B/W Blurred Spots

[dopeich2]

Hi, i'm testing some frontal renders of a door, and on the large flat grey surface appear some black and wihte spots like blurred (if you see the image from far, it will be worse).

The image:


My settings:

IRmap Medium, Hsph subdivs = 60, interp.samples= 20
LightCache, 1200 subdivs, sample size= 0,02 (screen), 2 passes (dualcore)

Adapt QMC sampler, min/max at 1/5
rQMC Sampler adaptative amount 0,95, noise thr 0,003, min samples 16. multiplier = 2

Questions:
- Should I change to adaptive subvs sampler?
- Has it anything to do with the light cache?

Thanks for the help.

[^Lele^]

There are a zillion posts dealing with this sort of non-issues in the forums.
Please use the new and powerful forum search function ("irmap splotch" as keywords.).

[vlado]

Looks like you need to increase the Hemispheric subdivs for the irradiance map and/or decrase the DMC Sampler Noise threshold.

Best regards,
Vlado

[dopeich2]

Great!, I had to rise the Hsph subdivs up to 150-200 depends on the color (darker ones are less affected).

Thanks very much vlado, congratz for the work.

[^Lele^]

In fact, there is no need whatsoever to increase the Hsubdivs in this particular case.
It's one of the options, but in my opinion not the best one.
Vray's shown to do a MUCH better job at this if you just DECREASE the min sampling rate for the irmap to something like -7, leaving the max to whatever you had, and most importantly leaving the subdivs to the default.

That's guaranteed to get you a clean result, provenly so.
(check those infamous posts on the forum for feedback.)

[vlado]

Lele, this would simply makes the splotches larger and so less noticeable.

Best regards,
Vlado

[^Lele^]

Which is exactly what one would want in an evenly lit, flat surface, isn't it?
Raising hsubdivs of course raises the sampling, and will eventually clean it up "correctly", but the rendertimes can become huge.
Refer to this thread as to the kind of results lowering min rate has on renders (err, i suppose you of all people know, but hey, it's a debate, so i'll take you for a "common user", Vlado, please humour me )

http://www.chaosgroup.com/forums/vbu...=irmap+splotch

Here's how the irmap will behave in a normal case (default to high), and with the same settings but a min of -6.
The first image took 18 seconds for the GI to compute, the second only 11. and it is cleaner.

[vlado]

Well, I suppose it depends The problem will still remain in corners where the samples are closer.

Best regards,
Vlado

[^Lele^]

ah yes, indeed.
The difference in raising hsubdivs once VRay has only got the corners to deal with, though, is a lot less rendertime-impacting than doing so with a default preset, and to me it feels like VRay's doing a better job at it.
Of course, if the scene is Greeble-like, with plenty of crevices, then you're right, just use defaults and raise hsubdivs.

[Da_elf]

the help file online has some great advice on the different lookup methods and interpolation methods