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## Introduction

I originally made this tutorial for a lecture I gave at CCAA, a school in Brazil where I help to run the Post-Graduation course in Game Art. It came from the need to explain some elements of the materials that are commonly misunderstood. Especially about Specular maps which, sometimes, seem to be a bit confusing for some people.

Most artists, in general, have a pretty good understanding of Diffuse, Normal and Alpha maps, but it's often on the Specular map that they will get lost and sometimes even ruin a pretty good asset.

I hope you enjoy this tutorial.

If the shape of an object, in 3D, is the result of its geometry, the material from which this object is made of is the result of its shader and textures. Shaders are instructions that tell the render how an object should be displayed. Textures are images that provide visual information to the shader. They can be extracted from real life photographs, they can be digital paintings, or even procedurally generated (Fig.01).

Fig. 01

In this way, we use textures as inputs of a shader, defining attributes such as color, reflectivity, transparency, roughness, brightness and other characteristics of a possible material. Out of these textures, the most common are:

• Diffuse
• Specular (and Specular Power - aka Glossiness)
• Normals
• Alpha
• Self-Illumination

Normals Maps will change the normals of a given surface. They will make the light bounce off the surface as if it had hit something other than just the polygons.

Alpha Maps define transparency. It can be on materials such as water, glass, fire, smoke... Or it can also be used for creating different silhouettes, gaps and rips on simple surfaces (Fig.02).

Fig. 02

So, in some ways, if we disregard the truly transparent or translucent materials, like glass, where the transparency is at the core nature of the material, it would be ok to say that Alpha and Normal maps alter how we see the shape of an object more than the material itself.

Self-Illumination or Glow only defines parts of the object that emits light; that glow in the dark (Fig.03). Thus, transparency, embossing and brightness are material characteristics conferred by the respective use of the following maps: Alpha, Normals and Self-Illumination.

Fig. 03

But what about all the other aspects? Those that really define the nature of a material. Is it light or dark? Smooth or rough? Clean or dirty? Reflective or matte? It is made of metal, clay, wood or plastic? Is it wet or dry? Rusty? Stained? Scratched? Old and worn, or brand new? All these variables, and many more, are controlled by two maps: Diffuse and Specular (well, maybe three maps, since there's still the Specular Power. But because this one only affects the specularity, I'll consider it as part of the Specular slot).

But what are they? Everyone who works with 3D has at least a basic understanding that Diffuse is the color of an object and Specular is the light reflected on its surface... the highlights. But this definition is somewhat simplistic. We must remember that everything we see around us in the world is only visible because they are reflecting light. In essence, everything we see, if it doesn't emit light, reflects light (Fig.04).

Fig. 04

As in this example, the light-bulb will emit light in all directions and some of these rays will hit the teapot. The teapot will absorb part of the rays, in this case mostly the blues and greens, and bounce off the reds. Some of these bounced rays will pass through our pupils hitting our retinas, and this information will be sent to our brain so we can finally "see" the teapot.

The thing is, there are two ways this reflection may happen:

Diffuse reflection is a type of reflection where the light is reflected from the surface at multiple different angles (Fig.05).

Fig. 05

## continued on next page >

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Cr@chrisrush.net 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.
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.