dichroic glass

hva · Tue Mar 17, 2009 5:28 am

I'm modeling a new building we are designing. Modeling in Blender and going to da final render with Indigo.
It's supposed to have a glass skin treated with a dichroic thin film or coating.
I though maybe indigo would be able to render this kind of material somehow, but I don't really know how. could someone help me pointing me in the right direction?

hva · Tue Mar 17, 2009 8:53 pm

I forgot to mention that I used to fake the effect of a dichroic glass in blender rather easily through the use of a magic procedural texture. Of course this can't be the way in Indigo for qhat i can see.

CTZn · Tue Mar 17, 2009 9:43 pm

What was the magic of the procedural texture hva ? Based on light or camera angles, or world orientation ? These informations are not accessible via isl (apart maybe the later), they must be taken ("baked" ?) from the host app/exporter to be aknowledged by the Indigo Shading Language; this is an advanced topic, exporter-specific until isl allow such accesses.

Questions regarding your scene:

Do you expect transparency from your dichroic glass ? If yes, how close/accurate ? Or reflections would be enough ?

The most accurate approximation I can imagine right now is a glass with different colors for absorbtion and sub-surface scattering. Scatter should be of a tight spread angle... Either what you might be able to bake the procedural texture and use it on a blended phong, as specular_reflectivity...

all theorical

CTZn · Wed Mar 18, 2009 2:34 am

Something around those lines:

Code:

<medium>
   <name>dichrolike_medium</name>
   <precedence>6</precedence>
   <basic>
      <ior>1.393849969</ior>
      <cauchy_b_coeff>0</cauchy_b_coeff>
      <absorption_coefficient_spectrum>
            <rgb>
               <rgb>0.0420953331 0.010 0.03045000076</rgb>
               <gamma>2.200000048</gamma>
            </rgb>
      </absorption_coefficient_spectrum>
      <subsurface_scattering>
         <scattering_coefficient_spectrum>
            <rgb>
               <rgb>3.195000076 16 4.097499847</rgb>
               <gamma>2.200000048</gamma>
            </rgb>
         </scattering_coefficient_spectrum>
         <phase_function>
            <henyey_greenstein>
               <g_spectrum>
            <rgb>
               <rgb>1 0 1</rgb>
               <gamma>1</gamma>
            </rgb>
               </g_spectrum>
            </henyey_greenstein>
         </phase_function>
      </subsurface_scattering>
   </basic>
</medium>

<material>
   <name>previewmaterial</name>
   <specular>
      <transparent>true</transparent>
      <internal_medium_name>dicrolike_medium</internal_medium_name>
   </specular>
</material>

Don't use that material if it's not for real glassery or jewelry, not that it correspond to an existing material but it will not be efficient for exterior shots I fear.

Again it's an approximation, colours are split not based on their wavelenghts but on their nature, absorbed/scattered. Though, the phase_function parameter will dispatch scattering based on wavelenghts (kind of), you may want to experiment with that one. Also you may want to divide scale-dependent parameters by 10 or 100 in that code. Finally, colors are not balanced.

An image with that material is cooking, will post.

cpfresh · Wed Mar 18, 2009 3:52 am

can't wait to see this material render ...

CTZn · Wed Mar 18, 2009 4:10 am

Eat it crude then :lol:

(edit: it's better cooked now)

You can see the effect of the phase function: scattering red and blue components are propagating almost straight inside the medium, while green has a razing scattering angle. Of course both emiters are of plain white emission.

Edit: directly inspired by http://www.indigorenderer.com/joomla/co ... temId=6578

PS: Unlike what I formerly stated, since this shader heavily relies on phase function it can be called "polychroic" (can it actually ?), dichroism is effectively reached because R and B components have the same phase param; It's not simply discriminating between (non) absorbed light and scattered light.

Kram1032 · Wed Mar 18, 2009 6:44 am

pretty nice test

CTZn · Wed Mar 18, 2009 7:55 am

I'm currently tweaking the material, depending on results I may upload it in the matDB.

Update:

Code:

<?xml version="1.0" encoding="utf-8"?>

<scenedata>
   <medium>
      <name>dichro_medium</name>
      <precedence>6</precedence>
      <basic>
         <ior>1.393849969</ior>
         <cauchy_b_coeff>0</cauchy_b_coeff>
         <absorption_coefficient_spectrum>
               <rgb>
                  <rgb>6 3.5 3</rgb>
                  <gamma>2.2</gamma>
               </rgb>
         </absorption_coefficient_spectrum>
         <subsurface_scattering>
            <scattering_coefficient_spectrum>
               <rgb>
                  <rgb>11 6 14</rgb>
                  <gamma>2.200000048</gamma>
               </rgb>
            </scattering_coefficient_spectrum>
            <phase_function>
               <henyey_greenstein>
                  <g_spectrum>
                     <peak>
                        <peak_min>485</peak_min>
                        <peak_width>80</peak_width>
                        <base_value>-0.065</base_value>
                        <peak_value>0.72</peak_value>
                     </peak>
                  </g_spectrum>
               </henyey_greenstein>
            </phase_function>
         </subsurface_scattering>
      </basic>
   </medium>
   
   <material>
      <name>previewmaterial</name>
      <specular>
         <transparent>true</transparent>
         <internal_medium_name>dichro_medium</internal_medium_name>
      </specular>
   </material>
</scenedata>

Nearly final, you can save it as an igm file.

Jambert · Wed Mar 18, 2009 7:07 pm

Simply Great

cpfresh · Wed Mar 18, 2009 7:08 pm

CTZn
very very cool!

CTZn · Wed Mar 18, 2009 8:57 pm

Thanks a lot, Jambert and cpfresh !

I'll look for references now and will try to get a final material. hva, such references would have come in handy

Perhaps I'll explain what's going on with that peak spectrum then.

How helpfull do you see these materials hva ?

CTZn · Wed Mar 18, 2009 10:02 pm

Some investigations:

from http://www.lasercommunity.com/lc_view_p ... php?aid=17 about lasers:

Quote:

If you really want a beamsplitter, they are available online. Watch out, as some are polarizing (reflect/refract based on the angle of polarization of the laser) while others are dichroic (reflect/refract based on wavelength of light).

wich pointed me to perhaps use tabulated data for phase function, along with another one for ior [edit: scratch the later]...

found this: J-band Dichroic Mirror Transmission Data Table - [link to main page]

Note that the page also contains interesting atmospherical data.

CTZn · Thu Mar 19, 2009 5:23 am

Final, or close; I'm not sure about absorbtion:

Code:

<?xml version="1.0" encoding="utf-8"?>

<scenedata>
   <medium>
      <name>dichroic_glass_A_medium</name>
      <precedence>6</precedence>
      <basic>
         <ior>1.39</ior>
         <cauchy_b_coeff>0.0018</cauchy_b_coeff>
         <absorption_coefficient_spectrum>
               <rgb>
                  <rgb>1.27 2.45 1.8</rgb>
                  <gamma>2.2</gamma>
               </rgb>
         </absorption_coefficient_spectrum>
         <subsurface_scattering>
            <scattering_coefficient_spectrum>
               <rgb>
                  <rgb>4.4 3.2 4.8</rgb>
                  <gamma>2.200000048</gamma>
               </rgb>
            </scattering_coefficient_spectrum>
            <phase_function>
               <henyey_greenstein>
                  <g_spectrum>
                  
                     <!--peak>
                        <peak_min>480</peak_min>
                        <peak_width>70</peak_width>
                        <base_value>-0.065</base_value>
                        <peak_value>0.72</peak_value>
                     </peak-->
                     
                     <regular_tabulated>
                        <start_wavelength>0.4E-06</start_wavelength>
                        <end_wavelength>0.7E-06</end_wavelength>
                        <num_values>6</num_values>
                        <values>
                        -0.975 -0.8 -0.6 0.6 0.8 0.975
                        </values>
                     </regular_tabulated>
                     
                  </g_spectrum>
               </henyey_greenstein>
            </phase_function>
         </subsurface_scattering>
      </basic>
   </medium>
   
   <material>
      <name>previewmaterial</name>
      <specular>
         <transparent>true</transparent>
         <internal_medium_name>dichroic_glass_A_medium</internal_medium_name>
      </specular>
   </material>
</scenedata>

Some more tweakings and I upload it.

PureSpider · Thu Mar 19, 2009 6:39 am

UT voice from somewhere: TRI-TRI-TRIPPLE POST!

Really like what you created here

Keep it on and finish it

CTZn · Thu Mar 19, 2009 1:34 pm

If that wasn't with you I would have beaten my own record right now :twisted:

Eeew, I'm tweaking, documenting myself, rendering, pruning renders, learning, eventually spreading knowledge...

Basically reporting, no

?

Note: All these materials should greatly benefit from a very subtle bump mapping, smooth wavy style. If you can displace that, that would be even better. Perfect flat surfaces are so boring !

Code:

<?xml version="1.0" encoding="utf-8"?>

<scenedata>
   <medium>
      <name>dichroic_glass_B_medium</name>
      <precedence>6</precedence>
      <basic>
         <ior>1.48357</ior>
         <cauchy_b_coeff>0.00072487</cauchy_b_coeff>
         <absorption_coefficient_spectrum>
                     <regular_tabulated>
                        <start_wavelength>0.4E-06</start_wavelength>         <!-- from the beginning of the visible spectrum -->
                        <end_wavelength>0.7E-06</end_wavelength>            <!-- to its end -->
                        <num_values>20</num_values>                  <!-- get 20 samples -->
                        <values>                                 <!-- 5x4 -->
                           0 0.01 0.03 0.003 0.0186127
                           0.006 0.008 0.1 0.095 0
                           0.8639 0.81 0.07983 0.62 0.541978
                           0.94 0.007439 0.24 0.000612 0.00624
                        </values>
                     </regular_tabulated>
         </absorption_coefficient_spectrum>
         <subsurface_scattering>
            <scattering_coefficient_spectrum>
                     <regular_tabulated>
                        <start_wavelength>0.4E-06</start_wavelength>
                        <end_wavelength>0.7E-06</end_wavelength>
                        <num_values>10</num_values>
                        <values>
                           0.2 0.94 0.81 0.62 0 0.1 0.006 0.003 0.01 0
                        </values>
                     </regular_tabulated>
            </scattering_coefficient_spectrum>
            <phase_function>
               <henyey_greenstein>
                  <g_spectrum>                     
                     <regular_tabulated>
                        <start_wavelength>0.4E-06</start_wavelength>
                        <end_wavelength>0.7E-06</end_wavelength>
                        <num_values>10</num_values>
                        <values>
                        0.027 -0.25 -0.975 -0.8 -0.96 0.62 0.81 0.094 0.18 0.05
                        </values>
                     </regular_tabulated>
                  </g_spectrum>
               </henyey_greenstein>
            </phase_function>
         </subsurface_scattering>
      </basic>
   </medium>
   
   <material>
      <name>previewmaterial</name>
      <specular>
         <transparent>true</transparent>
         <internal_medium_name>dichroic_glass_B_medium</internal_medium_name>
      </specular>
   </material>
</scenedata>

Code:

<?xml version="1.0" encoding="utf-8"?>

<scenedata>
   <medium>
      <name>dichroic_glass_D_medium</name>
      <precedence>6</precedence>
      <basic>
         <ior>1.72</ior>
         <cauchy_b_coeff>0.0018</cauchy_b_coeff>
         <absorption_coefficient_spectrum>
               <rgb>
                  <rgb>1.27 2.45 1.8</rgb>
                  <gamma>2.2</gamma>
               </rgb>
         </absorption_coefficient_spectrum>
         <subsurface_scattering>
            <scattering_coefficient_spectrum>
                     <regular_tabulated>
                        <start_wavelength>0.4E-06</start_wavelength>
                        <end_wavelength>0.7E-06</end_wavelength>
                        <num_values>10</num_values>
                        <values>
                           0 -0.25 -0.975 -0.8 -0.6 0.62 0.81 0.94 0.2 0
                        </values>
                     </regular_tabulated>
            </scattering_coefficient_spectrum>
            <phase_function>
               <henyey_greenstein>
                  <g_spectrum>
                     <regular_tabulated>
                        <start_wavelength>0.4E-06</start_wavelength>
                        <end_wavelength>0.7E-06</end_wavelength>
                        <num_values>10</num_values>
                        <values>
                           0 -0.25 -0.975 -0.8 -0.6 0.62 0.81 0.94 0.2 0
                        </values>
                     </regular_tabulated>
                  </g_spectrum>
               </henyey_greenstein>
            </phase_function>
         </subsurface_scattering>
      </basic>
   </medium>
   
   <material>
      <name>previewmaterial</name>
      <specular>
         <transparent>true</transparent>
         <internal_medium_name>dichroic_glass_D_medium</internal_medium_name>
      </specular>
   </material>
</scenedata>

Removed dichroic_glass_E cause it had wrong settings (negative absorbtion).

Would you help render Pure

?

edit; more references for dichroic glasses: http://www.worldglassnet.com/pages/appG ... subcat=All

PostS.: I edited previous codes, they weren't matching the matDB naming convention, I think that's better now. Will do a last check before upload.

dichroic glass

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