min read

What survives and what is lost when you convert a downloaded model between Corona and V-Ray: displacement, layered materials, IES lights, maps and a workflow that works.

Why a model for the other engine does not just work

Corona and V-Ray are both physically based renderers, but each one has its own materials, maps and light objects. A model prepared for V-Ray has VRayMtl materials and V-Ray maps. Open it in a scene that renders with Corona and the materials are still there, but the engine does not know how to evaluate them. You get a flat, wrong or black result.

That is why a good library labels every model with its engine. Before you download, filter by the engine your scene uses. When the model you need exists only for the other one, there is a decent workflow to bring it over, and it starts with the official converters.

The official converters

Corona ships with the Corona Converter. It converts the materials, maps and lights of a scene or of the selection to their Corona equivalents. It is available from the Corona tools in 3ds Max; its exact place in the interface depends on the version you have installed. Chaos provides the V-Ray Scene Converter for the reverse direction. Check the documentation of your version to see which Corona materials and maps it supports, because the list has grown from release to release.

Both are good at the common cases: a plain material with a diffuse map, reflection, glossiness, bump and opacity. They are not good at everything, and that is where the checks below matter.

Convert on a copy of the model, never on the only file you have.
Run the converter on the selected objects, not on the whole scene, to avoid touching materials you already finished.
Save the converted model as its own .max so the next project starts from the finished version.

What is usually lost or changed

The converters translate parameters, not appearance. After converting, always render a test with the same light and compare it against the preview. These are the points that fail most often.

Displacement: in V-Ray it is often a VRayDisplacementMod modifier on the object, while Corona uses a displacement map in the material. The modifier is not converted in every case, and the strength and the amount are not equivalent. Re-adjust it by eye.
Layered materials: a VRayBlendMtl with several coats does not map one to one to a CoronaLayeredMtl, and a car paint or a varnished wood often needs rebuilding.
IES lights: both engines read IES profiles, but the light objects are different (VRayIES or V-Ray lights on one side, the Corona Light on the other). Check the intensity and that the IES file path was found.
Special maps: dirt and ambient occlusion (VRayDirt and CoronaAO), edge and wire effects (VRayEdgesTex and CoronaWire) and rounded edges (Corona has a Round Edges map) behave differently. Multi-texture and colour-correction maps have equivalents, but the parameters rarely match exactly.
Proxies: a V-Ray Proxy (.vrmesh) does not become a Corona Proxy (.cgeo) by itself. If the model uses proxies, ask for the geometry, or convert them with the tools of the engine.
Procedural maps and the sky: scene-level elements, such as the sun and sky or the environment, should be rebuilt in your own scene rather than converted.

A workflow that works

Treat a converted model as a starting point. A routine that keeps the results predictable:

Merge the model into an empty scene that already has your render settings and a neutral light.
Run the converter on the model only.
Open Asset Tracking (Shift+T) and confirm that every map and proxy was found.
Render a test and compare it with the preview of the model, looking at reflections, glossiness and bump first.
Fix what is off, delete unused materials and save the result with a clear name, for example the model name plus the engine.
Merge the finished file into the production scene.

Work in a test scene with a dark grey background and one soft light. If a material looks right there, it will look right almost everywhere.

When it is better to rebuild the material

Converting is not always faster. If the material is simple, such as a fabric, a painted wall or a plain plastic, rebuilding it with the physical material of your engine takes two minutes and gives a cleaner result than a converted one with leftover nodes.

Rebuild when the material has a complex layer structure, when the displacement is essential to the look, when the converter leaves broken maps in the slots, or when the model will be reused many times. In that case a clean material is an investment: you will not fix the same issue in every project.

For plants, glass, car paint and anything translucent, expect to adjust by hand. For hard-surface furniture with standard materials, the converter is usually enough.

Prepare for the next time

If you work with both engines, or with clients who ask for one or the other, keep the finished conversions in your library next to the originals, and note the engine in the file name. A model converted once should never be converted again.

When you buy or download models, filter by engine from the start. Picking assets already prepared for the engine you render with saves the whole conversion step.