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Kerkythea Rendering System • View topic - Need explanation with complex IOR / NK data
Page 1 of 1

Need explanation with complex IOR / NK data

PostPosted: Tue May 15, 2012 10:56 am
by anar
Hi all,

I'm desperately trying to understand how materials using complex IOR / NK data are made.
I had a close look at Alex's NK metals and especially the Gold one.
I also looked at his RoseGold NK mat and compared.
Still I just don't understand at all...

When I have a look at the Gold NK here is what I see :
- RGB values for the Fresnel Conductor's IOR are : 32-100-255
- The corresponding numerical value is 1.601

And when I have a look at the RoseGold mat here is what I see :
- RGB values for the Fresnel Conductor's IOR are : 147-255-255
- The corresponding numerical value is also 1.601 :shock:

How is this possible ?
When I try to make my own gold mat based on Alex's Gold NK, if I change the IOR RGB values the numerical value get changed accordingly...
How have these two different gold mats been made ?
How can they have a different IOR RGB values but still have the same numerical value ?
This is a complete mistery to me...
Or maybe I am missing something ?

Alex if you read this, could you please give me a little explanation ?

Thanks !

Re: Need explanation with complex IOR / NK data

PostPosted: Wed May 16, 2012 7:07 am
by anar
OK I finally found out how this is done...
Thanks for your reading.

Re: Need explanation with complex IOR / NK data

PostPosted: Wed May 16, 2012 7:55 am
by tridem
Hi anar, the way nk data work in kerkythea is really difficult to understand...I gave up a while ago, but if you can explain what you achieved would be great :grin:

Re: Need explanation with complex IOR / NK data

PostPosted: Wed May 16, 2012 9:34 am
by anar
Hi Tridem,

I could explain my tweaking and what I came with but I'm afraid it might not be the proper way to go...
I've mainly tried to guess with several tries and errors and maybe the result I have is not good at all !
So I hope someone better than me (Alex or Patricks ?) won't blame me for what I'm gonna describe.

If for ex. you want to do a Red Gold :
1) You need to have a gold NK file. Copy it in KT's n-k library
2) Look at an allready done NK mat. Alex's NK Gold for ex.
3) Now start your own. Matte/Phong with Fresnel Conductor in Specular, None in Spec. Attenuation, Spec. Sampling turned on and adjust Shininess as desired
4) In Fresnel Conductor Options adjust IOR color as desired. For a red gold choose the opposite color (green). Don't choose any N-K File for now...
5) Save your mat
6) Open your mat in a text editor and write down the IOR RGB values on a paper. If you don't, you can find them back as they are RGB divided by 255 I think...
7) Add the name of your gold NK file in <Parameter Name="N-K File" Type="String" Value="your_NK_file.nk"/> and Save
8) In KT reopen your mat. You will see that your IOR colors have been changed because of the N-K file. Don't mind. Just remember the IOR numerical value (1.601 for Gold) and save your mat again
9) Reopen it in a text editor and put back the RGB values you have previously write down at stage 6) and save
10) Delete your_NK_file.nk from KT's n-k directory and in KT reopen your mat
11) Update the IOR numerical value with the correct one you noticed in stage 9) (1.601 here...) and save your final mat
You now should have a Red Gold...

Please Tridem don't take this as the regular way to do it !
What I can achieve this way is having a constant IOR numerical value while having different IOR colors like in Alex's Gold vs RoseGold...

And please KT masters don't blame me if what I describe is not good but explain us instead !
This has been asked a lot of time in the forum but nobody never ever had the desire to answer us...
Like if it was a well kept secret.

Tridem, I hope this will help you and others.

Edited : Stage 8 has become a smiley but it was not my intention...

Re: Need explanation with complex IOR / NK data

PostPosted: Wed May 16, 2012 9:49 am
by tridem

Re: Need explanation with complex IOR / NK data

PostPosted: Wed May 16, 2012 10:26 am
by anar