This page lists a number of frequently-asked questions about V-Ray.
General Questions
What is the difference between a pixel and a sample?
The pixel is the smallest addressable element of an image. The main task for any rendering engine is to determine the color of each pixel. In order to do that, it has to take samples from the scene. Samples are small units of information about a certain point in the scene that the rendering engine uses to determine the color of each pixel. One or more samples can be taken for every pixel in the image.
What is the difference between primary rays and primary bounces?
Primary rays are those coming directly from the camera. Primary bounces occur when a ray from the camera first reflects (usually diffusely) from the surface of an object.
Materials and Maps
How can I render a wireframe with V-Ray?
You can use the VRayEdgesTex texture to get a similar (although not exactly the same) result.
How do I use an HDRI map with V-Ray to illuminate the scene?
Either load it in a VRayDome light or load it as the Environment map in the Environment window (if it should be shown in the background).
Global Illumination
Why does the HDRI map have no effect on the specular level of the rendered objects?
With the standard 3ds Max materials, the specular level is just a way to simulate a shiny look for objects. For a real-world object to be shiny, it has to be reflective. The same applies for objects rendered in V-Ray. To achieve a shiny look with V-Ray lights, glowing objects and environment maps, you need to make the objects reflective.
Why do I get very weak shadows produced by the HDRI map?
The HDRI map needs a very high dynamic range to produce sharp shadows. You might need to replace the HDRI map that you are using with another one with a larger range.
How can I set the IOR when I use a Standard material with VRayMap for refractions?
In the Material Editor, set the Index of Refraction in the Extended Parameters rollout for the material.
What GI Engine(s) should I use for my scene?
In most situations, using Brute Force for your primary engine and Light Cache for your secondary will give you the best ratio between quality and speed in terms of not having to tweak a lot of GI settings to get a nice result. The render will have clean light bounces from accurate GI calculations, with minimal blotchiness or flickering for animated sequences.
Why do I get loss of detail when I render an object with lot of detail using Irradiance Map?
Increase the Max Rate. For example, set it to 0. You may also try to reduce the color and normal thresholds. Additionally, to make the GI produced by the Irradiance map more detailed, you can reduce the interpolation samples.
Irradiance Map GI engine is deprecated. It doesn't support some of the new V-Ray features and will be soon removed as an option.
Does the antialiasing filter affect the irradiance map?
(Can I calculate an irradiance map with one filter and then use it with another?)
No, the irradiance map is not affected by the anti-aliasing filter. In fact, to compute an irradiance map, rendering without anti-aliasing and without a filter is possible. Add these later on for your final rendering.
Can I render the irradiance map at 400x400 and then use it to render a 800x800 image?
(What will be the effect?)
Yes, that's fine. The final effect will be as though you have computed the irradiance map at a lower sampling rate.
Why does my fog light the scene when I use V-Ray with GI?
This happens because of the way the 3ds Max standard fog is implemented. It is self-illuminated (unless you use volume light, but standard fog and volume fog are self-illuminated), and since V-Ray takes volumetrics into account when calculating light hitting surfaces for GI, you can see illumination coming from those volumetrics.
Rendering
I have a dual CPU system, but the rendering seems not to be multithreaded. How can I implement multithreading?
Check the Multithreading option in 3ds Max's preferences - Customize > Preferences > Rendering > Multi-threading. Make sure this is On.
When I render a particular object with the V-Ray renderer, dark rectangles appear at odd places on the object.
(When I render the same object with the Max default scanline renderer, the dark rectangles disappear.)
This could happen if your object is a thin box with overlapping faces. Increase the Height or remove the overlapping faces and the squares should not appear in the rendering anymore.
Rendering one scene using different-sized regions result in significantly different render times but no difference in quality.
There should be no difference in the final image, no matter what is the size of your render regions. However, every region requires some setup time. Also, when you use anti-aliasing filters, there is a border around each region that needs to be additionally rendered so that the edges of regions blend smoothly. As the region size increases, this additional work takes less time compared to the total render. Smaller regions allow for faster screen update - you can see your image in progress; regions save memory; regions allow easy multithreading and (more important) easy distributed rendering. The choice of slowdown/update rate is best left to the user. Values of 16-64 are recommended.
Distributed Rendering
Will the distributed engine upload the complete scene to every machine including textures, etc.?
(Or will each machine just receive what is needed to render its bucket?)
It will ship the full scene without the textures. This means the textures must be visible from all the local machines, but there is no need to share the scene itself.
Can I easily change the task priority for all machines that participate in distributed rendering?
Yes, this is configurable. The process priority can be controlled remotely for each rendering server. For more information refer to the Set Up Distributed Rendering section.
Is the "machine list" in the distributed rendering based on machine names or IPs?
It is based on machine IPs. Names can be given to each machine and they don't have to be the same as previous network names. The important part is a valid IP. There is an autosearch mechanism which looks for all the available servers in the local network and includes them in the list. A box can be configured manually.