Re: Re: Fresnel effects -- plugin tool 2004-01-20 - By nospam2
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Hello Eric,
EW> You can easly do a simple test. Drop two infinite planes in a scene. Make
EW> one checkered, the other transparent with an index of refraction for water
EW> (but no reflection)
Hmmmm... Not a good example. If your put reflection to zero, null, nada, rien,
....
EW> , and make it a little higher than the first. Add the sky
EW> atmosphere (so you have something to reflect). Render. No matter where you
EW> place the camera, that plane of water will never reflect the sky.
... of course the wplane will never reflect anything.
But styill it is an example, becaus ethe Fresnel effect doesn't only predict
that the sky will be reflected, but that a low incidence it will be impossible
to see the bottom of the lake.
And this should be easily tried out.
Anybody volunteer to try that physical property uin carrraa ?
EW> All you
EW> see is the checkered plane underneath. In the real world, you would see the
EW> sky reflected in the water.
EW> Now maybe it should provided that functionality in the box, but you could
EW> argue that about lots of features that the 3rd party plug-in developers
EW> provide.
EW> Regards,
EW> Eric Winemiller
EW> Digital Carvers Guild
EW> 3D plug-ins for Carrara
EW> http://digitalcarversguild.com
EW> -- -- Original Message -- --
EW> From: "nospam2" <nospam2@(protected)>
EW> To: "m3d242" <Carrara@(protected)>
EW> Sent: Tuesday, January 20, 2004 3:34 PM
EW> Subject: Re: [Carrara] Re: Fresnel effects -- plugin tool
>> Hello m3d242,
>>
>> >> What's called the Fresnel effect is in fact nothing but another way to
>> m> describe the refraction indice of the material.
>>
>> m> That's incorrect. The Fresnel effect and the index of refraction are
EW> not the
>> m> same thing.
>>
>> See my just previous post.
>> The Fresnel effect is not the same thing than refraction, true : it is a
EW> consequence of refraction.
>> It is the result that sinus being bounded by -1 and +1, at low angle the
EW> ray cannot enter the material having an higher refraction indice and then is
EW> totaly reflected instead of being partly reflected and partly refracted.
>> SInce Carrara takes refraction into account, how is it that it cannot
EW> produce the Fresnel effect ?
>>
>> What I mean is : to calculate the Fresnel effect, one only need the light
EW> ray angle of incidence and the refraction indice of both material (air and
EW> water for example).
>> Since Carrara already knwos all that, I don't see the point for an extra
EW> plug-ins.
>>
>> >> Since refraction is one of the shaders channels in Carrara, I do'nt see
EW> why
>> m> the effect would not be rendered by the rendering engine.
>>
>> m> The Fresnel effect is the roll off of transparency to
>> m> reflectivity (or reflectivity to
>> m> transparency) on the surface of an object depending on the viewing
EW> angle.
>> m> The index of refraction takes into account how light bends (or
EW> refracts) when
>> m> passing through and object. The index of refraction has noting to do
EW> with how
>> m> reflecive an object is.
>>
>>
>> What you call the roll off of transparency to reflectivity is not a
EW> property per se. It is just a consequence of the refraction law.
>> In the absolute, a transparent object could have a zero reflectivity
EW> indice and still produce the Fresnel effect.
>> If you look at this imaginary object straight from the top, you see
EW> through it. Then as the angle of vision get smaller (= tangential to the
EW> object surface), at some point you would stop seeing through it (this
EW> property is used in the optical fiber).
>> That is the Fresnel effect.
>>
>> Of course, in the reality, all objects have some reflection property. SO,
EW> obviously, at the angle when there is no more refraction, all the light is
EW> reflected.
>> that is why the Fresnel effect is associated with reflection in people
EW> minds. But it is a consequence of the refraction law, not the reflection
EW> law.
>>
>>
>> --
>> Best regards,
>> nospam2
>> mailto:nospam2@(protected)
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