Thierry’s Technical Tutorials

There are a few things that you must be aware of when rendering animations, that relate to the Mental Ray global illumination system.

You will probably be using final gather (FG) and global illumination (GI) when rendering your animation(s).

You can use ‘cache files’ that store FG and GI information between frames; this will save you significant amounts of render time, as well as reduce rendering artefacts.

Global Illumination

At the start of a render, depending upon the scene, Mental Ray may spend quite a lot of time producing the photon map. This does not change between frames, so it makes sense to only compute it for the first frame, and reuse it for all subsequent frames. Use a photon map file to do this.

‘Render’ dialog -> ‘Indirect Illumination’ tab -> ‘Caustics and Global Illumination (GI)’ rollout -> ‘Photon Map’ section:

1. Check the ‘Read/Write File’ check box.
2. Use the ‘…’ button to choose a file to write. (Use the ‘X’ button to clear a file from a previous session)

Final Gather

The final gather pass can also store information for use in subsequent frames. Final gather is not able to reuse all the information from previous frames, but it can reuse some. This means that using the final gather map file will save some time.
In addition to this, when using the final gather on either the draft, low, or medium quality presets, a flickering lighting-noise will be visible in the animation.
This looks extremely ugly. Using the final gather map file will almost eliminate these artefacts, so it is a necessary step.

‘Render’ dialog -> ‘Indirect Illumination’ tab -> ‘Final Gather’ rollout -> ‘Final Gather Map’ section:

1. Check the ‘Read/Write File’ check box.
2. Use the ‘…’ button to choose a file to write. (Use the ‘X’ button to clear a file from a previous session)

Anti-aliasing

Aliasing produces jaggy edges. Not only do these look a little bad in still frames, in animations these can look terrible.

‘Render’ dialog -> ‘Renderer’ tab -> ‘Sampling Quality’ rollout -> ‘Samples per Pixel’ section:

Minimum: By default, 3ds max uses a value of 1/4. This can result in small/thin object details being left out of the render entirely!! This causes flickering in animations so it can look very bad. Increase this to 1.
Maximum: The default value of 4 is okay, but the result will be better if you use 16. This will increase render time though; so what you use is up to you.

Mental Ray crashes

Using the final gather map will sometimes cause Mental Ray to crash, usually due to running out of memory.
If you render an animation from within Max, this will cause the render to stop. You will get an incomplete render; very annoying if you have left your machine rendering overnight only to discover that your machine stopped after 3 hours, and has done nothing since.
To overcome this, please read my tutorial on using Backburner.
Backburner will restart the render when Mental Ray crashes, so that you won’t lose any time.
This can make it very tempting not to use the FG map at all. This is not recommended due to the aforementioned noise-flicker artefacts.

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