Posted: Mar 02, 2012
Published by: the area
Homepage: Visit the page
Software: Autodesk 3ds Max, Autodesk Maya, Autodesk Softimage
Category: General, Rendering
Rendering animations using Vray can undoubtedly leave you in frustration when it comes to render times. The high gloss materials, reflections and displacements that you use for still images can make your total animation rendering time beyond manageable.
Using displacement in still images is a slow process. When it comes to animation this process becomes far more complex and usually involves careful planning, especially if you need to keep that carpet looking like carpet.
For areas such as grass and carpet, use 3d mapping. The textures for the 2d mapping will need to be loaded for each frame and if the texture maps are large this will take some time. For carpet and grass, the edge length for 3d mapping can be set quite high and still look good. The lower the edge length, the more Vray subdivides the mesh and this increases the render times. Edge length is resolution dependant, the higher the resolution, the higher this value should be. You should also make sure that the view dependent option is enabled. This can reduce flickering due to the quality of the displacement being spread much more evenly.
In order to keep the render times low, you usually sacrifice the quality of your subdivisions for lights and materials which in turn introduces noise.
By using sharpening filters such as Mitchell-Netravali you are introducing more noise into the render on top of the noise already created via the low subdivisions for lights and materials. Try to use blurring filters such as area instead. It will generate less noise and help blur out the noise that already exists.
The biggest slowdown of all is glossy reflections within your materials. There is no escaping using them if you want your materials to look realistic.
Keep the glossy reflection range between 0.7 and 1 and adjust the subdivisions accordingly. Chances are that within a animation lower glossy values will go un-noticed. If the result is satisfactory you can use light cache for glossy rays and then the calculations for glossy reflections will be much faster.
Surrounding objects are important for reflections and refractions. The max depth determines how much of these surrounding objects are used within the calculation.
Lower your max depth values to 3 or 4. When a reflection or refraction can no longer be traced it will look to the exit colour. You would set the exit colour to a similar colour to the material that it is reflecting and/or refracting. You can control this individually for each material or in the global settings.
Vray slows down as more objects are introduced into the scene that are contributing to GI.
For objects such as trees in the background, exclude them from receiving and generating global illumination and shadows.
Not everything has to be on during the pre-calculation of the GI.
Displacement can be turned off when pre-calculating the irradiance map and light cache. Turn it on when you do the final render.
You may have areas within a scene that are not visible in the first few frames but are visible later on. Leaving these objects visible for the whole animation will certainly keep your render times high.
Plan your scene, use layers and group them accordingly. If there is an upper floor of a building that does not come into view whilst on the lower floor hide it completely. The chances of it contributing the reflections and/or refractions of the lower floor are small. Break the animation up in to small sequences and use multiple cameras.
Shadows and glossy materials are controlled by subdivisions. A low subdivision gives higher noise and a high subdivision leads to longer the render times.
For animation, subdivisions can be lower than they would be for still images. There is much more going on in the scene, i.e. moving object’s and cameras. A little extra noise will go un-noticed.
Large complex scenes require a lot of system memory to store all the information for rendering.
By using Vray proxies you will free up memory for other calculations. If you stay within the memory limit you won’t actually speed up rendering by using proxies. Once the memory has been used up, 3ds Max and Vray will start to use the system page file. This is when the rendering starts to slow down.
Vray uses dynamic memory and static memory to calculate various processes. These two processes can play against each other over the available system memory.
Processes such as displacement use dynamic memory. For heavy scenes that have displacement you can increase the dynamic memory limit to help the rendering process. Increase the default value to around half your available system RAM, memory must be kept free for other processes. Keep in mind that by increasing the dynamic memory limit you are reducing the amount available for the static memory.
James Cutler is a 3D Digital Designer and founder of MintViz, a creative consultancy that provides tutorials, tips and resources for the CG industry.
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