View Full Version : Vray Rendering - Irradiance Map

03 March 2012, 03:07 PM
Hey all,

I am trying to render out a flythrough of a set I created using Vray. However, I continue to receive errors in my Irradiance map causing highlights to mist from the seams where 2 objects intersect. I have tried increasing the HSph. subdivs which solves the problem for the first frame but the error returrns and worsens with each following frame.

I am rendering with the irradiance map set the multiframe incremental and light cache set to flythrough. I have tried rendering the maps separately and loading them from file for the final render, as well as calculating everything during the same rendering.
Frame 01 - Clean
Frame02 - White appears around object on floor. Shadows behind object darken.
Frame 04 - Blotchyness occurs. Top of door is now lighter

min rate -4
max rate -3
Hsph. subdivs 250
interp. samples 20
clr thresh 0.3
nrm thres 0.1
dist thresh 0.1
Multiframe incremental

If anyone has any ideas on why this is happening I would greatly appreciate it, as this problem is begining to frustrate the hell out of me.


03 March 2012, 03:11 PM
your maximum rate is too low imho
And your subdivs are quite high

What are your dmc sampler settings?

03 March 2012, 03:33 PM
I found that when I set my maximum rate higher, to about -2 to 0 it would make the errors appear sharper.

For the subdivs , when I kept it under 100 I would still receive the issue. When I increased it, the error disappeared. At least for the first frame.

I was using adaptive subdivision not dmc, and my settings were -1 to 4.

Should I be using DMC?
Here is a render using DMC at 1 to 4 with Hsph. subdivs at 50

03 March 2012, 03:59 PM
I found that when I set my maximum rate higher, to about -2 to 0 it would make the errors appear sharper.
The errors get sharper with a higher maximum value because it increases the resolution, and thus detail) of the irradiance map. Sometimes its ok to use a low resolution, but in your scene you have some objects that have fine detail, so its better to use an irradiance map with according resolution.

So lowering the min/max rate wont help you get those splotches away, it will only make them bigger and thus you'll have bigger flickering parts in your animation.

I was using adaptive subdivision not dmc, and my settings were -1 to 4.
I was refering to the DMC sampler in the vray setting tab in the vray render dialog.
this one:
The irradiance map also uses the DMC sampler for its sampling.

You could try to set its noise treshold to somthing like 0,002 to 0,005. I find its default value of 0,01 is too high for most cases. Which results in splotchy irradiance maps and noisy dmc renders.
Also verry important here for animations using the irradiance map here is to make sure the time independent box is checked!

So in short:
- try higher irradiance min/max

- Dont use too much Hsph subdivs (250 is way too much for this scene). But dont go too low either (dont go below default 50)

- You could also try using a higher distance treshold in the irradiance map settings (the animation preset does this by default). So more samples are used where objects are close to each other.

- Lower DMC sampler's treshold, so your solution gets less noisy/splotchy.

03 March 2012, 09:47 PM
I'm feeling kind of dumb right now.
I got so focused on the IM settings because they seemed to effect the render the most that I didn't pay attention to the Light Cache setting. I played around with the LC subdivs, but never really touched the Sample size.

I just tried increasing the sample size and it solved the problem.

I do have a few more questions if you don't mind.

- For light cache, the subdivs control the amount of rays, the number of passes works in correlation with the number of cpu cores, but how exactly does sample size work?

What is the difference between setting it to flythrough oppose to single frame? I read that flythrough is the better choice for animations.

Lastly, whenever I tried to render out the light cache separately for my sequence it only rendered out the first frame(on flythrough). Should the light cache be calculated for every frame?

03 March 2012, 07:21 PM


03 March 2012, 07:35 PM
Thanks Critter,
I appreciate all the help

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03 March 2012, 07:35 PM
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