Chaos Corona for 3ds Max > [Max] Tutorials & Guides

Albedo vs render time

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maru:
Ok, here is the promised test with some more information. Its purpose is to check the relation between material's albedo and render time and consequences of adjusting scene exposure to new conditions.

How I made it: I started with a scene composed of a large room-like box, one camera, one Corona light and 3 objects.

There were 2 materials in the scene:
-01 - diffuse colour set to 255,255,255 - assigned to room object, the egg and the pony
-02 - diffuse colour set to 0,0,0 and reflection set to 0,5 to find out how different settings will affect reflections - assigned to the teapot

Corona light's intensity initially was set to 1.0.

Exposure compensation in Post processing rollout initially was set to 1.0.

Gamma initially was set to 2,2.

Material 01 initially had diffuse level set to 0,5.

MSI was set to 0 for an unbiased rendering. There were 15 passes for each rendering.

After each render I changed these values:
-material 01's diffuse level to 1/2 of previous value
-light's intensity to 1/2 of previous value
-exposure compensation to 2* previous value
-gamma experimentally to more or less match previous render's overall look

Note: I'm not sure if it was properly executed. For example: should I change material's albedo AND light's intensity and then double exposure compensation or ONLY material's albedo and then double compensation? Or maybe if I reduce by half the material's albedo AND light's intensity I should square exposure compensation??? I'm not smart enough for this so please correct me if I've done something stupid. :) Anyway, it gives some information on how changing albedo affects final output.

There is also one render with diffuse level of 0,8 and other values adapted accordingly.

The file names are as follows:

05x1x1.jpg

0,5 - diffuse level
1 - light intensity
1 - exposure compensation



00625x0125x8.jpg

0,0625 - diffuse level
0,125 - light intensity
8 - exposure compensation

etc

racoonart:
Thanks a lot for your effort maru! :)

I'm not sure but isn't this all about energy reduction? If you have a pure white material it will need way more bounces to be dark enough to be ignored - thus the very white materials are more noisy after a lot more time (since they are bouncing a lot more).
This afterall means that, as you're decreasing the intensity, bounces will decrease and you loose GI information.
(Again, this is just what I think this is all about ;)  )
You can see the increasing contrast (decreasing information) in the shadow areas. So, in my opinion, white areas should be white, but not too white to cause an unrealistic energy conservation, and not too dark to get ugly and (again) unrealistic contrasty.

Polymax:
Thanx for your job, very useful! I will keep it for myself.

Stan_But:
thanks for done job

maru:
Yeah, I forgot about conclusion but DeadClown basically wrote it for me. :) More whitness = more time to calculate bounces. More darkness = less time to achieve 0 energy. More darkness = more contrast and cool sharp shadows.

This made me think: maybe some more fakes would be useful? Like a "cutoff" that would stop calculating bounces after certain threshold is reached (or maybe this is already implemented? MSI?). This would be also useful for reflections, like in vray. But I don't even know if it would work with Corona.

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