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Brief Consideration About Materials

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Date Added: 30th December 2010

Look at the following example (Fig.19). This is the diffuse texture.

Fig. 19

And here is the specular map (Fig.20).

Fig. 20

Notice that the ones on the left are respecting the true nature of the materials, with the wood (dielectric) using the inverse color of the diffuse, and the metal (conductor) with same colors of the diffuse. It has some scratches and a little more contrast, but it's still very similar to the diffuse in terms of hue.

The ones on the right are not good, they are just wrong. Wood specular matching the wood diffuse, metal specular with inverse color.

Now, if you put them on layers like in Fig.21, with the diffuse on top of all the layers of the specular file, and set to Linear Dodge, then the result you get is this (Fig.22).

Fig. 21


This result will never look very good because it's like having the specular reflection on top of everything, as if there were several different light sources illuminating the surface from all possible angles. But you can already feel that the reflections on the left look more natural than the ones on the right.

Now, let's make this a little more interesting. What about having a preview like this one here, in Photoshop (Fig.23)?

Fig. 23

To do that is actually quite simple. Below the diffuse layer, in Photoshop, create a group and make it Multiply. In this group add two new layers. The bottom one you will fill with black. On the top one you will create some white spots, faking the shape of the specular reflection that you would expect to see on the surface (Fig.24).

Now, you just need to drag the spots around to see how the specular reflection works for this material (see Fig.23).

Pretty cool, right? Of course, I don't keep these layers visible all the time while working on the specular texture. Sometimes I just don't use them at all. But every time I want to be sure I'm heading in the right direction I'll toggle them on and off, and move the small white spot around, to see if I'm still on track.

You may be curious about skin reflection. After all, a good skin reflection will be hued as a dielectric material (inverse of the diffuse color), but our skin does conduct electricity. Yeah, this is true. But our skin is a far more complex material, with several different layers and elements - epidermis, fat, oils, muscle, tinny hairs, sweat, salt, etc. Maybe the mix of these different elements results in a dielectric look, or maybe because oils are not conductive of electricity, and they are on top of all layers of the skin, the final appearance is dielectric... I don't know really (hey, I said this is not a science study!) But it's true, if you are trying to make a specular map for skin, you should start with the inverse hue of the diffuse.

That's it - I hope you found this tutorial useful! There are some other things you could do in order to make this preview of the specular reflection even more interesting, but I'll leave it for a next tutorial.

Fig. 24

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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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