www.BinaryAlchemy.de :: View topic - BA Volume Cloud detail flicker question
 SearchSearch   RegisterRegister  ProfileProfile   UsergroupsUsergroups   Log inLog in 
If you create a new post, please use a topic that describes your problem
Documento sin título
 
BA Volume Cloud detail flicker question

 
Post new topic   Reply to topic    www.BinaryAlchemy.de Forum Index -> Shader Questions / Comments
View previous topic :: View next topic  
Author Message

Pitcher



Joined: 23 Mar 2005
Posts: 114
Location/Company/Country: Gimmick VFX/Denmark

PostPosted: Wed Apr 01, 2009 8:55 am    Post subject: BA Volume Cloud detail flicker question Reply with quote

Hi Holger

I am using BA Volume V2.1 Volume Cloud on spherical particles to create a cloud layer. Particles are rotating slowly and the Fractal 4D turbulence is animated over time, slowly, to cretae some development in the cloudlayer. Camera is stationary. I get some flicker in edge details, which look like density popping on cloud detail edges - not shadow flicker, so upping the no of Look up Table Cells probably will not help. I am using 7 density texture samples per cell.

Is this a marching issue or how do I go about fixing it?

best
Morten Bartholdy
_________________
Morten Bartholdy
Colorshop VFX
Denmark
Back to top
View user's profile Send private message Send e-mail

schoenberger
Site Admin


Joined: 02 Mar 2005
Posts: 3786

PostPosted: Wed Apr 01, 2009 12:01 pm    Post subject: Reply with quote

There is a setting on the marching tab to influence the limits of the density limit of the lookup cells.

"Call input textures if density is between".
Lower the min value.
This should only have an effect if you have very thin lines of density.
_________________
Holger Schönberger
Binary Alchemy - digital materialization
Back to top
View user's profile Send private message Send e-mail

Pitcher



Joined: 23 Mar 2005
Posts: 114
Location/Company/Country: Gimmick VFX/Denmark

PostPosted: Thu Apr 02, 2009 12:04 pm    Post subject: Reply with quote

So I lowered the value from -0.035 to -0.095 and rendertime went from 7.5 min/frame to 19.75 min/frame - it seems it fixes the flicker, but it looks like it is a thin line between rendertime cost and quality. Based on your experience would you say going to -0.095 is way too low for slow moving cloud stuff?
_________________
Morten Bartholdy
Colorshop VFX
Denmark
Back to top
View user's profile Send private message Send e-mail

Pitcher



Joined: 23 Mar 2005
Posts: 114
Location/Company/Country: Gimmick VFX/Denmark

PostPosted: Thu Apr 02, 2009 12:06 pm    Post subject: Reply with quote

BTW if it uses lookup cells beyond these density limits, would it help to increase the number of cells, so the flicker would become less noticeable?
_________________
Morten Bartholdy
Colorshop VFX
Denmark
Back to top
View user's profile Send private message Send e-mail

schoenberger
Site Admin


Joined: 02 Mar 2005
Posts: 3786

PostPosted: Thu Apr 02, 2009 12:21 pm    Post subject: Reply with quote

I would have to see a picture of the fractal detail, perhaps with cell size painted in.
Cells are not used, if almost no density is found.
As you said, you are using 7 samples per cell.
These 7 samples are averaged and then decided if the input texture is used or not.
If not, the cell is rendered empty.

It it it used, it calls the input texture a lot of times during rendering.


So in your case:
The fractal detail is that small that it happens to fit in the space between the 7 samples in a cell.
This usally only happens if the fractal detail size has a width of 1/5 of a cell.
Reducing the cell size should help then.
_________________
Holger Schönberger
Binary Alchemy - digital materialization
Back to top
View user's profile Send private message Send e-mail

Pitcher



Joined: 23 Mar 2005
Posts: 114
Location/Company/Country: Gimmick VFX/Denmark

PostPosted: Thu Apr 02, 2009 1:24 pm    Post subject: Reply with quote

I will do some further testing - if it keeps giving me trouble, perhaps I could put a scene on my ftp for you so you could perhaps take a look see if one or more of my settings are totally off.

Regarding rendertime it looks to me like raising the number of cells and lowering the minimum density value both contribute to longer rendertimes, presumably because I get a lot more texture lookups, no!?

What would be the best method to work in order to avoid density flickering like this would you say - cranking parameters up a notch at a time and render a subregion for speed, or is there a way to turn the bells and whistle off when testing for this, and when good parameters are found, let the renderfarm have its time?
_________________
Morten Bartholdy
Colorshop VFX
Denmark
Back to top
View user's profile Send private message Send e-mail

schoenberger
Site Admin


Joined: 02 Mar 2005
Posts: 3786

PostPosted: Thu Apr 02, 2009 1:37 pm    Post subject: Reply with quote

It also depends on how hard the contrast on the edges is.
If the falloff is smoother, then your flicker is probably gone.
_________________
Holger Schönberger
Binary Alchemy - digital materialization
Back to top
View user's profile Send private message Send e-mail

Pitcher



Joined: 23 Mar 2005
Posts: 114
Location/Company/Country: Gimmick VFX/Denmark

PostPosted: Thu Apr 02, 2009 2:12 pm    Post subject: Reply with quote

I will try that too and cross fingers for tonights render.
_________________
Morten Bartholdy
Colorshop VFX
Denmark
Back to top
View user's profile Send private message Send e-mail

Pitcher



Joined: 23 Mar 2005
Posts: 114
Location/Company/Country: Gimmick VFX/Denmark

PostPosted: Tue Apr 14, 2009 10:11 am    Post subject: Reply with quote

Hi Holger

I tried lowering the minimum value to -0.095 and increased the Use table if alpha to 0.9, plus lowered the contrast some. It reduced the popping but some remains - see movie here:

http://colorshopvfx.dk/XSI/BA/Volume_CloudPopping_01.mov - 1MB

In case you have time and want to take a closer look you can grab the scene here:

http://colorshopvfx.dk/XSI/BA/SC35_CloudFloor_Large_P_03.rar - 1 MB

I am going to try lowering the minimum value further, but would you say that is the way to go or is there something else I should look out for?

Thanks!
_________________
Morten Bartholdy
Colorshop VFX
Denmark
Back to top
View user's profile Send private message Send e-mail

schoenberger
Site Admin


Joined: 02 Mar 2005
Posts: 3786

PostPosted: Tue Apr 14, 2009 2:09 pm    Post subject: Reply with quote

Hi

The cloud detail structure does not seem to be that fine that the sampling misses the input.

Perhaps the values you pipe from the input shader into the volume cloud are very very low.
Do you know wha range your input has in that area?

Try to add a math_scalar before the volume density input and multiply it by 10.
(and then reduce the denisty in the volume by 10)
_________________
Holger Schönberger
Binary Alchemy - digital materialization
Back to top
View user's profile Send private message Send e-mail

Pitcher



Joined: 23 Mar 2005
Posts: 114
Location/Company/Country: Gimmick VFX/Denmark

PostPosted: Wed Apr 15, 2009 9:40 am    Post subject: Reply with quote

Holger, I tried your multiplication suggestion which actually seemed to makes the popping a bit worse.

I don't know what the values I pipe in are - they come from the PT_metaball which is multiplied by a Fractal4d._scl. You can check the values in the scene - it is quite small - less than a MB:

I will try lowering the Min volume density value even more, but do you have other suggestions? I sort of have a feeling it is a particular combination of settings that are causing this, and even though I have used the shader a fair bit I have never run into this problem before.

http://colorshopvfx.dk/XSI/BA/SC35_CloudFloor_Large_P_03.rar
_________________
Morten Bartholdy
Colorshop VFX
Denmark
Back to top
View user's profile Send private message Send e-mail
Display posts from previous:   
Post new topic   Reply to topic    www.BinaryAlchemy.de Forum Index -> Shader Questions / Comments All times are GMT + 1 Hour
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
 
Documento sin título
 



Powered by phpBB © 2001, 2002 phpBB Group



Number of shameful bots caught by Anti-Spam ACP: 1667