Chaos Corona Forum

Chaos Corona for 3ds Max => [Max] I need help! => Topic started by: Prem_singh on 2014-09-14, 07:14:41

Title: Fix dark edges
Post by: Prem_singh on 2014-09-14, 07:14:41

very high glossy materials getting dark at edges.
In Vray, it is an option in Vray material.
How to fix it in corona ?

Title: Re: Fix dark edges
Post by: juang3d on 2014-09-14, 09:46:00

Change the IOR to 20 or so in reflection, this should help.

Cheers

Title: Re: Fix dark edges
Post by: Prem_singh on 2014-09-15, 07:41:57

IOR is already at 50.

Title: Re: Fix dark edges
Post by: maru on 2014-09-15, 10:43:13

Could you post an example and your material? I suppose it's very lighting-dependant but maybe I'm wrong.

Title: Re: Fix dark edges
Post by: tomislavn on 2014-09-15, 10:45:00

Quote from: Prem_singh on 2014-09-15, 07:41:57

IOR is already at 50.

I guess that he meant you should lower it to 20 or some more, like 19. I used to get some weird results in my renders with fresnel IOR of 20+

Title: Re: Fix dark edges
Post by: Prem_singh on 2014-09-15, 18:04:45

Its a shader testing scene.
just a simple sphere and teapot.

Viz people HDRI no 3 was used
http://www.samples.viz-people.com/catalogs/HDRI_v1_catalog.pdf

Title: Re: Fix dark edges
Post by: Ondra on 2014-09-15, 18:34:58

Some images of setup and result would be nice...

Title: Re: Fix dark edges
Post by: Adanmq on 2014-09-15, 20:52:44

If you use 50 IOR you are introducing this curve:

(https://forum.corona-renderer.com/index.php?action=dlattach;topic=5204.0;attach=20744;image)
Reflectivity go down to 0.5 close to 90º but you have 0.92 at 0º.

So it´s normal. If you want to remove this effect use a custom curve to describe the reflections you want.

(https://forum.corona-renderer.com/index.php?action=dlattach;topic=5204.0;attach=20746;image)

Its hard to see the diference, so you can download both images and compare.
(https://forum.corona-renderer.com/index.php?action=dlattach;topic=5204.0;attach=20740;image)
(https://forum.corona-renderer.com/index.php?action=dlattach;topic=5204.0;attach=20742;image)


If you are talking about something diferent pelase post some images.

Title: Re: Fix dark edges
Post by: Prem_singh on 2014-09-16, 09:05:58

Hi Adanmq
Your first image is the result i want.
can you post a screenshot of your shader connections.

The result I am getting is

Title: Re: Fix dark edges
Post by: Adanmq on 2014-09-16, 19:27:13

Hi.
The problem is the high IOR value because the simplified Fresnel formula, You can use a custom Fresnel to drive reflections to avoid this and use a 999 IOR value (to disable corona IOR).
I use a base reflectivity of 92% to mach your 50 IOR value.

Hope this can help you.