# METAL material values

Hi all,

I have 2 questions about the METAL material:

1) What are the maximum values for "specularity" and "roughness". I would
like to confirm if the maximum value for specularity is 1.0 (or maybe more?)
and if the maximum value for roughness is 0.5 (although I have found in some
web links that roughness values greater than 0.2 are not realistic)

2) I need to create 2 metallic materials.

a) The product data for the first metal is the following:

- Minimum % Total Reflectivity: 95
- Image Clarity: 95
- % Diffuse Reflection: <12
- Specular reflictivity%: 90

I'm assuming that this material can best described as follows:

void metal metal_1
0
0
5 .95 .95 .95 .90 .10

b) The product data for the second metal is the following:

- Total Reflection %: 94
- Total Reflection: 94
- % Diffuse Reflection: 80-90
- Specular reflictivity%: 90

I'm assuming that this material can best described as follows:

void metal metal_2
0
0
5 .94 .94 .94 .90 .85

Could someone confirm if I'm on the right track?

Thank you so much in advance!

Best,

···

--
DDes I MDes I Barch

I'm assuming that this material can best described as follows:

void metal metal_1
0
5 .95 .95 .95 .90 .10

Sorry, you are close, but this would give a strange result. the .90 is fine and tells radiance that 90% is specular, 10% is diffuse reflectance. The .10 does not work. Roughness is not the same as diffuse reflection. Diffuse reflection is already defined as the difference betwenn specular reflection and 1. Roughness is more or less a visual effect simulating uneveness of a surface. Set it to zero for your application.

The same for your second example, set the rgb values to the total reflection, define the specular component (which is low in the second example), so the rest is diffuse.

Good luck, Lars.

Then, my question is: what is the difference between "Total Reflection %"
and "Specular Reflectivity %", and how does this translate in the METAL
material values?

Hm, I hope I do not write something wrong now...

The total reflection is the relation of energy reflected to the energy
that is hitting the surface. 100 hit the surface, so, if total
reflectivity is 95%, 95 leave it.

Specular reflectivity is the part of what is reflected that is leaving
the surface in a directed manner. So to go on with our example, is 95%
was the total reflection, and the specular reflectivity is 90%, of the
100 hitting the surface 0.9*95=85.5 leave the surface as specular
reflection. That also means that the remaining 0.1*95=9.5 leave it as
diffuse.

My total unitless numbers would all translate into radiance Watt / (sr *
m2).

My other question is still about the value ranges:

What are the maximum values for "specularity" and "roughness". I would like
to confirm if the maximum value for specularity is 1.0 (or maybe more?) and
if the maximum value for roughness is 0.5 (although I have found in some web
links that roughness values greater than 0.2 are not realistic)

Specularity cannot be more then 1, as you cannot have more energy
reflected as specular then energy reflected in total. If you replace the
maximum 1.0 by 100% you will understand.

As far as I know you are right about roughness, but it is difficult to
estimate this parameter, and I treat it more as a visual effect...

CU Lars.

Hi Lars,

Thank you so much for your time! This has been extremely helpful.

Best,

···

2008/8/21 Lars O. Grobe <[email protected]>

> Then, my question is: what is the difference between "Total Reflection %"
> and "Specular Reflectivity %", and how does this translate in the METAL
> material values?

Hm, I hope I do not write something wrong now...

The total reflection is the relation of energy reflected to the energy
that is hitting the surface. 100 hit the surface, so, if total
reflectivity is 95%, 95 leave it.

Specular reflectivity is the part of what is reflected that is leaving
the surface in a directed manner. So to go on with our example, is 95%
was the total reflection, and the specular reflectivity is 90%, of the
100 hitting the surface 0.9*95=85.5 leave the surface as specular
reflection. That also means that the remaining 0.1*95=9.5 leave it as
diffuse.

My total unitless numbers would all translate into radiance Watt / (sr *
m2).

> My other question is still about the value ranges:
>
> What are the maximum values for "specularity" and "roughness". I would
like
> to confirm if the maximum value for specularity is 1.0 (or maybe more?)
and
> if the maximum value for roughness is 0.5 (although I have found in some
web
> links that roughness values greater than 0.2 are not realistic)

Specularity cannot be more then 1, as you cannot have more energy
reflected as specular then energy reflected in total. If you replace the
maximum 1.0 by 100% you will understand.

As far as I know you are right about roughness, but it is difficult to
estimate this parameter, and I treat it more as a visual effect...

CU Lars.

_______________________________________________