Confirm correct workflow: Getting basic GI working in mentalRay

#1

Greetings, all,

I’ve been revisiting the videos and notes from Jeremy Birn’s Lighting and Rendering class, in which I tried to participate way back in Fall of 2009. I’ve got quite a bit of free time right now, so I figured I’d try to bone up on my lighting and rendering knowledge, and revisit the lectures and excercises from Jeremy’s class.

For you veterans, could you please confirm, or shoot down, my workflow outlined below, please?

For you noobs, this may help you in an area that can be really confusing and loaded with variables, assuming the vets confirm the workflow is indeed a good one.

So, going through the basic Global Illumination process in mentalRay for Maya, I think I can summarize the workflow in the following steps:
[ol]
[li]Without GI turned on, get lights working as desired with direct shadows, light intensity, and falloff.[/li][li]Turn on GI[/li][li]Check “Emit Photons” for each light that should be evaluated for GI, and test render with default settings.[/li][li]Adjust photon intensity and test render to get the approximation of the final GI, looking very basically at color spill and indirect fill.[/li][li]Iterate until photon intensity gives the basic desired impression of the GI lighting[/li][li]Adjust number of photons to make the render less blotchy. Not too worried about completely eliminating blotchyness. Just trying to balance between render time and less blotchy.[/li][li]Turn on Final Gather, low intial settings (say…accuracy of around 64, point density between .2 and 1), to smooth the GI render[/li][li]Adjust FG settings to achieve final desired smooth image. Iterate as required.[/li][/ol]I also think I found out that settings for basic lighting and GI in mentalRay are highly dependant of the scale of a scene. I initially tried to recreate the basic lighting “room-in-a-box-with-a-lamp” scene from scratch, and found that even though my light and GI settings were identical to Jeremy’s tutorial settings, that my results were not even close to his. I switched, and used his supplied scene, and re-tried the renders, and viola! success. Using the measurement tool, I found that the scene dimensions of my scratchbuilt scene and the supplied scene were significantly different.

Software used: Maya 2009 Unlimited, mentalRay for Maya render engine

#2

I’m not a fan of photons, i find them reaaallly clunky and hard to adjust.

Final gathering is way more straight forward.

Build everything to scale, so your light fall off look right.

Make sure all your lights use physically correct fall off, and try not to use delta lights (point/spot).

I also find almost all GI solutions create to much bounce lights, so i still mult a bit of occlusion into my gi in comp.

#3

Agreed. I’ve used FG excusively in the past. I always thought the GI with photons in mentalRay for Maya was overly complex. But, I guess if you need more than one light bounce, it’s the way to get a more physically accurate render. Once I went through Jeremy’s lectures on the subject again, most of the settings made more sense and it is not as confusing as it initially seems.

And, yeah, falloff for lighting is pretty important. It is something that was completely glossed over in art school but makes a huge difference in the renders!

Thanks for the reply!

#4

I’m sorry, a delta light? That’s a term I haven’t heard before and how does it relate to GI/FG?

Thanks!
Zach

#5

a delta light is a “traditional” cg light light a point (omni), spot or directional light.

They’re bad because they are physically impossible (they have zero area)

#6

But, I guess if you need more than one light bounce, it’s the way to get a more physically accurate render.

You can have all the bounces you want with FG.

#7

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