Control Energy Conservation ?

[CinnamonMetal]

How can I control the Energy Conservation in Mantra ? If anyone remembers mILA it had a energy conservation control, I think mILA was the pioneer for PBR, no one payed attention at the time as everyone was focused on Arnold.  

[LaidlawFX]

If you look at the BSDF in the principal shader you'll see how it controls the levels. I can't explain if mathematically, but it will balance the load for you. If you work with all the sliders for the different contributions and pretend they all represent part of a percent it will make sense. If you overload one of those values or all of them they will progressively flatten the values.  

[CinnamonMetal]

@LaidlawFX Maybe you can help me understand two things.  I understand you can supply sRGB values Specular Color, for example; water has a Specular Color of sRGB(38,38,38) but linear it's 0.02, what color system must I use to strictly work with linear color values ?

[LaidlawFX]

In general you should not use any non-linear textures in the shaders with a true PBR workflow. Then your float value and pixel values will line up correctly. Houdini is setup to assume a linear light workflow through the whole program. When you author them in Photoshop or whatever program you should apply the correct method for your texturing workflow upon export, or as a post conversion, so they are read in linear. Houdini nor most DCC have the full range of options to compensate for all of the different color spaces a texture can be authored in. Generally you can apply a gamma shift or sRGB shift in most programs. Houdini to my knowledge still does not have a sRGB to linear vop node to compensate. Though if you are worried about this already to this extent, you should do the correct conversion from the export to begin with then all the math will work out.   

I'm sure you are aware of Linear Light workflow, but this document speak directly to it as far as Houdini handles it : http://www.sidefx.com/docs/houdini/render/linear.html It's helpful as a reference guide, the core math is slightly beyond me to explain. I still can't describe a quaternion, lol.

 

[CinnamonMetal]

I'm familiar with linear workflows. What I meant was color picking, rather then picking the color in an sRGB value; how do you pick a color in linear values ?

[LaidlawFX]

If you are picking the color in Houdini you are picking it in linear space. If you want to pick it as a float versus a vector, you can wire a float into the input. Then you can enter just .02, or just enter .02 in all three values as the values are 0-1, not in 256 numeration.

[CinnamonMetal]

I was under the impression when picking colors, it was in sRGB values