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Brief Consideration About Materials

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Date Added: 30th December 2010

Specular reflection is where the light comes in and reflects out from the surface at the same angle (Fig.06).

Fig. 06

In reality both type of reflection will coexist on most objects, varying on intensity from one type of surface to another (Fig.07).

Fig. 07

The shader will use the information contained in the Diffuse texture to define how the light that hits an object is partially absorbed by its surface and also diffusely reflected. And the Specular texture will define how the specular reflection will happen (Fig.08).

Fig. 08

But, if both Diffuse and Specular are types of reflection that coexist on any surface, why aren't they only one, and why may they have different colors? As in this case where we've got a chess pawn with a brownish (wood) diffuse reflection and a white specular reflection (Fig.09).

Fig. 09

At this point important information needs to be added to this equation. Physical/chemical characteristics of a material will affect how the light behaves when hitting its surface. Depending on the material's nature, the specular reflection may remain true to the original color of the light, or may be tinted by the color of the object (Fig.10).

Fig. 10

So, in this example, the specular reflection on the toy and the chess piece maintains the original color of the light (white), while the specular reflection on the door knob or the Christmas tree ball is tinted by the objects' colors.

How so? For the purpose of our needs, we may reduce the materials to two basic different types: Dielectrics and Conductors. Dielectric materials do not conduct electricity. Conductors do. So, in a very non-scientific way that should only be used by artists and not someone writing a science paper, we could say that Conductors are all the metals or metallic looking surfaces, and Dielectrics are all the non-metallic surfaces, such as wood, plastic, rubber, clay, fabrics, etc (Fig.11).

Fig. 11

And what is interesting for us to know is that Conductors alter the color of the specular reflection, tinting them. While the Dielectric materials will be neutral to the light and not affect the color of the specular reflection.

In the case of the Christmas tree ball, while it is made of plastic it still has a metallic look and that's because it was painted with a metallic finish. So it's made to look like metal. The same way if something made of metal is painted with a truly opaque paint, they will reflect as dielectric, and not as conductor, because the external layer that is reflecting the light is not of a conductive nature (Fig.12).

Fig. 12

Please note: There is some very interesting information on the web showing how the electrons of conductor or dielectric surfaces are aligned in specific ways and how it affects the light that bounces on them. But for the solely artistic purpose of this study, knowing that it happens, and not all the details of how it happens, is enough.

So, if you want to create a material in 3D that truly recreates the physical aspects of an existing material, you have to understand its nature and how it affects the light.

Ok, we understood how real world materials behave, but how you replicate that in 3D?

In order to do that we must get one bit of technical information. It is very important for us to know that, during the rendering, diffuse and specular will be calculated on two separate moments. First the diffuse reflection will be calculated, then the specular reflection. Then, right after that, one is added to the other for the final result and the object is finally drawn on screen (Fig.13).

Fig. 13

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Readers Comments (Newest on Top)
avatar on Thu, 03 April 2014 12:11pm
img 22 is missing
Nilupul Perera on Sat, 23 November 2013 4:38am
It is very useful. I am 3d loving Neurologist in Sri Lanka. Hope to see more articles from you. Thank you soooooo much.
Samtherocker on Fri, 04 January 2013 6:27pm
Thanks for sharing this helpful information with us...You are the master!!
Issac on Fri, 17 August 2012 3:40pm
Thank you very much. Simple and Super. Very Informative .
Nana Ofosu-Osei on Thu, 26 April 2012 1:12pm
Thank you so much fro this excellent Tutorial. I understand so much more now.
Raja Haroon on Mon, 02 January 2012 6:40am
Great Information, i think you have to make a video Tutorials about that.
Rees on Fri, 25 November 2011 12:51pm
Quite valuable tip I would say, not sure how that gonna translate into the reflection mapping, I don't use specular mapping anymore hehe, will test it & see.
Vitaly on Mon, 16 May 2011 1:50pm
Thank you very much, Pedro! The marvellous info. Waiting for new tutorials!
Meysam on Tue, 14 December 2010 11:19am
so good dude . scientific and easy to understand . thank you .
Wayne on Mon, 06 December 2010 11:52am
Thanks a loooooot!!really useful for me!!
St on Fri, 26 November 2010 7:17pm
Informative! Thanks for sharing.
Ricardo Duarte on Thu, 25 November 2010 6:08pm
Great work!!! Congratulations...from Brasil! (with S!)
Mu¡rcio Siviero on Thu, 25 November 2010 11:20am
Congratulations!!! Very nice!!!
Matifou on Sat, 20 November 2010 9:52pm
Great tutorial! Thank you!
Usman on Fri, 19 November 2010 10:45pm
WOW really I dont have words to thank you for this really really awesome.
Hynol on Fri, 19 November 2010 9:12pm
As I understand, velvet is conductor? ;) Also I don't quite understand why you are using color map for specular highlights in dielectric - it is mistake - using desaturated image is correct method.
Mr.T on Fri, 19 November 2010 3:53pm
Amazing tutorial, thanks for your time.
Munkybutt's Avatar
Thrillhouse900 (Forums) on Fri, 19 November 2010 3:10pm
Unreal tutorial, such valuable information!Thank you!!
Graham on Thu, 18 November 2010 11:32pm
Simple and concise break down of the science of specularity Pedro! I have been studying 3d for a few years now, and I have been struggling to understand how to properly use color in my specular maps. This tutorial has finally cleared up many of the misconceptions I`ve encountered and has given me a more solid understanding of how specular reflections work in reality. I thank you so much!
Tairo on Thu, 18 November 2010 7:05pm
Very cool tutorial, i was at the original lecture in CCAA, it was very interting. one of Brazilians best 3D Artists there is.
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