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.
- 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)
- 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.
- 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.
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.
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.
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.
- 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.
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.
- 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.
- 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
- 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.
- 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.
- 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 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.
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.