FG blotches - how to get rid of them?

[pdesopo]

Hi,

I'm doing my brief steps trying to get a better knowledge of Softimage. One of the most struggling challenge so far it's been Final Gather. Even though I'm following tutorials still I cannot fully understand how it works when it comes to produce a clean image. To better explain the issue I'm experiencing, I've attached a bunch of images where you'll notice very annoying blotches I'm pretty sure due to my FG settings.
The same settings work fine in other circumstances and I see that's due to the nature of FG itself as it mimics an accurate calculation of the light being FG physically correct, i.e. each scene needs different FG settings. That's what I've got theory wise so far: with the hope that's a correct assumption, I'm totally missing a practical translation to better handle a proper FG setup.

P.S. the main differences in the attached examples is that I've used MIA by Felix for the room, and in that case I'm getting even more blotches.

[Maximus]

Try Increase the points number and see the difference.
You might want to switch to "Automatic" mode instead of Multiframe.

When you see artifacts/blotches or speckles try using the filter size at 1. Leave it at 0 if you dont experience those problems.
You need to do a lot of testing, there isnt a precise settings on FG thats why it sucks. It is fairly and very inaccurate to produce correct illumination, its a pain to work with it, so get ready to suffer

[pdesopo]

Try Increase the points number and see the difference.
You might want to switch to "Automatic" mode instead of Multiframe.

When you see artifacts/blotches or speckles try using the filter size at 1. Leave it at 0 if you dont experience those problems.
You need to do a lot of testing, there isnt a precise settings on FG thats why it sucks. It is fairly and very inaccurate to produce correct illumination, its a pain to work with it, so get ready to suffer

Thanks for helping out Maximus.
As far as I remember I tried several values for points and it wasn't getting any better. I didn't tried Automatic nor I changed the filter size to 1, so as next step I'll surely try that.

I'm a bit confused about the last part of your post as I'm sure my trouble comes from my inexperience with MR but it seems from what you're saying that even though I would gather experience that doesn't mean the process will be straight forward. Is this the reason why I hear people complaining about MR or is there something else?

edit: I hope it just can gets better as when it works (i.e. when I probably do it the right way), I really love it!

[Maximus]

I can tell you from my experience with it, its totally random.
I like mental ray for many things, but i do really hate its Global Illumination system, i think its outdated, poorly implemented and inaccurate.
Of course i might be wrong and you will find stunning works done with mental ray around the web. But as i said that was my experience.

Final gathering is a lottery, it depends on many factors, there are a lot of things that can mess and create artifacts with it.
Thats why it really comes down to what are you doing, what is your scene setup and how you using a lot of things, from shaders to environment lighting, and the whole lighting setup you are using in your scene.

Most people complain about mental ray abouit precise things like: GI, displacement, motionblur/dof, instancing (proxy), integration from AD into packages.
I personally can live with everything but i really do hate the whole GI system in mental ray, it makes you go insane.
If you can share the scene i can take a look and help you further, try using the normal architectural material for now, the advanced one might have some issue (i remember having issue with photons when i used it) dunno if it got fixed.

[Kzin]

there are some things you have to know about fg.
first, fg needs alot of diffuse light to work best.
second, dont use high contrast maps to illuminate your scene.
third, fg is not best for detail gi solutions. for this, use ao mode in the mia_mat to capture details, or better but with higher rendertimes, use the colorbleed feature.
fourth, use only mia_mat, it was designed to work with gi ala final gathering. phong, blinn and all the other standard shader renders false gi contribution.

from your settings, it looks like you dont know what you do, so my first advice is to read the help. you can see here what the settings mean.
its important to know what the settings do, otherwise you can change them without to get a nice, clean image.

settings that works quite good for example:
automatic mode
view dependent off
rays:300
int:35
presample density:2 (perhaps 3, depends on the shot)
filter size 1

i also had fully dynamic animations where 200 rays were enough, so you have to test this.
a really good combination is also the ibl light and fg because its a direct light and with it you get alot of light that fg can benefit from.
for all types of interior, use protal lights.
a good thing is also the brute force fg mode or exact mode. it gives nice results together with a small falloff distance.

[pdesopo]

Thank you guys for helping out and sorry for replying so late.
I did some other tests, sometimes it works better sometimes not. It's actually something that needs to be tweaked for each scene, but still I can feel confused about how things actually work, even reading the documentation.
Said that, here are a few more renders, the quality is still low but at least I'm getting something:

G_Module-03.jpg

With a bit of PS they're quite usable:

G_Module-02.jpg

G_Module-01_Main.jpg

Unfortunately I cannot open the scene anymore, as if I try SI crashes. Neither the early test I did. I noticed something when last time I saved the scene, an message like "some meshes are not saved correctly", or something like that.

[pdesopo]

Last processed img:

G_Module-03.jpg

[Kzin]

It's actually something that needs to be tweaked for each scene...

this is the normal way. you have to finetune thing like this or sampling, shader in general often from shot to shot.

have you tryed to merge the scene into a new one?

[pdesopo]

this is the normal way. you have to finetune thing like this or sampling, shader in general often from shot to shot.

have you tryed to merge the scene into a new one?

Good tip, it worked out
Thanks Kzin.