CGTalk > Techniques > Lighting and Shaders
Login register
Thread Closed share thread « Previous Thread | Next Thread »  
Thread Tools Search this Thread Display Modes
Old 05-28-2010, 09:15 AM   #1
misterwolfy's Avatar
wolfy wolfson
Join Date: Mar 2009
Posts: 313
fresnel reflection

Why are reflections brighter on edge then straight on, described as the Fresnel reflection effect? From a "scientific" perspective.

Does the amount or quality of this effect change on certain materials in a predictable way? Is there some sort of Fresnel index table?
Old 05-28-2010, 12:39 PM   #2
Lord of the posts
playmesumch00ns's Avatar
render monkey
pretty picture maker
United Kingdom
Join Date: Jul 2002
Posts: 3,420
It's really rather complicated to be honest and has to do with the interaction of photons with the electrons in the atoms at the interface to your material. There's no intuitive explanation that I've come across.

What is important about it is that the fresnel equations tell you the probability of a photon being reflected, transmitted or absorbed at an interface, or to think about it another way, what proportion of the incident light is reflected, transmitted or absorbed.

This proportion is dependent on the angle the light hits the surface at, and the index of refraction of the surface. That is why reflections appear to get brighter at grazing angles - because more of the light is being reflected rather than transmitted, while 'in the middle of an object' the reverse is true.

Another important consequence of the fresnel effect is that glossy reflections tend to get sharper at glancing angles as all reflection directions apart from the mirror direction get cut out.

There's some more explanation of this in the 'science of cg' thread that's stickied on this forum, as well as links to tabulated ior data for different materials.

You can have your characters photoreal, fast or cheap. Pick two.
Old 05-30-2010, 12:29 PM   #3
Ludwigshaven, Germany
Join Date: Mar 2010
Posts: 71
If I remember correctly the fresnel effect is mainly based on the index of refraction. So you can use tables like the following to adjust your materials.
RenderPal V2 - Render Farm Manager
- Version 2.14 Out Now!
Official Team member
Old 05-30-2010, 12:29 PM   #4
CGTalk Moderation
Lord of the posts
CGTalk Forum Leader
Join Date: Sep 2003
Posts: 1,066,478
Thread automatically closed

This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.
CGTalk Policy/Legalities
Note that as CGTalk Members, you agree to the terms and conditions of using this website.
Thread Closed share thread

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Society of Digital Artists

Powered by vBulletin
Copyright 2000 - 2006,
Jelsoft Enterprises Ltd.
Minimize Ads
Forum Jump

All times are GMT. The time now is 06:12 PM.

Powered by vBulletin
Copyright ©2000 - 2016, Jelsoft Enterprises Ltd.