[rubbin]

Hello

Physics says that the Index of refraction is the ND + K

K it is the coefficient of extinction

So, it si supposed as I understand it that K parameter refers to the amount of energy that a material absorbs.
So, what I do not understand is why whenyou increase the value of K the reflections are brighter when it is supposed to be weaker isn´t it?

Thanks

[Mihai]

As I understand it, the K parameter works in conjunction with the nD. So you can't just change the K and expect a realistic reaction. It was added in order to better mimic metalic materials and avoid a darkening at the very edges of the viewing angle. I don't suggest to change it arbitrarily but instead look online for nD + K values for materials. For dielectrics (non conductive materials) use only the nD, and it will behave predictably. K is only ment to be used for creating metals.

[rubbin]

Thanks for the answer but my question goes further. In physics, k paramater it is kown as the coeficient of extinction as his name says it is supposed that controls the amount of energy of the light that extincts once the light hits one material, so in maxwell when you increases the k value the material becomes more brighter instead of darker, that is what i do not understand. Thanks

[rubbin]

Please somebody?

[tom]

http://en.wikipedia.org/wiki/Mathematic ... of_opacity

As the energy gets absorbed, the material becomes opaque. If it's not absorbed on the surface, it starts to travel inside the object and the object becomes transparent.

[rubbin]

Thanks for the answering, but what it has to be with the strenght of reflections in metals? Why it is recomended to use the k parameter only with metals? Can somebody from next limit explain this, How the K parameter Works in real life? THANKS

[Half Life]

K is an imaginary value -- so how it works in real life is: it doesn't.

[rubbin]

Yes it does. If it was not this way why maxwell uses it? Of course K parameter has influence in real life, need somebody to explain and make it clear

[Half Life]

Using that logic you could just as easily say that such a thing as bump maps, or normal maps, or even roughness and anisotropy exist in the real world because Maxwell has validated their existence. All of those parameters are highly idealized mathematical approximations -- they exist solely so we can easily get to something that has the "look" of reality... however it is important to understand that it is not even close to the level of complexity reality is. Moreover this is far from a perfected science -- new developments in our understanding are happening all the time, so you have to expect Maxwell will evolve as the science and mathematics behind this simulation evolve.

Bottom line: Why is K in Maxwell? Because it is needed to remove the dark edges from metal materials -- nothing more, nothing less. The easiest thing to do is ignore it beyond that usage.

If that is not good enough for you, then my best suggestion would be to get a degree in physics and come back showing why they are wrong. Because insisting they are holding out on information when you don't know the answer yourself is pretty messed up.

Also, for what it is worth, there is more than one type of extinction coefficient... they may have the same name, but they are for different applications. The K in Maxwell is a modifier for Nd to form a simple type of complex IOR -- the other type (sometimes known as molar extinction coefficient) is more like something you might imagine being used in SSS (however Maxwell doesn't work off that system which is more chemistry based).

The link Tom gave you is the right one -- and honestly, there is nobody I know more qualified than Tom to tell you how Maxwell's material system works.

[dariolanza]

Hello Half Life,

Yes, the K concept exists in real world. It is the absorption loss as it is described here:

http://support.nextlimit.com/display/mx ... -+ND+and+K

As the refraction index itself, this is an specific characteristic of a material that is be measured on lab.
Any accurate physical description of a surface takes this concept into account, although it is usually too picky for most uses.

Dario Lanza

[Half Life]

Hey Dario,

The K value is a mathmatically derived value, the actual lab mesurements do not find a K value... it is created as a results of math and the measurements, however the value itself cannot be measured. This is why it is imaginary.

http://en.m.wikipedia.org/wiki/Kramers% ... g_relation

Best,
Jason.

[Bubbaloo]

It sure makes pretty pictures though!

[Half Life]

No doubt! Every time I show Maxwell to other (non-3D) artists they always respond with "that is a render?!?". It's pretty cool...

Best,
Jason.

[rubbin]

Well, thaks for the answering but my opinión is that when sombody uses phisycs terminology as K and then it is used only to remove dark edges in metals something Works wrong. I insist in this because Maxwell it is supposed to work understanding the bahavior of light as it Works in real life but with your answering it seems to me that in Maxwell it si not as true as the want us to believe it. Is it right?

Thanks again

[Fernando Tella]

Hey Dario,

The K value is a mathmatically derived value, the actual lab mesurements do not find a K value... it is created as a results of math and the measurements, however the value itself cannot be measured. This is why it is imaginary.

http://en.m.wikipedia.org/wiki/Kramers% ... g_relation

Best,
Jason.

Just like speed, you just measure position an time and speed value is derived mathematically. Is speed imaginary?