[Bf-cycles] Cycles Fresnel behaviour

[Sergey Sharybin]

Hi,

Can't really give exact link to what Cycles use, from quick glance it it
seems to be somewhat close to what embree does.

Improvements are always possible, but it's also useful to see the .blend
file with the setup which you consider is faulty. To investigate if it's
setup properly and use for comparison of results and so.

On Mon, Jan 5, 2015 at 8:38 PM, Marco G <marco.gzt at gmail.com> wrote:

> Hi all,
> i always thought Cycles Fresnel was somewhat incorrect/weak compared to
> other engines i've used, but never got what's wrong, so I never mentioned.
> I'm still unsure if it's the case, i'd like to hear from you devs what
> about it, but seems it's really a known problem and Cycles still does not
> implement the correct approach.
>
> So, Fresnel in Cycles ("Shader A" Mixed via Fresnel Node with "Glossy
> BSDF") always gave pretty dull facing highlights, almost absent, and
> extreme reflections (and dark edges) at grazing angles. Turns out that
> making correct looking human faces, lacquered wood, floors, plastics...etc
> it's been always difficult.
> An RGB Curves node added between Fresnel and the Mix Factor has been a
> sort of solution (tuning down whites and raising blacks), but a proper
> implementation should be priority IMHO.
>
> Example human head with highlighted errors, current Cycles behaviour:
> Head_Fresnel <https://db.tt/gaO1ZUBu>
>
> I stumbled upon these slides below, which exactly explain (and solve) this
> problem, page 29-34, the same head is used for demonstration. CC Lee Perry
> Link slides: Slides Anders L.
> <http://blog.selfshadow.com/publications/s2014-shading-course/langlands/s2014_pbs_alshaders_slides.pdf>
>
> As you can see by using a correct approach, the dark artifacts and dull
> front highlight problems are gone, the slides says "for rough BSDFs you
> really need to do it based on the normal of each microfacet (i.e, the
> half-angle vector) and the light direction" page 31.
>
> Is this the case or am i missing something? Could this be improved by
> implementing such method?
>
> Thanks,
> Regards. MG
>
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>
>


-- 
With best regards, Sergey Sharybin
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