Artifacts with … GI?

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  08 August 2006
Artifacts with … GI?

I really donīt know the reason. Iīm focused in architectural visualization.
When I render an animation, I get "no reason artifacts" between one frame and the next.
Normally all is fine but, sometimes, a spot apears in some frames.
The first thoght about it was a modelling trouble…No way. Using other cameras looking at the same area of, in this case bulding, all was rendered perfectly.
The second thought was something in relation with the layers of glass but… This trouble also appears in areas without reflections or transparency so…
My third thought was something in relation with GI.
Itīs very frustated get a large animation-render time and, when finished, some frames are brong.
Any idea could be apreciated.

This are my GI set:
Primary>100
Secondary>0
Intensity>2
Gi Sampling>4x4
Bounces>0

Excluding set>glass of the building.

Thanks in advance !
 
  08 August 2006
Hi,
Have you tried increasing the tessalation in the GI trouble areas?
I've found that this helps in most of my GI animation renders when I get artifacts.
 
  08 August 2006
Not yet but Iīll do asap 1

Thanks in advance !

Iīll tell you the result.
 
  08 August 2006
For starters, your primary ray count is very low for an animation, but then I don't know what you are rendering....

The Manual has some great tips on getting rid of these 'splotches'.
First, try increasing the GI sampling setting (to 4x4) the default is 8x8.
Then try increasing the colour tolerance to something like 10.
Still no joy?
Then increase the primary rays (try 200).

Adding more dirt maps to your materials also helps reduce the visibility of these artefacts.

That's a start anyway!
Ian

PS. There are lots of threads in this forum about GI settings for animation, a search might turn up something useful!
 
  08 August 2006
Hi, Gayata
Originally Posted by GAYATA: I really donīt know the reason. Iīm focused in architectural visualization.
When I render an animation, I get "no reason artifacts" between one frame and the next.
Normally all is fine but, sometimes, a spot apears in some frames.
The first thoght about it was a modelling trouble…No way. Using other cameras looking at the same area of, in this case bulding, all was rendered perfectly.
The second thought was something in relation with the layers of glass but… This trouble also appears in areas without reflections or transparency so…
My third thought was something in relation with GI.
Itīs very frustated get a large animation-render time and, when finished, some frames are brong.
Any idea could be apreciated.

This are my GI set:
Primary>100
Secondary>0
Intensity>2
Gi Sampling>4x4
Bounces>0

Excluding set>glass of the building.


1) Read what Ian wrote

2) 100 rays = draft sketch, animation requires 200 and more rays

3) Intensity = 2 should be "confirmed" with more rays (more inensity - more noise)

So, summary: increase rays count step by step and see "tendency". If it's not a standard problem (more rays couldn't help) then minimize your prj, archive and upload it
 
  08 August 2006
First of all thanks a lot !

I know. Many factors, different scenes with his own geometry peculiarity.

Anyway, Iīm trying with all of these variables.

Other related (more or less) question. Before,I used to work with the topic 3 lights. Now, with GI, whatīs you recommendation about the lights? :

1. Main :NORMAL
2. Second : Secondary or ignore ?
3. Third : Secondary or ignore ?

…going to test !

Thanks again !
 
  08 August 2006
yuk! three point lighting

I'm not a fan of traditional three point lighting, it isn't very imaginative.

I tend to use (though not as a rule):

Sun light (yellow hue)
GI Sky light (yellow hue)
Sky dome (blue sky map reflection object with luminance, with bounce lighting this will also help illuminate your scene).

Then, and I know this is controversial so beware:

I use a parallel light lightrig on a very low intensity with GI mode set to secondary. This is, primarily, to help with the architectural reflections.

Also there is the option of adding a 'highlight only' sun. If I have a lot of glass in a scene that can really be a help in getting the 'look' I'm after, and then sometimes I use a 'shadow killer' sunlight as well, though, not often.
Ian

Last edited by halfworld : 08 August 2006 at 01:00 PM.
 
  08 August 2006
Hi, Gayata
Originally Posted by GAYATA: Other related (more or less) question. Before,I used to work with the topic 3 lights. Now, with GI, whatīs you recommendation about the lights? :

1. Main :NORMAL
2. Second : Secondary or ignore ?
3. Third : Secondary or ignore ?
The "secondary" (GI Window) defines how many rays should be cast for secondary points, i.e. points are shaded for RT reflections/refractions. If you don't use these features, leave "secondary" = 0 and don't worry.

The popup "GI Mode" (Light Window) allows to foolish GI. Start from "normal" for all lights and see. Imagine a scene is "too dark" for your taste. One way is to increase sky and/or energy bias intensity. However, it can raise up new problems (for example sky inensity 2 can be more noised). There is a way to cheat: add a light (typically without shadow) and set "GI mode" to "exclusive". Activate "reverse illumination" in GI Window. Now the light is visible for GI reverse illumination only that counts it and thus produces more lighting.

Keep in mind: this trick is "for artistic purposes only", it has no any physical foundation.

The "secondary" choice (GI mode popup) is a similar trick but for secondary points only. It can be very helpful if you use GI together with RT reflections/refractions

Last edited by Igors : 08 August 2006 at 01:06 PM.
 
  08 August 2006
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