27/02/2011

Vray speed tips for 3d visualisation

Here is a compiled list of tips that can improve Vray rendering speeds whilst maintaining a high level of quality. These tips come from my own experience, they may help improve your rendering, but they are not to be used as a definitive solution as every 3d project is different. I have categorised each tip to make it easier to follow and although some may seem obvious, I thought they should be mentioned as they can be useful.

Global switches

Geometry

  • When working with 3rd party CAD data, specifically Autodesk Inventor 3d files imported into Autodesk 3ds Max, leaving displacement ticked increases render times considerably. I assume this is to do with how it reads the mesh data. Obviously you will need to leave this on if you plan to have displacement in your scene, if not, turn it off.

Indirect illumination (GI)

Irradiance map

  • This GI method is resolution dependant, so adjust the min/max rate to suit your output resolution.
  • If you have multiple camera views for the same scene, save out an incremental irradiance map. The same map can be used providing there is over lapping geometry between camera views. This will save you some rendering time.
  • Tick show calc. phase, this will show you the irradiance map as its calculating. After a few seconds you will begin to get an idea of the general illumination of the scene. If it is incorrect you can cancel the render, therefore only wasting a small amount of time.

Light cache

  • Tick use light cache for glossy rays, this can reduce rendering times by quite a lot if you have heavy glossy reflections in your scene. Keep in mind that it is very dependent on the scene and because of this, in some instances it can lead to unwanted artefacts. There are multiple steps you can take to avoid this happening.

Option A

If you have the latest version of Vray (which is 2.0), there is an added feature called retrace threshold which improves the precision of the global illumination and helps eliminate light leaks when use light cache for when glossy rays is on.

Option B

Set the filter to fixed and adjust the filter size to two or three times the sample size. So if your sample size is 150 mm set the filter size to 300 mm.

Option C

Within a material, scroll down to the options panel and set treat glossy rays as GI to always. Also turn off the use light cache for glossy rays if you have it on. By doing this you are telling the material to always use the secondary GI engine to calculate the glossy rays, which in this case is the light cache. It basically does the same job as use light cache for glossy rays but you can specify which materials within the scene use this option.

  • Use screen as a method for scale when dealing with scenes that have large ground planes and distant objects. If you choose world scale, you may find that these distant objects can become very noisy, and you may decide to increase samples to remove this noise which will lead to longer render times.
  • Set your number of passes to the number of processor cores you have in your PC. Even if you have multiple cores over multiple PC’s, the light cache is only calculated on one PC.

System settings

Memory

  • By default, Vray sets the dynamic memory limit to 400, but this can actually go a lot higher. It is recommended to change this to a value that is half your RAM amount. For example if you have 8GB of RAM, you can set this to 4000.

Common

Image output size

  • It is important to understand render output resolution and DPI, Make sure you know what’s happening to the render once you have signed it off. If you have rendered an A3 image at 300 DPI and you then later on find out that image was going into a small area on an A5 leaflet, you have rendered your image at a higher resolution than what was required.

Render elements

  • Save out all your passes as separate files to later on composite them in post. This will allow you to tweak each individual aspect of your render such as lighting, reflection, refraction and shadow without the need to re–render the whole image again.

Image sampler

Antialiasing filter

  • Sharpening filters such as Mitchell-Netravali and Catmull-Rom may increase noise within the render, to compensate more samples are required to reduce the noise level. Turn the filter off completely and add it in post. Renders of around 3000 pixels are fine without a filter. Only use a filter when rendering smaller images to avoid antialiasing issues

Type

  • Adaptive subdivision is best used for flat non reflective materials such as buildings, whereas adaptive DMC is better and faster for glossy materials and camera blur.

Material editor

Reflect

  • When adjusting the reflective glossiness, you will need to increase the subdivs value to compensate, otherwise you will get very noisy results. Do not fall into the habit of setting the subdivs to a value you use throughout your scenes. Setting all your reflective materials to a subdivision of 32 for example, is not a solution. In fact it will increase your render times unnecessarily. Keep in mind that the higher the reflective glossiness, the lower subdivisions you can have. If you have reflective glossiness set to 0.85 you can set your subdivisions to 16 or even lower depending on your set up. If the reflective glossiness is set to 0.6, it would require a higher subdivision. This requires a little experimenting but it is good practice, especially for architectural visualisation, to have a default library of materials that you can use for multiple projects. This way, you won’t have to keep adjusting subdivisions because you know that material from your library is good enough.

Refract

  • From experience, adjusting the refraction glossiness does more harm than good unless you are aiming for a frosted effect. If not the majority of results are less than noticeable, and the render times are through the roof. Keep this at 1.0. You will save so much render time this way.

Vray materials

  • Vray calculates its own materials faster than non Vray materials because they are specifically optimised for Vray. A scene can easily be converted by right clicking the viewport and using the Vray scene convertor.

Preferences

Gamma and LUT

  • Without gamma correction, you are forced to add extra Vray lights in darker areas to further illuminate a scene causing the render times to go up. Gamma correction gives more luminance therefore fewer lights are needed. Within the 3ds Max preferences, enable gamma and set it to 2.2 and tick affect colour selectors and material editor. You will also need to change the Vray gamma. In the render setup under colour mapping set the gamma to 2.2.

To be continued…

If you have any questions about this post, or are in need of further explanation of any of the tips mentioned, please leave a comment below.

39 Comments

  1. peprgb on said:

    Great tips, did you notice the problem of Displacement when managing Autodesk AutoCAD data?

    Thanks!!

  2. jpcutler85 on said:

    I have never imported AutoCAD data, so I don’t know if it has the same issue as Autodesk Inventor files.

    Not yet come across a reason as to why it happens either.

  3. peprgb on said:

    Ok thanks. I made some test with Displacement on and off and it seems to work with same time in both cases ;)

    Best regards,

  4. super gnu on said:

    the comment about using the irradiance map for multiple views isnt right i dont think. the imap is view dependent so it only calculates the lighting for what you can see. you use the same saved imap for a different camera and youll have big problems with lighting errors.

    • super gnu on said:

      Hi James, yes ive used the various incremental add to map modes on many projects, and its true, you will get faster calculation of the second part of the map if there is an overlap of geometry between the two camera views.

      however this isnt the same as calculating a map for one camera then using it to render others. you must still add more irradiance caculations to the map in order to render another view. otherwise only the overlapping bits of geometry from the first view will have any lighting calculated for them. maybe you could just tweak your post to mention using incremental, as it is a good way to speed things up if you have multiple cameras that overlap on what they see. :)

  5. Hi, i have a question, do you think that the size of the texture files may be cause long render times??

    does the adress of the texture files when too long couse delay on rendertimes ??

    thanks for everything!!

    • Mike,

      The processing of textures has little to no effect on the render time, no matter what file size, format or name.

      The only time where render time may be effected is if you were to use complex displacement maps.

      Hope that helps

    • Normal maps would create a better bump surface as it holds more data.

      For example, a bump map holds single axis height information where as a normal map holds three axis height information.

      Normals maps give a much more realistic result.

  6. Mujeeb on said:

    Hi, James
    Thanks for the great tips and tricks

    I have serious concern about if we use in vray light in window for a light source for interior scene, what is the benefit if we switch on the sky light portal option, also the sub category ( simple ) can you please explain this.

    • Skylight Portal, if used will ignore the colour and multiplier of the light source and instead rely on the lighting of the objects behind it. This uses extra light rays to calculate so rendering times will be slower.

      If Simple Skylight Portal is used, it will only take light from the environment colour and will ignore any lighting coming from the objects behind it. This is a much faster way of using the Skylight Portal as no additional rays are calculated.

  7. hi,James
    I’ve a basic Problem…while rendering my scene in V Ray, I do not get the Status Bar (in grey-below the rendered output) which shows the current rendering settings & Time calculated for the render…Where am I supposed to get it from ??

  8. I have read new feature in Vray 1.5 SP5 that when we leave “0″ for Dynamic Ram rendering will use all the Ram you have. Is that a possible to setting up for render node in a farm ?

    Thank you,

    • What ever limit you choose it will use that limit for all machines in the farm. So if the dynamic memory limit is set to 4GB and a PC on the farm has 12GB it will only use 4GB of it.

      There has been discussions where by you change the limit to a percentage rather than a value. So you could set it to say use 75% of the PC’s resources. You can do this with a pre-render script.

  9. SANJEEV on said:

    Hi James,
    I happened to go thru ur tips on fast rendering.Great tips..if u could tell me the link to get the other half of ur tips,,,would be great,,Thanks a lot
    sanjeev

  10. Your one of a kind that ever did that. Keep it up. Reminder be aware when bringing in materials from different scenes as they may have the same name as materials already in the material list. Thanks

  11. 3D visualization are computer programs to create three-dimensional representations of natural or man made objects that can be manipulated, altered and efficiently communicated to others. Now technology is much better and there is a lot more to draw. As technology increases, the capabilities of 3D visualization are likely to increase as well.

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  13. V-Ray is a rendering engine that is used as an extension of certain 3D computer graphics software. The core developers of V-Ray are Vladimir Koylazov and Peter Mitev of Chaos Software production studio established in 1997, based in Sofia, Bulgaria.

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  15. abhishek on said:

    Hi, I want to know how does vray calculates scene geometry. Does it calculates the whole geometry of the scene or just visible in the camera? Like if I am working with the scene states will it calculate the scene state objects only or the whole file objects. I think it calculates the whole scene.

    • V-Ray loads the entire scene into memory as it performs all calculations in the scene space rather than what is relevant to the camera. However it does have both static and dynamic memory. Static memory is used by default and loads the entire scene at once. Dynamic memory allows V-Ray to swap in and swap out parts of the scene to save memory, thus why it is useful for things such as displacement. But if the entire scene was set to dynamic there would be a long wait for data to be loaded and unloaded, so a m mixture of the two methods is the most optimal solution.

      • abhishek on said:

        but if we hide objects that are not useful or used in other scene states might help in bringing down the render time, right?

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