Vray Materials Part 3 – Reflections

5 01 2012

So, as I tend to start my posts, I must apologize for not being as timely and frequent as I’d like, but none the less here you are, so you either 1) forgive me or 2) just found this site and therefore haven’t been diappointed…yet.  🙂

Let me also say that I have downloaded the new Beta version of Vray for Rhino and therefore my User Interface may or may not look like what you have, but rest assured, the content of the tutorial is still the same.  I will try my best to clarify the reflection layer and the refraction layer, what each is used for and how they work well in combination WITHOUT getting too nerdy and stuck in the physics behind the way things work.

Reflection and Refraction:

What are they and what’s the difference?

For those, like me, who haven’t taken a physics class in a number of years, let’s review what a reflection is and how it’s different that refraction.  It’s important to remember that both reflection and refraction have to do with the way that light reacts to a material.  Reflection deals with the way that light bounces off of the material while refraction deals with the way that a material passes through a material.

I have created a small diagram below that explains how when looking at reflection, the light wave comes from the light source and makes contact with the front face of the material at a given angle.  This is known as the angle of incidence.  The light wave then bounces off the material at the exact same angle, known as the angle of reflection.  Going back to my high school physics class, the angle of incidence is equal to the angle of reflection.

Refraction on the other hand is the way that that the light wave travels through the material.  Because the material has a thickness and a density, the light wave is refracted in the thickness of the material as it bounces off of the “stuff” in the material.  The angle of the light coming out of the material isn’t the same as the angle of the light entering the material.  This difference is measured by the Index of Refraction (IOR).  This is the EXACT reason that when you put something in a pool, the object appears to bend.  The IOR of air in a vacuum is 1.0 (meaning the angle is the same coming in the material as exiting the material).  As the IOR number increases, the more refraction occurs.  To see a list of the IOR of various material, google it or check out http://en.wikipedia.org/wiki/List_of_refractive_indices.

Reflection Layer:

The reflection layer controls the amount that a material reflects the surround scene.  This goes anywhere from a mirror like surface to a much more subtle reflection off of a hand railing, glass on a table, or piece of plastic.  it is important to think of the reflection layer as dealing with simply the REFLECTIONS of that material, regardless of the transparency, etc.

To add a reflection to your material you will have to add a reflection layer to your material.  This will allow you to control many of the properties of the material’s reflection.  To do this, create a new material and rename it appropriately.  Then right click the name of the material and a new pop-up menu will give you many options.  You want to select the “Create Layer” and then “Reflection”.  When this is done, you will see under the material name you now have both a reflection layer and a diffuse layer.

Once this is done, you can click the “Preview” to update the material and see that now the material has a bit of reflectivity to it.  You are seeing the light and the checker pattern from the ground on the material.  Also, notice that on the right side, we have a Reflection layer under which there are a lot of controls that will affect the reflectivity of the material.

Applying this reflective material to the existing scene, we can give it a quick render to use as a baseline for some of the upcoming changes we will make.  Below you will see my initial render:

Reflection Map:

The first parameter that we will look at working with is the Reflection Map.  Looking at the Reflection layer, we can tell that by default a reflection map is already been placed because there is a capital letter “M” next to Reflection.

When you select this Map, you will notice that the Texture Editor opens and by default the Fresnel map is applied.  A Fresnel map varies the amount of reflection based on the viewing angle.  This is why the edges of the preview sphere seem to give the material that distortion, that we as humans come to expect from a reflective sphere.  Let’s take a look at some of the options that we can control through the texture editor.  First we’ll look at the Perpendicular and Parallel colors.  **Please note that Perpendicular and Parallel are the omenclature with the new Vray for Rhino version 2.0 Beta.  Previous versions of Vray for Rhino used the names “Fresnel Color and Refract Color”**

I’m going to use the preview sphere to test out how these changes will affect our material.  So as you can see below, by changing the Perpendicular color, the color of the reflection will change.

In a streak of honesty, I must fully disclose that I sorta understand what changing the Parallel color does, but certainly not well enough to explain how it works and affects the material as I have always left this value at black.  I have however run a similar test to that above.  See below for a test with the Parallel color at Black, and then changing it to yellow.

Now that we understand what these parameters do, we can adjust them when we are looking to get away from the mirror/chrome look and attempting to give a bit more realism to our scene by adding color to our reflections.  The last parameter that we will explore under the Fresnel map is the IOR.  This number determines how reflective a material is.  To be technical (I know I tried to avoid being all physics nerd, but bear with me) As the Fresnel IOR (Index of Refaction) gets lower, the larger an angle is needed to have the material reflect.  A higher IOR means that a smaller angle is needed to create a reflection.  What’s that mean to you??  Take a look back at our previous reflection diagram:  A higher Fresnel IOR means that at a slight angle, I can see reflections.  At a lower IOR at the same angle, I might not see the material as reflective.  As previously mentioned, you can find many websites that give a close approximation for the IOR of various materials.  Lets’ try manipulating this parameter to allow some experimentation using our previous scene:

As an aside, I know I didn’t tell you what the Refract IOR does here, but if I never change the Parallel (Refract) Color, you really think I have the foggiest clue what the Refract IOR does here??

Filter Color:

Very quickly and simply, the filter color changes the color of the overall reflection.  If I want all my reflections to appear red, I’ll change the filter color from white to red.  The amount that this color is taken on in the reflection is directly correlated to the strength of the reflections.  This is similar to how the Perpendicular Color works, but see below to see the difference between the two.

Reflection Glossiness:

The Glossiness parameters allow you to control how the reflections look as they are being reflected off of a material.  Think about some of the highly reflective materials that you have run into over the last 24 hours.  You woke up this morning and presumably brushed your teeth, spitting your toothpaste into a highly reflective porcelain sink, looking up in the highly reflective mirror to ensure your hair was perfectly in place before grabbing your stainless steel travel coffee cup before you headed out the door.  Before you made it out the door to work this morning you have already dealt with three very different levels of reflectivity that couldn’t be established with the previously discussed parameters alone.

The sink is a material that dissipates the reflection a bit because of the natural occurring scratches, dents, etc in the material.  The mirror gives seemingly accurate highly glossy reflections that nearly mimic the actual objects.

The stainless steel travel mug is a good example because it really depends on the type of mug that you have.  Mine for example is a brushed stainless, which means that it is much less glossy and doesn’t give the clear and highly articulate reflections that my wife’s, whose is closer to a mirror finish, does.

The control over the definition or articulation of a materials’s reflection due to it’s uneven nature (such as the brushes stainless) can be controlled with the Reflection Glossiness.  The amount of reflection glossiness is actually a two part equation that deals with the Highlight Glossiness number and the Reflection Glossiness number.  When these are both set at 1, the material will be mirror like.  As these numbers are reduced, the material’s reflections become much more blurry.  **Don’t reduce these numbers to below .5 because you will find HIGHLY increased render times and no sort of reflections)**

I am attaching a matrix from the Vray for Rhino Manual written by Chia Fu Chiang and Damien Alomar.  If you haven’t already, check out this manual, it’s a GREAT reference!  It can be found at the Chaosgroup website or Spot3d.com

Matrix part of Vray for Rhino Manual by Chia Fu Chiang and Damien Alomar

Coming up next:  Lesson 4 – Refraction Layer




5 responses

18 01 2012
Vray Materials Part 4 – Refractions « macdesignstudio

[…] I have gone through a brief explanation of the differences between reflection and refraction in my previous post.  But to review, refraction is the visual distortion that occurs as a result of a transparent or […]

19 12 2013
Vray Material Basic – 2 | berita dan informasi arsitektur

[…] ) Vray-materials-part-3-reflections […]

9 09 2016

is there a way to distort the reflexion?, (like a piece of steel that is not perfect plane)

9 09 2016

Yes, this could be as simple as using a bitmap in the reflection parameter. A noise map or something similar will add a bit of difference to the reflection and will add realism to your renderings. If you continue to struggle with this, let me know and I’ll try to add a tutorial on this.

14 09 2016

I did it and it worked very nice. Thank you,

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