View Full Version : Global illumination & FG artifacts

05 May 2002, 01:14 AM
When i try to render an animation of my character using GI or FG i've always the strange artifacts (like flickering of shadows and specular) ,in the final render.

I've try with this Gi settings:

Emitted photons 200000
Accurancy 1000
radius 7

I think that it's only my inexperience that cause this problems



05 May 2002, 01:37 AM
yes! i hate it too!

i just rendered something for about 10 hours with accurasy of 2000 and auto computate and it still flickers a bit.

i really need to learn more about MR sampling to optimise my renderings.

05 May 2002, 02:40 AM
I used to have that problem.

Make sure you have things in your environment for the light to bounce off of and try changing your light intensity. sometimes after a bit of playing around I get it right.
I'm sure someone with a bit more experiance can do a better job of assiting you.:shrug:

05 May 2002, 06:22 PM

A guy on xsi list have solved this problem unchecking Rebuild FG Map & Photon map.

I've make a little test and seems to works fine now


05 May 2002, 06:41 PM
Instead of having a low photon emission with a high accuracy, you should try the opposite: lots of photons (like 1M) and low accuracy (like 300). Also, try drecreasing your radius to something between 0.1 and 2.
For Final Gathering, a setting I like to use is accuracy 3000, min radius 0.01 and max radius 0.1. But on white area it still can give you artifacts.

You should check the numerous tutorials on Global Illumination and Final Gathering on Ed Harriss's website:

Hope this helps
Salutations - Cheers

05 May 2002, 08:24 PM
I've made another test with a ball that moove around a plane......and unchecking Photon map don't works because photons don't follow the sphere.:hmm:

Thank also to Atyss but i already know these tuts and i think that its good only for static images but not for animations

However i'll try to decrease the accuracy and increase the Number of emitted photons.


05 May 2002, 12:34 AM
when you uncheck "photon map > rebuild" photon map is calculated only once (in the first frame) and reused in all the folowing frames. so it's obvious that photons don't folow moving objects ;) unchecking "rebuild" function saves rendering time for scenes where (IMHO) only moving thing is camera.

05 May 2002, 12:26 PM
Actually, xsi did recalculate the photonmap even if u uncheck "rebuild photon map", the difference is that xsi will only caculate information that is absent in the existing map. so in case of animation, the photonmap will get larger and larger as u render ur animation frame after frame coz every time ur camera moves, xsi will add a bit more information to the existing map.

this is according the the xsi2 manual. hope it helps:)

05 May 2002, 05:52 PM
to be honest, i didnt find it all that hard to stop it flickering afterall...
auto computate, 2000 acurasy, 5 image light planes, a floor and a character...

it worked a treat at only about 50 seconds a frame :)

i was suprised.

05 May 2002, 10:06 PM
Also, FG and GI work great if you rayhost your render (assuming you're using more than one machine to render). The rebuild map should only be on if you have moving objects in your scene. If you just have camera animation, than you do not need to rebuild at all. MR will calculate FG and/or GI for each frame even if the rebuild is off but it will not rebuild the whole thing...only what is missing. Either way, rayhost your renders and will get less flickering or even none at all. The rayhost may go slower than rendering individual frames on seperate machines since only machine is generating the mi file but it does give better results.

CGTalk Moderation
01 January 2006, 06:00 AM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.