Zap's "energy conservation law" ???

#1

Hi! Does anyone understand what Zap from mental images mean in this energy conversation law? How do we make use of this info? So if I have a reflection of 80%, I need to reduce mu diffuse colour to 20% in my material?

#2

Most modern renderers use shaders that follow this physically accurate law. so a real-world material obviously can’t be 100% diffuse/reflective/refractive all at the same time. There are ways to break the law, of course, but the renderer will automatically calculate appropriate values. So a lot of beginners might ask ‘why is my 100% reflective shader not red like my diffuse channel’ This is the energy conservation law at work. If the material is 100% reflective, then it has no diffuse value. If it is 100% diffuse, then vice-verse. On so on…

Of course, this isn’t entirely accurate inside the shader/renderer, because real-world materials are much more complicated than this and are never 100% anything, but it gives us a good head start.

Plus, if you bear the law in mind whilst creating your shaders, it will lead to alot less confusion/frustration when your rendered materials behave completely differently than you might expect.

#3

I guess you’re asking if it’s something you have to take care of when creating shaders - no, just create them, it’s the renderer’s part to calculate ray contribution based on this law.

#4

So I have to balance the percentage for the visibility between all 3 channels? ( Diffuse/Reflective/Refractive. How do I get a colour reflective material to show the colour and yet somewhat have high reflectivity? If I turn the diffuse down, it looks more darker. Sometime the colours from the reflection will over power the materials diffuse colour and it became like a mirror. If I turn the reflec down… I lose the reflective details…

I’m still working with standard shader with scanline because of company workflow…

#5

As pokoy said, the renderer will automatically adjust for the law of energy conservation. However, as I said above, you have to approach shader-creation using a real-world approach. The renderer is attempting to generate a physically accurate render, so you have to do your part and create your shaders/lighting based on real-world observations. As for reflections, the all-important factor is the index of refraction. In MR I believe this is in the BRDF section of A&D material.(I use Vray) You must setup your reflective materials(every single element in the real-world has reflective properties) using correct fresnel falloff. It’s all very complex to get into in a thread so I suggest you do some research. And always use reference imagery of the material you are trying to create the same way you would when modeling/texturing/sculpting.

#6

Sorry, I only just read the last bit of your post. If that’s the case then disregard all we’ve said. :slight_smile:

If you’re still working with standard shaders/scanline then nothing is based on physical accuracy at all.
The standard material/scanline has absolutely no relationship to the law of energy conservation. This kind of legacy shading/lighting workflow dosn’t work in linear colour space and it was entirely up to the artist to hack/fake/create lighting shader/lighting setups to achieve certain effects. Correct light falloff, reflective/refractive properties, global illumination, etc. This isn’t to say that legacy setups are completely shit, some artists still use it to good effect.(although they are few and far between these days)

Basically, if you are using the standard material with raytrace reflection, you will have to fake it. Start by creating a raytrace material, apply a falloff map in the reflect slot, and adjust the output curve to mimic the materials IOR.

Incidentally the Raytrace material is a pretty good old-school shader. It was created by the blokes who went on to develop the Brazil render engine.

#7

IC. So its still boils down to observation of the material in the real world and matching/ recreating it in 3D. So what Zap talk about in the energy conservation law is more in depth and tech of light energy. As for designer/artist, we just have to use our eyes to match the looks from the really world. Correct?

#8

This is pretty much it in a nutshell. We can observe and understand the law, and try to use it to our advantage to create more believable materials.

#9

Here’s some extra info, basically stuff that’s already been gone over:

http://www.neilblevins.com/cg_education/energy_conservation/energy_conservation.htm

But please change the name of this topic. Zap did not invent the law of energy conservation :slight_smile:

  • Neil
#10

Thanks soulburn3d! That was a good read. Now I know what to look out for when I creating the shader in scanline.