The Mental Ray engine is capable of producing stunning imagery, but, as with all raytracers, its processor intensive routines can mean some very long render times, which CGI artists are always looking to reduce. Here are a few of my favourite Mental Ray rendering tips, which can help speed up your workflow.
1 Area lights = soft shadows
When adding a new light to a scene, 3D packages will, by defalt, sometimes create a ‘point light’. This means that all its light rays will originate from a single, tiny point. Depending on the scene, this may not seem too much of a problem, but light photons radiating from a single point will always produce very sharp edged shadows.
There are several ways to solve this (using a ‘shadow map’ to fake a soft edge for example), but perhaps the simplest, most physically accurate way is to use an area light. Rays emmitted from a slightly larger area will cross each other and pass into the sides of the shadow area, producing a softer edge. Keep in mind the number of photons being used though, and that they need to be dispersed evenly from the whole light source area (so you may have to multiply them, lengthening render times).
2 Use Final Gather & highlights only
An easily overlooked but useful time saving feature of the Arch and Design material is the ‘highlights + FG only’ option in the Arch and Design material. When you don’t need an extremely accurate or clear reflection on an abject (eg. a gloss painted door), this option will provide great results with an enormous drop in render times.
3 Use CPU priority settings
Like all raytrace engines, Mental Ray is extremely power hungry. If your workflow tends to involve using your computer for other tasks while rendering, you’ll know how often it slows to a snail’s pace. There is a very effective way around this however. Call up your Windows Task Manager (press ctrl+alt+del or use Windows’ search function), and click the ‘processes’ tab. Right-click the 3ds Max in the list, highlight ‘set priority’, then click ‘low’. Now, all other tasks will take priority, while Max renders in the background, using only the power your other programs don’t need – effectively removing any slowdown.
4 Built in Ambient Occlusion
Gone are the days when we had to use a material override and a seperate render pass blended in Photoshop to achieve solid looking 3D. With the Arch and Design material, you can now adjust the strength, colour, reach and sampling quality of the AO from within each of your materials individually. This saves time and allows problem areas to be lightened or darkened in detail, rather than making do with a blanket covering using a full AO pass render. It can be found in the material’s ‘Special Effects’ rollout.
5 Fake Depth of Field
Depth of field is a photographic phenomenon that, where appropriate, can add greatly to the realism of a scene. It does, however, require an enormous number of extra calculations and is extremely processor intensive, adding greatly to render times. If your scene involves a view accross a horizontal area, with no objects standing vertically (something like the view across a book lying flat on a table top would work well), then faking the effect in Photoshop takes next to no time, and can look very convincing. Go to Filter, then Blur, and select ‘Tilt-Shift’. You can see some examples of this effect on the product renders on our CGI sample page.
I hope you find these tips helpful, and if you have any comments or tips to share with the world, come and visit our Facebook page or give us a tweet!