hatrick Posted February 1, 2009 Share Posted February 1, 2009 (edited) Hi, Another noobquestions on mantra... I ve problems with glossy materials(standard reflective)...I m getting crunshy highlights ore blownout reflections(sparcles) although i ve increased the render and lightsamples...i use PBR thx linebend_x.hipnc Edited February 1, 2009 by hatrick Quote Link to comment Share on other sites More sharing options...
Jason Posted February 1, 2009 Share Posted February 1, 2009 Hi,Another noobquestions on mantra... I ve problems with glossy materials(standard reflective)...I m getting crunshy highlights ore blownout reflections(sparcles) although i ve increased the render and lightsamples...i use PBR thx You might try: increase your Reflect Limit, and/or play with the Color Limit rendering parameter. I'm not sure how much these will help you, but they're worth a shot. Quote Link to comment Share on other sites More sharing options...
hatrick Posted February 1, 2009 Author Share Posted February 1, 2009 hi jason, could you please give me some more details on that issue...what causes the white sparcles...are there elementary mistakes in my setup thank you Quote Link to comment Share on other sites More sharing options...
anamous Posted February 1, 2009 Share Posted February 1, 2009 (edited) There's two aspects contributing to this issue: - path tracers tend to produce these bright spots when the path misses light sources or (depending on the light falloff function) hit the exact center of the light source. This is normal and can be worked out by applying a maximum limit to the energy contribution of a path - which is what the color limit basically does. Per default it is set to 1024, which is ridiculously high for most cases (though accurate). For most scenes you will want to lower this. You scene specifically doesn't need more than let's say 3. You can add this parameter by using the "rendering parameters" drop down on the Mantra ROP and selecting "color limit" from the folder "Mantra 9.5", then clicking on the arrow that points from left to right. - specular and reflection are the same in PBR. A specular call will reflect everything and every light, and a reflection call, too - this is the correct behavior, since "specular" as it is used in CG is just a computationally cheap shortcut to the reflection of light sources. Currently, you have set up your reflective shader to do both specular and reflection, which is basically the same, and it adds them together. In the micropolygon and raytracing engine, this setup is correct. In PBR however, you end up with double the reflection which makes it very, very bright. I dialed down one of those parameters to 0. Is this how your scene should look like? cheers, Abdelkareem linebend_x.hipnc Edited February 1, 2009 by anamous Quote Link to comment Share on other sites More sharing options...
hatrick Posted February 1, 2009 Author Share Posted February 1, 2009 hey thx a lot ! very good description!.... one more question ... how can i control the lightsourcereflection seperatly with PBR? do i need a seperate lightsource with no diffuse contibution ? Quote Link to comment Share on other sites More sharing options...
anamous Posted February 1, 2009 Share Posted February 1, 2009 Controlling light contributions in PBR still is pretty much in development, but in this case, to disallow the area light from appearing in the "specular" reflections, you should turn off the "specular contribution" switch on the light source. cheers, Abdelkareem Quote Link to comment Share on other sites More sharing options...
hatrick Posted February 1, 2009 Author Share Posted February 1, 2009 ok ... sorry ... just to get sure ... the reflections and the specular controls do exactly the same with PBR ... Quote Link to comment Share on other sites More sharing options...
anamous Posted February 2, 2009 Share Posted February 2, 2009 (edited) ok ... sorry ... just to get sure ...the reflections and the specular controls do exactly the same with PBR ... That's not what I meant. Depending on the shader, the "specular" and "reflection" parameters could be weighted differently for example - in the context of traditional rendering, this makes some sense. However, in the context of PBR, both return the same visual results - a specular reflection in the physical meaning. I assume that the shader you are using sums these two terms, thus having double the amount of specular reflection - a quick fix is to turn off one of the two specular reflections. A correctly constructed PBR shader will only have one specular reflection term and apply the appropriate (fresnel etc.) weighting to it. cheers, Abdelkareem Edited February 2, 2009 by anamous Quote Link to comment Share on other sites More sharing options...
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