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This page provides information on VRscans.
Page Contents
Overview
The VRayScannedMtl material applies material information gathered by the Chaos Group VRscans system to an object. The VRscans system captures the appearance of an actual physical material sample, going beyond single-point BRDF capture to faithfully represent the textured appearance of a real-world surface using bidirectional texture function (BTF) approximation. The information is saved in a .vrscan file, which the VRayScannedMtl material then reads to reproduce the material in the rendering.
The VRscans system and VRayScannedMtl material are intended as a solution for users who need to exactly match a given real-world sample.
The VRayScannedMtl material is designed to be used with a licensed version of the VRscans software. The material will still render without a license, but the material's UI will not display and any renderings will include a watermark.
The scanned material simply stores information about the way a physical material responds to light at individual points on the surface; it has no notion of components that extend across the surface such as diffuse or reflection qualities, or normal or bump maps. The scanned material is simply a faithful representation of how each point on the object responds to light. The .vrscan files tend to be quite large.
Currently, the material can render opaque and transparent surfaces. Also, aside from some general tint control, the material is unmodifiable; you can't change glossiness, increase reflectivity etc. You can only change the overall tint of the material.
For more details on VRscans, please see the VRscans documentation for information on downloadable sample scenes and Frequently Asked Questions, or visit the VRscans.com website.
UI Path: ||Material Editor window|| > Material/Map Browser > Materials > V-Ray > VRayScannedMtl
Parameters
General
File – The file name with the data for the scanned material; usually has a .vrscan extension.
Reload – Refreshes the .vrscan file loaded in the material.
Viewport UV borders – Displays the borders of the material tile in the viewport on the objects that have the material applied. This only works with the DirectX viewports.
Adjust UV tiling to an object – The .vrscan file stores information about the physical size of the scanned sample. By clicking on a point over a given object, the texture tiling is modified so that the texture is the correct size for the clicked point.
2-Sided – Forces the back-facing polygons to be shaded in the same way as the front-facing ones. If this option is disabled, the back-facing polygons will appear black. This can be useful for objects like curtains. Note that this option is always considered enabled when rendering transparent materials.
Disable transparency – Disables transparency for materials that store such information. This can be useful for speeding up the rendering, especially when the transparency produces little or no effect.
Effect ID – Specifies the Effect ID number.
Information – Displays some useful information contained in the .vrscan file, such as the actual material sample size.
Appearance
Filter Color – A color multiplier for the material sample and can be used to tint the material. (It will affect the color of the reflections as well. Acts as a post effect.)
Paint Color – Used to change the color of the material without losing the texture or changing the reflection color. For example, it can be used to changing the color of wood or leather without losing the material texture.
Gamma Correction – Adjusts the gamma of the material (including Filter Color and Paint Color if used) as a post effect.
Saturation – Controls the saturation of the material (including Filter Color and Paint Color if used) as a post effect.
Advanced
Subdivisions – Controls how many reflection rays will be traced for the material. Note that the material does not have a diffuse or reflection component and that everything is considered glossy reflection.
Trace depth – Controls the number of reflection bounces. A value of -1 means that the reflections bounces are controlled by the global V-Ray trace depth in the Global Switches rollout under the V-Ray tab in the Render Setup window.
Cut off – A threshold that is used to speed up reflections. If the contribution of reflections falls below this threshold, the reflections are not traced. This is similar to the Cutoff threshold of the VRayMtl material.
Don't use GI for rays shorter than – Defines the ray distance threshold below which GI caches will not be used to contribute for indirect illumination, but instead new secondary rays will be spawned. For example, if a ray hits any geometry that is too close to the ray's starting point, this will force the use of Brute Force GI for tracing additional secondary rays instead of using the GI cache.
Plain materials strategy – A strategy used for material display. It controls the visibility of textures (if present).
None – Used to view the material as it is with all the maps.
Average BRDF – Averages the BRDF and can be used to speed up the rendering for previews. Because texture details are removed, this also removes any tiling artifacts that might arise if the scanned sample does not tile very well. UV coordinates are still needed because most BRDFs are slightly anisotropic.
Average isotropic BRDF – Smooth representation of the material with no maps visible.
Scramble – Uses blocks from the photo samples in the material. Useful to reduce tiling artifacts for isotropic materials with small details like car paint with flakes.
Average BRDF – Averages the BRDF and can be used to speed up the rendering for previews. Because texture details are removed, this also removes any tiling artifacts that might arise if the scanned sample does not tile very well. UV coordinates are still needed because most BRDFs are slightly anisotropic.
Average isotropic BRDF – Smooth representation of the material with no maps visible.
Scramble – Uses blocks from the photo samples in the material. Useful to reduce tiling artifacts for isotropic materials with small details like car paint with flakes.
Color space – Specifies between sRGB, Adobe RGB, and Pro Photo color space models.
Don't use GI for primary rays – GI caches will only contribute to indirect rays. By default, this option is enabled (i.e. GI is not used for primary rays) to ensure better realism of materials. It makes sense to disable this option when the scene lighting is relatively even from all directions, as it will speed up the rendering but will likely cause no loss of image quality.
Uniform reflection distribution – When enabled, the material reflections are computed by sampling the hemisphere uniformly. When disabled, importance sampling is used to put more rays in directions where the material contribution is larger. One option does not always perform better than the other; performance depends on the scene lighting and the particular material that is used.
Edges Displacement – Uses a special technique that makes the edges of the geometry appear slightly jagged inwards. This option is useful when rendering close-ups of materials with bumps. It is faster than actual displacement and helps to achieve better realism.
Clearcoat
Enable – Enables the tracing of a clear coat layer for the material.
Highlights – Enables highlights from point light sources for the coat layer.
IOR – Determines the IOR of the coat layer, and from that controls the strength of the reflections. A value of 1.0 does not produce any reflections and disables the coat layer. Higher values produce stronger clear coat reflections. The .vrscan files typically contain the correct value for this parameter and it is set automatically when the file is loaded.
Bump multiplier – The coat layer has a built-in bump map stored in the material sample file. This allows you to control the strength of that bump.
Coordinates
This is a standard 3ds Max rollout used to control how the material is applied to objects.
This page provides information on the V-Ray Hair Material.
Page Contents
Overview
VRayHairMtl is a material that is primarily designed for rendering hair and fur. It can be used to render geometry generated through the VRayOrnatrixMod modifier, the VRayFur primitive, or the 3ds Max Hair&Fur modifier (when in mr prim mode).
© Ludovic Lieme
UI Path: ||Material Editor window|| > Material/Map Browser > Materials > V-Ray > VRayHairMtl
Components of VRayHairMtl
The material is based around three components - primary specular component, secondary specular component, and a transmission component. A diffuse component is also provided for rendering of materials made up of cloth threads or other non-translucent fibers.
The primary specular component represents light that is reflected off the outer surface of a hair strand. The secondary specular component represents light that goes through the hair strand and is reflected off the back surface. The transmission component represents light that goes through the hair strand.
The image below illustrates the meaning of the three components:
General Parameters
preset – Allows the user to choose one of several available preset materials. See the VRayHairMtl Presets example below for more information.
overall Multiplier – A common color multiplier for all color components in the material (except for opacity). Used to easily change the look of the entire hair material.
opacity – Controls the transparency of the material where white is opaque, and black is fully transparent. The opacity can be mapped along the hair strands using the VRayHairInfoTex texture. Making the hair more transparent towards the tip may produce more smooth and realistic anitaliasing at the expense of increased render times. If you map the tip opacity, make sure you don'tmake the strands thinner at the tip as well - transparency already creates the effect of thinning strands. You can enable the Opaque for Shadows and Opaque for GI options to reduce render times for transparent hair. Note that with transparent strands, it may be necessary to increase the Max. Transp. Levels option in the global V-Ray settings too.
Example: VRayHairMtl Presets
Here are some examples of the same hair geometry rendered with different presets. The scene is illuminated with one spherical V-Ray light, with GI set to brute force for the primary GI bounces, and light cache for the secondary, with retrace enabled.
Blonde (matte)
Brown (matte)
Blonde (shiny)
Brown (shiny)
Diffuse Rollout
diffuse – Controls the diffuse component of the shader. Use this for materials made out of cloth threads or other non-translucent fibers, as well as for dirty hair. Note that clean hair or fur does not normally have a diffuse component, so in that case leave the parameter black.
diffuse amount – Specifies the amount for the diffuse component of the material.
Primary Specular Rollout
The primary specular component corresponds to light that is reflected off the outer surface of hair strands (see the figure above).
primary specular – Specifies the primary specular color component. Normally this is dark gray.
Primary specular amount – Specifies a multiplier for the primary specular color.
primary glossiness – Specifies the glossiness for the primary specular component. Values closer to 1.0 make the hair more shiny and sleek. Lower values give it a matted look.
Secondary Specular Rollout
The secondary specular component corresponds to light that is reflected off the back surface of the hair strands.
lock to transmission – When enabled (the default), the color for the secondary specular component is derived from the color of the transmission component. Since a ray of light goes twice through the hair width, the color of the secondary specular component can be computed by multiplying the transmission color with itself. When this option is enabled, the hair color is mostly determined by the transmission color component.
secondary specular – Specifies the color of the secondary specular component. If Lock to Transmission is enabled, this value is ignored, and the secondary specular color is derived from the transmission color.
secondary specular amount – Specifies a multiplier for the secondary specular component. If Lock to Transmission is enabled, this value is ignored, and the secondary specular amount is derived from the transmission amount.
secondary glossiness – Specifies the glossiness for the secondary specular component. Values closer to 1.0 correspond to shiny and sleek hair. Lower values correspond to matted hair.
Transmission Rollout
The transmission component corresponds to light that goes through the hair strands.
transmission – Specifies the color for the transmission component. When Lock to Transmission is enabled, this color determines the overall hair color.
transmission amount – Specifies the amount of the transmission component.
transmission glossiness length – Specifies the glossiness of the transmission along the hair strand length. See the Transmission Glossiness Length and Width Parameters example below for more information.
transmission glossiness width – Specifies the glossiness for the transmission component across the hair strand width. See the Transmission Glossiness Length and Width Parameters example below for more information.
Example: Transmission Glossiness Length and Width Parameters
This example shows the effect of the Transmission Glossiness Length and the Transmission Glossiness Width parameters. It shows a number of vertical strands (in this case, produced by VRayFur) lit from behind by a spherical light.
Note how each parameter changes the way light scatters along the length and the width of the strands. Higher values for the length glossiness compress the transmission highlight along the strand length, while lower values expand it.
Length: 0.85
Width: 0.95
Length: 0.98
Width: 0.87
Options Rollout
opaque for shadows – When enabled, the hair material is always opaque for shadow calculations. This speeds up the rendering of transparent hair.
opaque for GI – When enabled, the hair material is always opaque for GI calculations. This speeds up the rendering of transparent hair.
simplify for gi – When enabled, a simplified diffuse version of the BRDF is used for GI calculations. This may speed up the rendering of hair but may significantly change the final look.
use Cached gi – This option is similar to the Use Irradiance Map option for the VRayMtl material; if it is disabled, the hair material will always be calculated with brute force GI.
Example: Effect of GI on Hair
This example shows how important GI (multiple scattering) is for the appearance of hair, especially bright hair. The top row shows several of the presets rendered without GI, and the bottom shows the same scene when GI is enabled. Again, GI is brute force and light cache has retrace. The scene GI environment is black so that a spherical area light is the only light source.
Example: Strand Taper vs Transparency Mapping
This example shows how transparency mapping can be used to simulate hair thinning towards the tips with improved quality. Since transparency also increases render times, the VRayHairMtl material provides two options to optimize this - the Opaque for Shadows and Opaque for GI options allow to skip the transparency calculations for shadow and GI rays, thus speeding up the rendering.
For the first image, the thinning of the strands towards the tips was done by setting the Taper parameter of VRayFur to 1.0. The opacity of the hairs for the 2nd, 3rd and 4th image is done with the VRayHairInfoTex texture in the Opacity slot of the VRayHairMtl material, while keeping the Taper parameter in VRayFur to 0.0. The scene is illuminated with one point light with sharp raytraced shadows to better show the difference between the options. Note how opacity mapping improves the antialiasing of the hair, while still preserving the same overall look, at the expense of somewhat increased render times. However, the first image also required increased AA samples compared to the rest.
Note that using transparency for the strands may require increasing of the Max. Transp. Levels option in the global V-Ray settings, although it was not necessary for this particular case.
Hair geometry without taper, with opacity mapping.
Render time: 2m 14s
Hair geometry without taper, with opacity mapping, both Opaque for Shadows and Opaque for GI enabled.
Render time: 1m 46s
Hair geometry without taper, with opacity mapping, Opaque for GI enabled,
Render time: 1m 57s
Maps Rollout
The parameters in this section allow the various components to be mapped with textures. The Hair Information Map | VRayHairInfoTex texture can be used for mapping a parameter along the strand length or to get the color from the 3ds Max Hair & Fur modifier.
Advanced Rollout
light multiplier – Specifies a multiplier for the effect of direct illumination on the current material.
Notes
- The preferred method for rendering objects with the VRayHairMtl material is with GI enabled, Primary Engine set to Brute force, and the Secondary Engine set to Light cache with the Retrace Threshold enabled. Because of the fine details in hair objects, the irradiance map may produce too much flickering in animations.
- Global Illumination is vital for realistic rendering of hair, especially with bright hair color.
- Proper gamma workflow is essential for realistic rendering of hair.
- To apply the VRayHairMtl material to a 3ds Max Hair & Fur modifier, use the mr Parameters section as described here.
References and Links
Here is a list of links and references used when building the VRayHairMtl material.
[1] J. T. Kajiya, T. L. Kay, Rendering Fur with Three-dimensional Textures, SIGGRAPH'89: Proceedings of the 16th annual conference on Computer graphics and interactive techniques
Presents one of the earliest shading models for rendering hair.
Presents one of the earliest shading models for rendering hair.
[2] S. Marschner, H. W. Jensen, M. Cammarano, S. Worley, P. Hanrahan, Light Scattering from Human Hair Fibers, SIGGRAPH'03
An online version of this paper can be found at http://graphics.stanford.edu/papers/hair/
Introduces a three-component shading model for hair which produces quite realistic results, but is somewhat difficult to control.
An online version of this paper can be found at http://graphics.stanford.edu/papers/hair/
Introduces a three-component shading model for hair which produces quite realistic results, but is somewhat difficult to control.
[3] I. Sadeghi, H. Pritchett, H. W. Jensen, R. Tamstorf, An Artist-Friendly Hair Shading System, SIGGRAPH'10
An online version of this paper can be found at http://www.disneyanimation.com/library/a56-sadeghi.pdf
Simplifies the three-component model from [2] and makes it easier for users to adjust the separate components.
An online version of this paper can be found at http://www.disneyanimation.com/library/a56-sadeghi.pdf
Simplifies the three-component model from [2] and makes it easier for users to adjust the separate components.