<div dir="ltr">There are no issues i guess, Cycles just uses quite simple and fast fresnel evaluation from the beginning and was never reviewed since then.<div><br></div><div>Will have a closer look later this week.</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Jan 5, 2015 at 11:10 PM, Matthew Heimlich <span dir="ltr"><<a href="mailto:matt.heimlich@gmail.com" target="_blank">matt.heimlich@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Cycles' Fresnel term is definitely different than most other renderers I've used, which is why I almost solely use "facing" from an artistic point of view. Not a huge deal I don't think, unless working with real-world absolutes (in which case a spectral renderer should be used anyway), but it would be interesting to hear what the issue is that causes this disparity in Cycles.</div><div class="HOEnZb"><div class="h5"><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Jan 5, 2015 at 11:35 AM, Sergey Sharybin <span dir="ltr"><<a href="mailto:sergey.vfx@gmail.com" target="_blank">sergey.vfx@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Hi,<div><br></div><div>Can't really give exact link to what Cycles use, from quick glance it it seems to be somewhat close to what embree does.</div><div><br></div><div>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.</div></div><div class="gmail_extra"><br><div class="gmail_quote"><div><div>On Mon, Jan 5, 2015 at 8:38 PM, Marco G <span dir="ltr"><<a href="mailto:marco.gzt@gmail.com" target="_blank">marco.gzt@gmail.com</a>></span> wrote:<br></div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div><div dir="ltr">Hi all,<div>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.</div><div><br></div><div>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.</div><div>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.</div><div><br></div><div>Example human head with highlighted errors, current Cycles behaviour: <a href="https://db.tt/gaO1ZUBu" target="_blank">Head_Fresnel</a></div><div><br></div><div>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</div><div>Link slides: <a href="http://blog.selfshadow.com/publications/s2014-shading-course/langlands/s2014_pbs_alshaders_slides.pdf" target="_blank">Slides Anders L.</a></div><div><br></div><div>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.</div><div><br></div><div>Is this the case or am i missing something? Could this be improved by implementing such method?</div><div><br></div><div>Thanks,</div><div>Regards. MG</div></div>
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<br></blockquote></div><span><font color="#888888"><br><br clear="all"><div><br></div>-- <br><div><div><span style="color:rgb(102,102,102)">With best regards, Sergey Sharybin</span></div></div>
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<br></blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature"><div><span style="color:rgb(102,102,102)">With best regards, Sergey Sharybin</span></div></div>
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