Material Settings

When setting up materials for StemCell there are some general setting that must always be used. These settings are necessary to maximize consistency and portability to other renderers. Setting up for V-Ray is pretty straight forward with a few minor adjustments. With V-Ray you will be using the VRayMtl material. Download the Calibration scene with example materials here, or below the example image.

Download Material Example Calibration Scene for these five material examples.

HGlossiness must remain locked so that RGlossiness is the only one affecting the render.

Fresnel reflections must always be on in order to achieve more realistic reflections.

Set IOR value for material within dielectric or metallic range for intended material using the same texture set. If multiple IORs of the same type, only dielectric or only metallic, are represented then set the IOR to the average of the IORs. The value difference between same material types is minimal in the render. IOR values can be set manually per material, but for this to work properly object grouping is very important. If multiple objects with varying materialistic properties are grouped together this method will not work as well. Reflect and Refract IOR values should never be two different values.

IOR values can also be set on the Refraction IOR settings as long as the Fresnel IOR is linked. Refractive materials must use only the Refract IOR.

BRDF type must always be set to GGX. This shading model provides the most physically accurate reflections for metallic materials.

Texture Map Settings

Texture maps must be applied to the right slots with the correct gamma. This section is a guide to correct material setup. You can also find the correct gamma types listed in the tables located in the Textures & Materials section of the StemCell 3D Modeling Specification.

Set all map contribution slots to 100.0 percent.

Make sure that all texture maps have Blur set to 0.01.

Plug the Diffuse map into the Diffuse slot. This is a sRGB map so it needs to be left on Automatic(Recommended) for bitmap gamma.

The Specular map needs to be plugged into the Reflect slot. This is a sRBG map so it needs to be left on Automatic(Recommended) for bitmap gamma.

If the model uses an Emissive map, this will be plugged into the Self-Illumination slot. This is a sRBG map so it needs to be left on Automatic(Recommended) for bitmap gamma.

The Glossiness texture map is going to be plugged into Reflection Glossiness/RGlossiness. This is a Linear map so it needs to use Gamma Override set to 1.0.

Apply a Normal Bump node to the Bump map slot, and plug the Normal texture map into it. Make sure Method is set to Tangent. StemCell does not accept Additional Bump maps, so do not use that slot. This is a Linear map so it needs to use Gamma Override set to 1.0.

When plugging in a Linear map make sure that Gamma is changed to “Override 1.0”. This applies to the Glossiness, Normal, and Refraction Map.

Transparent Materials

If transparent materials are present, they must follow the guidelines in How to setup Transparency & Opacity for StemCell.

If the model uses an Opacity map, this will be plugged into the Opacity slot. This is a sRBG map so it needs to be left on Automatic(Recommended) for bitmap gamma.

If the material uses Refraction, you may choose a value from the color picker that is Achromatic, meaning it possesses no hue information. The value used for Refraction Color should be Black, White, or a varying shade of Grey.

If the material uses a Refraction map, this will be plugged into the Refract slot. This map should also be Achromatic. This is a Linear map so it needs to use Gamma Override set to 1.0, shown above. Then set the other required settings for Refraction below.

Turn on “Affect shadows” check box in the Refract section’s settings.

Change the “Affect channels” option to “Color+alpha”.

What if my texture map set has multiple material types?

There are some situations where a material may require a dielectric and metallic materials on the same surface. See When to use Blend Materials for more information on these situations.

When an individual dielectric or metallic material can not be separated by object, that is the only time a blend material needs to be used. The Blend material is used to combine the 2 different IORs for dielectrics and metals. This way one material applied to the single object represents both surface types. A dielectric version of the material is created as Material 1 using correct low IOR value. A copy of that material is made for the metallic version as Material 2 with correct high IOR. The Metallic map is used as the Mask.

When plugging in your materials to the Blend material, typically the lower IOR material will be plugged into Material 1 while the higher IOR material will be plugged into Material 2. The two materials will then be blended together by adding the Metallic map to the Mask slot.