VRayMtl Overview

A special material - the VRayMtl - is provided with the V-Ray renderer. This allows for better physically correct illumination (energy distribution) in the scene, faster rendering, more convenient reflection and refraction parameters. Within the VRayMtl you can apply different texture maps, control the reflections and refractions, add bump maps and choose the BRDF for the material.

Diffuse

Diffuse Color  - this is the diffuse color of the material. Note: the actual diffuse color of the surface also depends on the reflection and refraction colors. You can either specify a simple color or use a texture.

Roughness - this parameter can be used to simulate rough surfaces or surfaces covered with dust (for example, skin, or the surface of the Moon).This parameter can also be textured.

Ex ample: The Roughness Parameter

This example demonstrates the effect of the  Roughness  parameter. Note how, as the  Roughness  increases, the materials appears more "flat" and dusty.

Roughness = 0.0  
 (regular diffuse material)

Roughness = 0.3

Roughness = 0.6

Opacity

Opacity color  - here you can assign opacity to the material where white is completely opaque and black is completely transparent. You can also assign a map by clicking the texture button. This way you can create a material that has a non-uniform opacity.

Reflection

Reflection Color  - reflection color. Note that the reflection color dims the diffuse surface color. This parameter can also be textured.

Example: The Reflection Color Parameter

This example demonstrates how the Reflection color parameter controls the reflectivity of the material. Note that this color also acts as a filter for the diffuse color (e.g. stronger reflections dim the diffuse component).

Reflection color = Black.
(0, 0, 0)

Reflection color = Medium Gray.
(128, 128, 128)

Reflection color = White.
(255, 255, 255)

Enable Fresnel reflections - checking this option makes the reflection strength dependent on the viewing angle of the surface. Some materials in nature (glass etc) reflect light in this manner. Note that the Fresnel effect depends on the index of refraction as well.

Lock Fresnel IOR  - allows you to unlock the Fresnel IOR  parameter for finer control over the reflections.

Fresnel IOR  - the IOR to use when calculating Fresnel reflections. Normally this is locked to the Refraction IOR  parameter, but you can unlock it for finer control. This parameter can be textured.


Example: The Fresnel Option

This example demonstrates the effect of the  Fresnel  option. Note how the strength of the reflection varies with the  IOR  of the material. For this example, the  Reflection color  is pure white (255, 255, 255).

 

 

Fresnel = On
 IOR  =  1.3

Fresnel = On
 IOR = 2.0

Fresnel = On
 IOR = 10.0

Fresnel = Off.

Lock highlight glossiness  - when this option is off you can enter different values for the H ighlight glossiness  and  Reflection glossiness . However this will not produce physically correct results.

Highlight glossiness  - this determines the size of the highlight on the material. Normally this parameter is locked to the  Reflection glossiness  value in order to produce physically accurate results.

Reflection glossiness - controls the sharpness of reflections. A value of 1.0 means perfect mirror-like reflection; lower values produce blurry or glossy reflections. Use the  Subdivs  parameter below to control the quality of glossy reflections.

Example: The Reflection Glossiness Parameter

This example demonstrates how the Reflection glossiness  and Highlight glossiness parameters control the highlights and reflection blurriness of the material.

Reflection/Highlight Glossiness = 1.0
(perfect mirror reflections)

Reflection/Highlight Glossiness = 0.8

Reflection/Highlight Glossiness = 0.6


Use interpolation  - V-Ray can use a caching scheme similar to the irradiance map to speed up rendering of glossy reflections. Check this option to turn caching on. See the Reflection interpolation section for more details.

Max depth  - the number of times a ray can be reflected. Scenes with lots of reflective and refractive surfaces may require higher values to look correct.

Subdivs  - controls the quality of glossy reflections. Lower values will render faster, but the result will be more noisy. Higher values take longer, but produce smoother results.

Enable dim distance  - enables the  Dim distance  parameter which allows you to stop tracing reflection rays after a certain distance

Dim distance  - specifies a distance after which the reflection rays will not be traced

Dim fall off - a fall off radius for the dim distance.

Affect Channels - Allows you to specify which channels are going to be affected by the reflectivity of the material

  • Color Only - the reflectivity will affect only the RGB channel of the final render
  • Color+alpha - this will cause the material to transmit the alpha of the reflected objects, instead of displaying an opaque alpha.
  • All channels - all channels and render elements will be affected by the reflectivity of the material

Reflection exit color  - if a ray has reached its maximum reflection depth, this color will be returned without tracing the ray further.

Refraction

Refraction Color  - refraction color. Note that the actual refraction color depends on the reflection color as well. This parameter can be textured.

Example: The Refraction Color Parameter

This example demonstrates the effect of the  Refraction color  parameter to produce glass materials. For the images in this example, the material has a gray  Diffuse color , white  Reflection color , and the Fresnel option is turned on.

Refraction color = Black
(0, 0, 0)
 no refraction

Refraction color = Light Gray
(192, 192, 192)

Refraction color = White
(255, 255, 255)


Glossiness  - controls the sharpness of refractions. A value of 1.0 means perfect glass-like refraction; lower values produce blurry or glossy refractions. Use the Subdivs parameter below to control the quality of glossy refractions. This parameter can be textured.

Example: The Refraction IOR Parameter

This example demonstrates the effect of the Refraction IOR parameter. Note how light bends more as the IOR deviates from 1.0. When the index of refraction (IOR) is 1.0, the render produces a transparent object. Note however, that in the case of transparent objects, it might be better to assign an opacity map to the material, rather than use refraction.

Refraction IOR = 0.8

Refraction IOR = 1.0

Refraction IOR = 1.3

Refraction IOR = 1.8


IOR  - index of refraction for the material, which describes the way light bends when crossing the material surface. A value of 1.0 means the light will not change direction. This parameter can be textured.

Example: The Refraction IOR Parameter

This example demonstrates the effect of the Refraction IOR parameter. Note how light bends more as the IOR deviates from 1.0. When the index of refraction (IOR) is 1.0, the render produces a transparent object. Note however, that in the case of transparent objects, it might be better to assign an opacity map to the material, rather than use refraction.

Refraction IOR = 0.8

Refraction IOR = 1.0

Refraction IOR = 1.3

Refraction IOR = 1.8


Use interpolation  - V-Ray can use a caching scheme similar to the irradiance map to speed up rendering of glossy refractions. Check this option to turn caching on. See the Refraction interpolation section for more details.

Affect shadows  - this will cause the material to cast transparent shadows, depending on the refraction color and the fog color.

Affect channels - Allows you to specify which channels are going to be affected by the transparency of the material

  • Color Only - the transparency will affect only the RGB channel of the final render
  • Color+alpha - this will cause the material to transmit the alpha of the refracted objects, instead of displaying an opaque alpha. Note that currently this works only with clear (non-glossy) refractions.
  • All channels - all channels and render elements will be affected by the transparency of the material

Max depth  - the number of times a ray can be refracted. Scenes with lots of refractive and reflective surfaces may require higher values to look correct.

Example: The Refraction Depth Parameter

This example demonstrates the effect of the  Refraction depth  parameter. Note how too low of a refraction depth produces incorrect results. Also, in the last two examples, note how areas with total internal reflection are also affected by the  Reflection depth .

Refraction depth = 1
Reflection depth = 5

Refraction depth = 2
Reflection depth = 5

Refraction depth = 4
Reflection depth = 5

Refraction depth = 8
Reflection depth = 5

Refraction depth = 8
Reflection depth = 8


Subdivs  - controls the quality of glossy refractions. Lower values will render faster, but the result will be more noisy. Higher values take longer, but produce smoother results.

Refraction Exit color on - if this is on, and a ray has reached the maximum refraction depth, the ray will be terminated and the Refraction exit color returned. When this is off, the ray will not be refracted, but will be continued without changes.

Example: The Refraction Exit Color Parameter

This example demonstrates the effect of the refraction  Exit color  parameter. This is mostly useful to show areas of deep refractions in the image, or for materials needing higher refraction depth. Note how the red areas are reduced when the  Reflection depth  and Refraction depth  are increased.

Refraction Exit color = Off
 Reflection depth = 5
Refraction depth = 5

Refraction Exit color = On
Refraction Exit color = Red
(255, 0, 0)
 Reflection depth is 5
Refraction depth is 5

Refraction Exit color = On
Reflection depth = 8
Refraction depth = 8


Dispersion  - this option enables the calculation of true light wavelength dispersion.

Abbe  - this option allows you to increase or decrease the dispersion effect. Lowering it widens the dispersion and vice versa.

Example: Dispersion

This example demonstrates the Dispersion capabilities of the V-Ray material and the effect of the Abbe parameter.

Dispersion = Off

Dispersion = On
 Abbe = 10

Dispersion = On
 Abbe = 50


Options

Trace Reflections  - check this option to enable reflections for the material.

Reflect on back side  - when this option is not checked V-Ray will calculate reflections for the front side of objects only. Checking it will make V-Ray calculate the reflections for the back sides of objects too.

Trace Refractions  - check this option to enable refractions for the current material.

Double-sided  - if this is true, V-Ray will flip the normals for back-facing surfaces with this material assigned. Otherwise, the lighting on the "outer" side of the material will be computed always. You can use this to achieve a fake translucent effect for thin objects like paper.

Cutoff - this is a threshold below which reflections/refractions will not be traced. V-Ray tries to estimate the contribution of reflections/refractions to the image, and if it is below this threshold, these effects are not computed. Do not set this to 0.0 as it may cause excessively long render times in some cases.

Env. priority  - this specifies how to determine the environment to use if a reflected or refracted ray goes through several materials each of which has an environment override.

Treat glossy rays as GI rays  - this specifies on what occasions glossy rays will be treated as GI rays:

  • Never - glossy rays are never treated as GI rays.
  • Only for GI rays - glossy rays will be treated as GI rays only when GI is being evaluated. This can speed up rendering of scenes with glossy reflections and is the default.
  • Always - glossy rays are always treated as GI rays. A side effect is that the Secondary GI engine will be used for glossy rays. For example, if the primary engine is irradiance map, and the secondary is light cache, the glossy rays will use the light cache (which is a lot faster).

Energy preservation mode  - determines how the diffuse, reflection and refraction color affect each other. V-Ray tries to keep the total amount of light reflected off a surface to be less that or equal to the light falling on the surface (as this happens in the real life). For this purpose, the following rule is applied: the reflection level dims the diffuse and refraction levels (a pure white reflection will remove any diffuse and refraction effects), and the refraction level dims the diffuse level (a pure white refraction color will remove any diffuse effects). This parameter determines whether the dimming happens separately for the RGB components, or is based on the intensity: Example

  • RGB - this mode causes dimming to be performed separately on the RGB components. For example, a pure white diffuse color and pure red reflection color will give a surface with cyan diffuse color (because the red component is already taken by the reflection).
  • Monochrome - this mode causes dimming to be performed based on the intensity of the diffuse/reflection/refraction levels. 

Example: The Energy Preservation Mode Parameter

This example demonstrates how the  Energy preservation mode  controls the way reflections dim the diffuse color.

Energy Preservation  =  RGB.

Reflection color = Medium Gray.
(128, 128, 128)

Energy Preservation  =  RGB.

Reflection color = Medium Green.
(0, 128, 0)

 

 

Energy Preservation  = Monochrome.

Reflection color = Medium Gray.
(128, 128, 128)

Energy Preservation  = Monochrome.

 

Reflection color = Medium Green.
(0, 128, 0)

BRDF

The BRDF parameter determines the type of the highlights and glossy reflections for the material. This parameter has an effect only if the reflection color is different from black and reflection glossiness is different from 1.0.

Type  - this determines the type of BRDF (the shape of the highlight):

  • Phong - Phong highlight/reflections.
  • Blinn - Blinn highlight/reflections.
  • Ward - Ward highlight/reflections.


Example: The BRDF Type

This example demonstrates the differences between the BRDFs available in V-Ray. Note the different highlights produced by the different BRDFs.

BRDF type = Phong

BRDF type = Blinn

BRDF type = Ward

Anisotropy  - determines the shape of the highlight. A value of 0.0 means isotropic highlights. Negative and positive values simulate "brushed" surfaces.

Example: The Anisotropy Parameter

This example demonstrates the effect of the  Anisotropy  parameter. Note how the different values stretch the reflections horizontally or vertically.

Anisotropy = -0.9

Anisotropy = -0.45

Anisotropy = 0.0
no anisotropy

Anisotropy = 0.45

Anisotropy = 0.9


Rotation  - determines the orientation of the anisotropic effect in degrees (rotation in degrees)

Example: The Anisotropy Rotation Parameter

This example demonstrates the effect of the Anisotropy rotation  parameter. For all the images in this example, the Anisotropy parameter itself is 0.8.

Anisotropy rotation =
0.0 degrees

Anisotropy rotation =
45.0  degrees

Anisotropy rotation =
90.0  degrees

Anisotropy rotation =
135.0  degrees

Anisotropy rotation =
Bitmapped 
map in the upper-right corner


Reflect Interpolation

These determine the options for the interpolation of glossy reflections. They are very similar to the options for the irradiance map. Note that it is not recommended to use interpolation for animations, since this may cause severe flickering.

Refract Interpolation

These determine the options for the interpolation of glossy refractions. They are very similar to the options for the irradiance map . Note that it is not recommended to use interpolation for animations, since this may cause severe flickering.

Material ID

The Material ID group is described here.

Maps

In this section the user can see all the parameters of the materials that can be textured and assign appropriate maps to them. Additionally the settings for bump mapping can be found here

Bump  - this option allows you to select a texture for the bump or normal map.

Bump amount - this is a multiplier for the bump map effect.

Bump map type  - this determines how the  Bump parameter is interpreted.