TUTORIAL: Dispersion and absorption in specular materials

Forums: TUTORIAL: Dispersion and absorption in specular materials
Post, discuss and share handy resources like textures, models and HDRI maps in this forum.
Forum rules
Please do not post any material that is copyrighted or restricted from public use in any way. OTOY NZ LTD and it's forum members are not liable for any copyright infringements on material in this forum. Please contact us if this is the case and we will remove the material in question.

TUTORIAL: Dispersion and absorption in specular materials

Postby roeland » Tue Aug 30, 2011 1:24 am

roeland Tue Aug 30, 2011 1:24 am
There were two new features added to the specular materials recently:

Dispersion

The IOR (index of refraction) depends on the wavelength of the light entering,
in many materials it is slightly larger for blue light than for red light.
This for example allows to split a beam of white light in a rainbow with a glass prism.

To model the dispersion we use the two-term form of Cauchy's equation.
  • index is used as the A parameter. This input increases or decreases the IOR for
    all wavelengths.
  • dispersion_coefficient_B is used as the B parameter, and controls the amount
    of dispersion. Increasing this parameter increases the dispersion effect, and also slightly
    increases the average IOR over all wavelengths. A value of 0.0 means no dispersion, the
    index input parameter then just gives the IOR for all wavelengths (like in previous versions
    of Octane).

The following image compares a prism with index set to 1.3549, and the B parameter
to 0.0 (left) and 0.02 (right). The beam in the right image is split into colors and slightly
shifted down.
prism comparison.png


Absorption

NOTE: The absorption parameters have been removed from the specular material as of
version 1.0 beta 2.55. You may use the absorption and scale parameters of the new medium
nodes to achieve the same effect.


Absorption means that the material slightly absorbs light while passing through.
The color resulting from this absorption is dependent on the distance light travels through
the material. With increased distance it will get darker, and if the absorption is colored
it will get more saturated.

This is very different from the transmission input, which only controls absorption at
the surface of the material, which is independent of the size of the object.

To specify the absorption two input parameters are used:
  • absorption_color gives the spectrum remaining from white light after traveling
    through the material for a certain distance. Only constant colors are supported
    correctly.
  • depth_of_absorption specifies the aforementioned distance (in meters). The smaller
    this distance, the stronger the absorption will be.


I hope this helps understanding the new parameters,
Roeland
User avatar
roeland
OctaneRender Team
OctaneRender Team
 
Posts: 1741
Joined: Wed Mar 09, 2011 10:09 pm

Re: The new parameters in specular materials

Postby radiant » Tue Aug 30, 2011 3:05 am

radiant Tue Aug 30, 2011 3:05 am
Hey roe land, is it possible if I can grab ahold of the obj file you demonstrated for dispersion.
Win8 Pro 64bit ULT|Intel Core i7 3930K|3.20 GHz|32 GB RAM|GTX 590|UD5 2011 socket||2x TB HD||Master Cooler HAF X||Blender 2.6||Maya 2012||Octane|
User avatar
radiant
Licensed Customer
Licensed Customer
 
Posts: 699
Joined: Mon Apr 05, 2010 12:00 pm
Location: Adelaide, Australia

Re: The new parameters in specular materials

Postby roeland » Tue Aug 30, 2011 5:42 am

roeland Tue Aug 30, 2011 5:42 am
Yes, this is the obj and mtl file.

--
Roeland
Attachments
prism.zip
(670 Bytes) Downloaded 666 times
User avatar
roeland
OctaneRender Team
OctaneRender Team
 
Posts: 1741
Joined: Wed Mar 09, 2011 10:09 pm

Re: The new parameters in specular materials

Postby radiant » Tue Aug 30, 2011 10:53 am

radiant Tue Aug 30, 2011 10:53 am
cheers roeland, doing some major testing.

Question:

Is there any greater angle of the triangle (facing the light) which shows the out coming caustics at its best?
Win8 Pro 64bit ULT|Intel Core i7 3930K|3.20 GHz|32 GB RAM|GTX 590|UD5 2011 socket||2x TB HD||Master Cooler HAF X||Blender 2.6||Maya 2012||Octane|
User avatar
radiant
Licensed Customer
Licensed Customer
 
Posts: 699
Joined: Mon Apr 05, 2010 12:00 pm
Location: Adelaide, Australia

Re: The new parameters in specular materials

Postby roeland » Wed Aug 31, 2011 12:09 am

roeland Wed Aug 31, 2011 12:09 am
I don't know the optimal angles for the triangle. One thing that will definitely improve the brightness of the caustic is tilting upwards the plane behind the prism, so the beam hits it at a less acute angle.

--
Roeland
User avatar
roeland
OctaneRender Team
OctaneRender Team
 
Posts: 1741
Joined: Wed Mar 09, 2011 10:09 pm

Re: The new parameters in specular materials

Postby colorlabs » Wed Aug 31, 2011 11:24 pm

colorlabs Wed Aug 31, 2011 11:24 pm
Thanks for this. I have a question - as Octane is a "physically based renderer," I must ask - are there any specular materials in the REAL world that do NOT absorb light? i.e., is there any reason to use transmission instead of absorption, aside from the fact that it might require less tweaking for simple models or models with consistent thickness?
Mac OS X 10.8.0 | ASUS GTX 580 1.5GB | MSI GTX 470 | ATI Radeon 6870 | Core i7 2.9Ghz | 16GB
colorlabs
Licensed Customer
Licensed Customer
 
Posts: 209
Joined: Sun Aug 08, 2010 2:53 pm

Re: TUTORIAL: Dispersion and absorption in specular materials

Postby fibernaut » Thu Mar 05, 2015 1:14 pm

fibernaut Thu Mar 05, 2015 1:14 pm
Hi Roeland

is it possible to bring this thread back to life with reference to the newest Octane version with all its parameters, especially the Absorption Medium? Can you reproduce this example scene for Octane 2.x?
I am trying to get a similar result but it looks quiet modest. :)

Thank you very much in advance!
Win 8.1 64 | 2x GTX1080Ti 1x GTX 980Ti| 2x Xeon E5 2650v2 | Supermicro X9DAi | 64 GB ECC Reg.
Win 7 64 |4x GTX780Ti | i7 2600K | AsRock Z68 Extreme3 | 32 GB
Win 8.1 64 | 4x GTX780 2x GTX780Ti 1x GTX980Ti| I7 3770 K | 16 GB
fibernaut
Licensed Customer
Licensed Customer
 
Posts: 57
Joined: Mon Jun 03, 2013 8:55 am

Re: TUTORIAL: Dispersion and absorption in specular materials

Postby User21 » Wed Nov 09, 2016 12:18 am

User21 Wed Nov 09, 2016 12:18 am
I am also interested in seeing if this can recreated within the current C4D build.
User21
 
Posts: 1
Joined: Wed Nov 09, 2016 12:16 am

Return to Resources and Sharing


Who is online

Users browsing this forum: No registered users and 4 guests

Mon Oct 21, 2019 3:23 pm [ UTC ]