VRay – Multi matte

Multi matte, colored alpha, color mask there are alot of different names for this technique. The vRay multi matte render element lets us easy and with relative little effort setup a multi matte. To use the multi matte do the following.

Using shader to define ID

• On the shading group enable atributes>vray>Material ID and set it to an int.
• In the render setting add a multi matte render element.
• In the multi matte render element be sure to enable the use material id checkbox to make use of the mat id we setup in the first step.

To use more than r, g, b add another multi matte render element.

Using object id to define id

this can be done on single object and multi.

Single object

• on the object shape node add attributes>vray>object id set id to an int.
• add a multi matte render element.
• set the object id to corresponding int.

Multi objects

• select the object you wish to separate.
• create>vray>apply single object proprties node to selection
• set the object id of the single object properties node
• add render element, use corresponding object id.

VRay Basics – wip

Image Sampler

Adaptive DMC – Deterministic monte carlo

Best for:

• Detailed textures
• Lots of geo detail
• Lots of blurry || gloss effects

> min/max: of sampling: cannot go lower then 1 on the min. Will sample every pixel at least 1 time.

> Threshold: when to use min / max sampling

Adaptive Subdivision

Best for:

• Smooth scenes
• Few blurry || glossy effects
• Smooth textures

> Min/max: allows for subsampling.

Fixed Rate

Best for:

• Complex scenes
• Lots of blurry || gloss effects
• Detailed textures

Light Atributes

Sampling

Light cutoff threshold: Below this threshold the light contribution will be ignored.

Shadow

Shadow bias: shifts (toward / away)  the shadow in respect to the shadowcasting object.

GI

When working with GI it can be a good idea to use the Adaptive DMC sampler type

Brute force GI

• Accurate
• slow – takes all shaded point into account
• can generate a noisy result
• Seldom used as the primary GI engine, could be used for secondary bounces.

> Subdivs: Image quality higher value less noise longer render time

> Depth: number of bounces of rays. Won´t have an effect if used as Primary bounce engine.

To decrease the noise we can increase the subdiv of the brute force.

Photon mapping

• Mainly used as secondary engine
• Photon is generated by a light source ( like GI in MR )
• bounces around in the scene and gathers information
• Best used in an enclosed space, sine it bounces on geometry to gather info

Workflow set the Photonmap to priamry and do the adjustments. Then set it to be the secondary render.

> Bounces: Number of photon bounces. The total number of photons in the scene is a result of the number of initial photons cast by the light and number of bounces set in the render global. When a photon hits a wall it is “left behind” and a new one is cast into the scene.

> Max Photons: The max number of neighbouring photons to be used to generate an averaged intensity i.e a smooth result.

> Prefilter: Generates a smoother result

> Convex Hull Estimate: Can help to alleviate rendering artifacts in corner areas.

> Store Direct Light: When disbaled the photon will only carry secondary light info. May keep more detail in shadow areas, sine it will not be smoothed in the GI calculation. When enabled render can be faster, be may lead to loss in shadow areas.

> Auto Search Dist: When enabled will let Vray decide the distance in which we search for neighbouring photons to be averaged. When disbaled we can explicitly specify that dist. Related to the scene size. lower dist more detail, higher dist more smoothness.

> Multiplier: Multiplier of the GI

> Retrace Threshold: Instructs Vray to use more of a brute force method when calculating the gi result in problem areas like corners. When we set the threshold to 90 it will use this feature in staright corners. When set to zero it will be igmored.

> Max Density: Will discard photons that are really close to each other. May lead to faster rendertime and less artifacts. Could also mean less deatil.

Irradiance Map (compare to FG in MR)

Meant to be used stricktly as a primary bounces engine.

Rays are cast from the camera into the scene. Irradiance works for enclosed scenes but also outdoor senes with larg distances and open space.

Basic Parameters

> Min Rate: The minimum of smaple points used. Vray will start using the min value but if it finds that it needs more sample it will continue doing so until it reaches the max value.

> Max Rate: The maximium sample points used.

> Subdivs: The number of rays cast from each sampl point.

> Interp. Samples: The number of  samples used to average the result. More points = smoother, less detail, Less points can lead to splotchyness, noise.

> Interp. frames: Number of frames to be used to average the result. Used in animted sequences to help alleviate flickering

Light Cache

Intended to be used as the secondary engine.

Best used in an enclosed space. Caompare to photonmapping BUT rays are sent from the camera not the light.

> Number of Passes: Number of threads on the CPU. If you have 8 cores, set it to 8.

> Subdivs: squared (pow)  Rays shot from the camera.

discussed on aweidenhammer utube channel. Recommended 1500 for a full HD render.

> Sample Size: Tell vray to discard samples close to eachother. This controls the distance of where this happens.

Reconstruction Parametrs

> Filter type: If used as the prinary bounce engine set the filter type to fixed if used as the secondary engine use nearest.

DT recomendation

indoor scenes

Primary: Irradiance map

Secondary: Light cach

Outdoor scenes

Pramary: Irradiance

Secondary: Brute Force

Mel & Python

I am on a mission to swtitch from Mel to Python as my language when I work in Maya. The reson being that Python is a much more powerful language to use. But when you are used to a language and switch to something that you are less familiar with even the simplest task take longer time. The code below shows something that tripped me up a little bit. The feedback that I get from Python and Mel is a bit diffrent. The code below gives the variable sel a string that is the name of a nurbs sphere in the scene. In the scene I have to objects named ” nurbsSphere1″, one is at the scenes root level and one is parented in a group. This makes it possible that the two objects share the same name. But when I use Mel to select the sphere I get the error that two objects have the same name. But in Python I get the error that the object is invalid. It took a  few minutes before I figured this one out. So just keep this difference in mind.

MEL example

string $sel = "nurbsSphere1";
select $sel;

// Error: More than one object matches name: nurbsSphere1 //

Python example

sel = 'nurbsSphere1'
mc.select(sel)

# Error: TypeError: Object nurbsSphere1 is invalid #