"Everything has fresnel!"

[michae]

I was just curious on peoples workflow when it comes to using fresnel reflections. I was wondering if you guys always turn on"Use Fresnel" for reflections whether your making just rubber shader where you mainly see just highlights to a chrome shader or does it just fall back on the "what ever looks good" approach.


Michael

[glorybound]

Well, for me, everything looks better when I turn Fresnel on everything. I'm sure someone could argue both sides.

I was just curious on peoples workflow when it comes to using fresnel reflections. I was wondering if you guys always turn on"Use Fresnel" for reflections whether your making just rubber shader where you mainly see just highlights to a chrome shader or does it just fall back on the "what ever looks good" approach.


Michael

[joconnell]

I use the falloff map in max to push the fresnel effect for drama so you get a very obvious gradient between reflective and not, mainly for style reasons though. If you've a good environment things tend to default towards very realistic which is a nice place to start. Metals don't use the fresnel curve, they use a way more complex curve which is almost flat from front until you get to the edge, then there's a slight dip before it shoots up to 100% reflective. It's also a slightly different curve for the red, green and blue portions of the material so most people settle on using a fresnel with a really high ior (25 upwards) or just use a flat colour for the reflection strength and no fresnel at all. Here's a reflectance curve for three different materials from wikipedia - would be hard enough to get with a fresnel curve!

[Morbid Angel]

would be cool to have ability to load those curves as fresnel.

[vlado]

You can load them in a Ramp or Gradient map to use as reflection strength.

Best regards,
Vlado

[joconnell]

That's one thing that max lacks - maxscript access to the output curve which could give you a sneaky way to do it. Must look into mapping gradient ramps to falloffs for this. Vlado is that type of curve data readily available for a lot of metals? It's not something I'd have thought about before but it'd make sense if there was a handy table of data like an ior table with numerical data that could be changed into luminance values for a ramp?

[Dariusz Makowski (Dadal)]

I use the falloff map in max to push the fresnel effect for drama so you get a very obvious gradient between reflective and not, mainly for style reasons though. If you've a good environment things tend to default towards very realistic which is a nice place to start. Metals don't use the fresnel curve, they use a way more complex curve which is almost flat from front until you get to the edge, then there's a slight dip before it shoots up to 100% reflective. It's also a slightly different curve for the red, green and blue portions of the material so most people settle on using a fresnel with a really high ior (25 upwards) or just use a flat colour for the reflection strength and no fresnel at all. Here's a reflectance curve for three different materials from wikipedia - would be hard enough to get with a fresnel curve!

Interesting point. So do you think that RGB reflection could possible have slightly different IOR per R,G,B rays or its that same across all channels?

[joconnell]

I've seen data for some metals where it definitely does - It's possibly more complex than just rgb but yeah there's a tiny bit of variation in the three colours across the surface which gives you slight chroma splitting effects.

[Dariusz Makowski (Dadal)]

Humh interesting. So Vlado/Chaos is there a way to plug a separate IOR map in to each of RGB channels for reflections - asking because stuff like that will affect very dramatically flakes/car paints accuracy/realism.

Thanks, bye.

[vlado]

Humh interesting. So Vlado/Chaos is there a way to plug a separate IOR map in to each of RGB channels for reflections - asking because stuff like that will affect very dramatically flakes/car paints accuracy/realism.

If you go the ramp/gradient route, then there is no need to - you have full control over the reflectivity for red/green/blue (or you can use a separate falloff map for each channel). I don't think the actual physics is as simple as separate IOR for red/green/blue though.

Best regards,
Vlado

[Yannick]

Hi Vlado,
when you say the ramp/gradient way. is it just a matter of plugin a ramp in the reflection colour?

Thanks.

[andybot_cg]

I'm wondering if there's a bit of confusion in this thread.
If you notice - it's alum, silver and gold on the graph - not RGB...

[joconnell]

Yep sorry andy you're right - they aren't an RGB graph for a single metal, I didn't make that clear, it's a single curve for each material as you say. I've seen a few of those graphs though where for a single material they separate the RGB curves though, sorry for any confusion caused.

[vlado]

Is it just a matter of plugin a ramp in the reflection colour?

Yes; either in the color or in the Amount.

Best regards,
Vlado

[Yannick]

but a ramp plug in the colour would follow the UV of the geometry...