Refractive material question

[subpixel]

Hey,
While working on material implementation, I'm wondering is there a physical material which would only refract light without reflecting it (like specular does)? I mean scenarios with IOR > 1. Any idea?

Thanks,

Note: This thread is reposted from Max Forum: http://www.indigorenderer.com/forum/vie ... f=9&t=9964

[lycium]

Not possible I think, in real life or Indigo

[Godzilla]

in real life

Gasses?

[lycium]

Hmm, I suppose you could define a medium with scattering (reflection) coefficient zero.

[subpixel]

And is (how is) it doable with Indigo?
Excuse my ignorance.
Regards,

[lycium]

Hmm, I suppose you define a medium with scattering_coefficient_spectrum as a uniform 0, and with the absorption_coefficient_spectrum as uniform 0 too.

Adapted from the Technical Ref Manual:

Code: Select all

<medium>
<name>scattering_medium</name>
<ior>1.5</ior>
<cauchy_b_coeff>0.0</cauchy_b_coeff>
<absorption_coefficient_spectrum>
<uniform><value>0</value></uniform>
</absorption_coefficient_spectrum>
<subsurface_scattering>
<scattering_coefficient_spectrum>
<uniform><value>10</value></uniform>
</scattering_coefficient_spectrum>
<phase_function><uniform/></phase_function>
</subsurface_scattering>
</medium>

Once again I'm amazed at how onto it you are Godzilla

[subpixel]

Thanks a lot, I'll give it a try.
Thanks,

[CTZn]

Still, reflection rays won't be killed and would contribute to the scene ?

Agreed, it's not realistic. But in most (ideal) cases lenses are of interest only as light benders. They are not thought to be visible by themselves through (total internal) reflection. Killing reflection rays might justify the material, performances wise, and might allow for much more fun in ceilings.

It might add to Indigo Indeed, it could just be an option to the existing specular material.

[galinette]

Scattering will not prevent the reflection. Not working here...


Actually, this is physically not possible on a simple air/material interface. Refraction & reflection are part of the same phenomenon.
However, you can do it the following ways:
- By using a refractive index gradient, smoothly transitionning from air to material. This is what happens in mirages
- By using an antireflection coating on the material. This will not cancel totally reflection, but will reduce it somewhat.


Also not possible in Indigo. However, it's technically possible to implement this in unbiased renderers.

You can probably do an approximation of the index gradient, by making many parallel surfaces and applying them materials with progressive refractive index transition. However, this may takes ages to render.

Etienne

[subpixel]

To lycium: I tried your solution, however with no luck, specular was still there and refraction rays got fuzzy (if you know what I mean) Thanks though.

To galinette: I agree with you. I guessed it's not physically possible (in normal conditions), I just wanted to hear it from someone else Thanks.