Ambient occlusion - random black spots ?

Acumen

ok, here i go again
another problem with the ao baking. while i had no problems for the last 10 models whatsoever, suddendly i get these random black spots and have no idea where they are coming from or what to do against it.
my workflo basically always was, to have my ao baking scene with my desired materials and import every model in there. so here's a comparison shot between 2 models i made in the same scene, having applied the same exact materials and didn't change anything on the materials or lights.
there seems to be lighting errors and these (to me) totally random tiny black dots everywhere.
and when i add a ground plane to cast some shadow on the object
the big circular element in the top left corner turns completely black whcih seems totally weird to me.
so does anyone know what i can do to solve this problem and move on ?

renderhjs

I always had that every now and then with Mental Ray so from my experience its definitely because of Mental Ray.
A google search reveals many MR related issues with that:
http://www.google.com/search?rlz=1C1GGLS_enDE291DE338&sourceid=chrome&ie=UTF-8&q=mental+ray+black+dots

some replies of other threads:

Try to increase the Trace depth of finalgathering ( not the same as raytracing )

Problem: Black spots appear in Mental Ray renderings.

Reason: Final Gather does not work with Multi/sub materials with Raytrace reflections that are "FACETED".

Solution: Turn "FACETED" OFF.

I fix the problem by a scale of the entire scene by 0,5 : )

try some of the recipes - see if it helps

my suggestion would be to render in a higher resolution and scale it down in Photoshop - it will less likely produce less annoying black pixels.

Ark

Don't think it's to do with finalgather.

Are you baking from a hi-poly source or applying the AO to the low poly and baking that to a texture?

Bryan Cavett

I've seen this fixed in many different ways and still have no idea which one causes it. Last time someone at work got this was because he was rendering to texture while in an orthographic viewport. As soon as we tried to hit render to texture from a perspective viewport it fixed the problem. I know that if you try to render reflections in an orthogrphic viewport they come out totally wrong so maybe this is something a long those lines. Something with the ways the raytracing works. Then again Ive also seen it fixed by turning off "filter maps" in the render set up window... so who knows

Acumen

ah, sry guys, i always tend to forget to give you more details

i'm not using mental ray, i'm just following this tutorial:
http://www.game-artist.net/forums/vbarticles.php?do=article&articleid=37

- the rendering in higher resolution is something i've already tried before.
scene scaling of 0,5 didn't work either

- Ark, i'm just simple colored materials in max to my lowpoly model and render this to texture as my texture base

- the orthographic/perspective view didn't change anything, neither did "filter maps"

i turned of global supersampling now (forgot why i had it activated already) and manyspots are gone - hooooray !
but still this one cylindrical part just gets unrendered when there's a floor plane underneath it

it's really weird, but thanks to you guys, i know now, that i'm not the only person having this issue and i can just hope, that for the next model, this shall not appear again ! *fingerscrossed*

Acumen

HAHA !! call me nuts, but i figured mine out

so everytime i come here with a problem, Vig tells me to "Reset XForm" and it never did anything good, so i didn't even bother trying this time.
now i was almost done with rebuilding the model and thought "ah what the heck...." aaaaaaand badabaaaam !!! resetted xform and everything works like a charme

so thanks again you guys and in absence, Vig !!

Autocon

Have this same little bug if I leave Global Supersampler Max 2.5 Star on.