absorption and scattering coefficients for liquids

General questions about Indigo, the scene format, rendering etc...
Phil
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Post by Phil » Thu Jan 18, 2007 8:06 am

:shock: :shock: :shock:

hi, your render looks super!
I am still not able to get good results :cry:

Regards, Phil

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CTZn
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Post by CTZn » Thu Jan 18, 2007 8:31 am

Roxx Hard ZomB !!!

You will find about polarisation at Nick's blog:

http://www.indigorenderer.com/blog/?p=36

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Camox
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Post by Camox » Fri Jan 19, 2007 1:51 am

:shock: wow, that looks so real !

Fantastic !!! :D

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OnoSendai
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Post by OnoSendai » Sat Jan 20, 2007 4:55 pm

ZomB:
That's a great wine glass model (the left one).
Is it modeled according to the glass test thread specs: http://www.indigorenderer.com/joomla/fo ... .php?t=637.

If so, can u make the model public? Then I'll make a standard test scene with it. (or you could do that)

Either way, if you send me the model, i'll chuck it up for download.

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CTZn
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Post by CTZn » Sat Jan 20, 2007 5:23 pm

There's something weird, tho, certainly that's correct but looks weird: the way the table reflects in the glass is not uniform, albeit the table itself is uniformly lit.

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Zom-B
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Post by Zom-B » Sun Jan 21, 2007 9:10 am

OnoSendai wrote:ZomB:
That's a great wine glass model (the left one).
Is it modeled according to the glass test thread specs: http://www.indigorenderer.com/joomla/fo ... .php?t=637.

If so, can u make the model public? Then I'll make a standard test scene with it. (or you could do that)

Either way, if you send me the model, i'll chuck it up for download.
Yes, its modeled according to your advice in the glass test scene,
and yes, I would love to share this work!!!
would you like that I reduce the scene to no texture and no HDRI with only one glass, to keep focus on this "glass -fluid situation" and keep file size low?!
(but the HDR lightning does a lot of magic to the glass, 1.1MB)

I also got a question about the values of the Henyey-Greenstein Parameter, the value for Merlot for example is 0.974 − − does this mean I have to use g_spectrum of 0.974 0 0 or only one number 0.974 ???


CTZ wrote:There's something weird, tho, certainly that's correct but looks weird: the way the table reflects in the glass is not uniform, albeit the table itself is uniformly lit.
good Eyes you got boy!
I just rendered 3 Beer Spheres over night, using new 0.7t2 build... check em out:

Image

the lightsource reflection fades out on the right side on the top, and the ground reflection fades aout on the lower leftside
(Scene is a perfect frontview, with lightsource, sphere and camera on X = 0)

this problem is caused by the polarisation enabled... setting this to false, the reflections look like they should!

Image
polygonmanufaktur.de

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OnoSendai
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Post by OnoSendai » Sun Jan 21, 2007 5:58 pm

MMmmnnn beer spheres :)

For the Henyey-Greenstein g parameter,
Note that in the paper it has a g value for each of R, G, B.
so, for milk(lowfat), use this:

Code: Select all

<g_spectrum>
  <rgb>
     <rgb>
       0.932 0.902 0.859
    </rgb>
  </rgb>
</g_spectrum>
About the scene... Perhaps u could set up a standard test scene with the one glass and the HDR.
Just on a plain white table/surface (or a little textured, needs to be mainly white tho)

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dogfin
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Post by dogfin » Sun Jan 21, 2007 6:10 pm

Somethings up with the budwiser sphere...do they make an ale now? 8)

Ryan -
Image

8bstudio
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Post by 8bstudio » Mon Jan 22, 2007 9:55 pm

ZomB, very good your tests! I'm not be able to obtain same results... :(

Here new table with coefficients:
http://www.8bstudio.com/bonus/scattering-new.pdf

Soon I'll try v0.7t2 me too!! Bye and great job Ono!!!

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Zom-B
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Post by Zom-B » Mon Jan 22, 2007 10:29 pm

8bstudio wrote:ZomB, very good your tests! I'm not be able to obtain same results... :(

Here new table with coefficients:
http://www.8bstudio.com/bonus/scattering-new.pdf

Soon I'll try v0.7t2 me too!! Bye and great job Ono!!!
Thanks dude for the updated Table... very Handy!!!
I just realized, that I used the Henyey-Greenstein Parameter wrong (for the beer-Spheres)!!!

I used (wrong):
<phase_function>
<henyey_greenstein>
<g_spectrum>
<uniform>
<value>0.917 0.956 0.982</value>
</uniform>

</g_spectrum>
</henyey_greenstein>
</phase_function>
instead of (right):
<phase_function>
<henyey_greenstein>
<g_spectrum>
<rgb>
<rgb>0.917 0.956 0.982</rgb>
</rgb>

</g_spectrum>
</henyey_greenstein>
</phase_function>
So I have to render the beer again...
polygonmanufaktur.de

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OnoSendai
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Post by OnoSendai » Mon Jan 22, 2007 10:32 pm

Hmmm, your wrong example really shouldn't have parsed :)

Phil
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Post by Phil » Thu Jan 25, 2007 7:38 am

Hi all,

I am still testing some effects on a glass of wine.

This a first interesting result, but I am still not satisfyed :(

Image

The wine is here a white zinfandel:

Code: Select all

<ior>1.33</ior>
		<cauchy_b_coeff>0.0</cauchy_b_coeff>
		<absorption_coefficient_spectrum>
			<uniform>0.0</uniform>
			<rgb>
				<rgb>1.7320 2.3220 2.8470</rgb>
			</rgb>
		</absorption_coefficient_spectrum>
		<precedence>10</precedence>
		<subsurface_scattering>
			<scattering_coefficient_spectrum>
				<rgb>
					<rgb>0.0310 0.048 0.066</rgb>
				</rgb>
				
			</scattering_coefficient_spectrum>
			<phase_function>
				<uniform/>
			</phase_function>
		</subsurface_scattering>
The glass is not uniform here, I modelized some extra geometry like:

- a fissure which is 0,03 mm width
- some extra waves or ripples on the inside wall of the glass

I modelized some imperfections and hope I could see these imperfections in the shadow and in the caustics.
But I do not really see such effects right now, perhaps should I let Indigo render longer.


The environment is a black ambient world with 3 mesh emitters.
The plane is standard mesh plane in Blender, so the dimensions are 2x2 meters
Rendering time is now more than 22 hours (Athlon 64 3800+)

In the logs, I see sometimes 50 or 60 PANIC: tryed to exit from medium when not inside it.
betwenn saving the image, and somtimes I only see 2 or 4 times this message between saving the image.

Some questions:

1)- Should I wait longer before seein the results in the shadow and caustics?

2)- Should I change the position and / or brightness of the mesh emitters?

3)- Should I modelize a box around all the objects containing air?
(could the precedence here be a problem?)

4)- Is there a problem with the units in blender or in Indigo or in my obj import?
I mean: The plane is is 2 meters in dimension, so the glass seems to be correct.
But when I appy this for a merlot wine:
Absorption:
7.5860 16.4290 19.1930
Scattering
0.053 0.0 0.0

I only see a very transperent red wine, not the dark red as expected.

5)- Did some of you made some similar experience?

6)- Is it possible to realsie such a fissure in Blender (0.03 mm) with boolean operations?

Thanks in advance.

Regards, Phil

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Zom-B
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Post by Zom-B » Thu Jan 25, 2007 8:09 am

Hey Phil...

Try a cauchy_b_coeff of 0.003 for water-like liquids.
in your absorption_coefficient_spectrum you first define a uniform 0 valua AND then a RGB value... only one of both should be inside this!!!

Also try the g Parameters inside the phase_function (07t2)just like:

Code: Select all

<phase_function>
            <henyey_greenstein>
               <g_spectrum>
                  <rgb>
                      <rgb>R G B</rgb>
                  </rgb>
               </g_spectrum>
            </henyey_greenstein> 
         </phase_function>
The RGB values for your wine could be directly taken from the paper!

SSS Materials are (very) dependent of Model size... if your merlot is to transparent, try to raise the size of your model...

Sorry that I can't answer all questions :oops:
polygonmanufaktur.de

Phil
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Post by Phil » Thu Jan 25, 2007 8:49 am

hi ZomB,

I tryed cauchy_b_coeff (but this eeems to be so slow that I stpped after some hours)
SSS Materials are (very) dependent of Model size... if your merlot is to transparent, try to raise the size of your model...
I played a lot with the size of the material, this is why I think there is somewhere a unit problem
Sorry that I can't answer all questions Embarassed
Do not worry, better some answers as nothing, my computers can only test 1 or 2 parameters per day (or week) :lol:

I will try all other parameters, and remarks:

Thanks again ZomB :D

Regards, Phil

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manitwo
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Post by manitwo » Thu Jan 25, 2007 10:25 am

As Zom-B already pointed out, this might be the problem:

<absorption_coefficient_spectrum>
<uniform>0.0</uniform>
<rgb>
<rgb>1.7320 2.3220 2.8470</rgb>
</rgb>
</absorption_coefficient_spectrum>

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