3D Rendering

In this tutorial we will go through the process of creating realistic wet materials. Although the tutorial is written for max and vray users, the same workflow can be adapted to any software you may use.

1) Analyzing the reference
In order to re-create any type of material the first and most important thing is to look at real photos of what you are trying to replicate in your rendering, and really understand what is happening there.

For example, take a close look at the photo bellow.

Not only the asphalt is quite reflective because of the layer of water on it, but also the glossiness/specular varies a lot across the image. In areas where the layer of water is thicker the reflections are a lot sharper and the bump of the asphalt is less present. In other areas, where the asphalt is dryer, the reflections become glossy and they are also distorted by the bumps on the street.

2) Replicating the effect with 3ds max tools and vray.
To sum it up, in order to create a wet asphalt shader we need a diffuse map, a bump map, a reflection map and most importantly a map for the glossiness chanel.
Open the “wet materials scene” that you find in this zip file.

Although all the maps are already there, they are not activated yet; we will activate them one by one to better understand how each of them affects the overall look.

a)    The reflection map

For the reflection, I have used a falloff with 2 maps (basically a darker version and a lighter version), for more control. Besides the brightness both maps are identical.
The areas close to the edges (where I want the layer of water to be thicker) are whiter and more uniform, while other areas are darker and noisy.

Activate the reflection map by clicking the checkbox next to it in the maps rollout.
If you hit render, at this stage you will end up with something like this:

b)    The bump map
If you activate the map and hit render you will notice that the reflections are distorted in the areas where the map has noise applied. Again, in other areas where there is more water, you need to paint it with neutral gray, since there is no bumpiness.

c)    The reflection glossiness map
This one makes all the difference. Before activating it, the reflection, although distorted by the bump map in some place is still very sharp an unnatural. As we have noticed from the reference image at the beginning of the tutorial, this should vary across the image, depending again by the thickness of the layer of water. White causes the reflection to be sharp (equivalent to “1” from the glossiness parameter), while darker values make the reflection much more glossy.
If you hit a render after having activated it, you will end up with something like the following:

d)    The diffuse map.
Although not really important for the purpose of this tutorial, it has quite an impact on the realism of the image, so activate that as well and hit a final render.

If there is something you don’t understand or if you have any kind of questions, don’t hesitate to ask.

Hi guys,
Hopefully, in the following weeks I will have a little more spare time that I intend spend writing some new tutorials.
Bellow is a small list with what I intend to write about. I am hoping that you can come up with some more suggestions, so if you have any ideas feel free to post a comment.

Rendering liquids
Rendering wet materials
vray sss
How to setup a daylight interior illumination
Post processing an image from raw render to final output

I look forward to reading your suggestions.

Best regards,
Alex

In the next tutorial I will try to explain what parameters you need to control in order to obtain realistic caustic effects with 3ds max and vray.

Open the “caustics start” scene that you will find in this zip file.
As you can see, the glass material is already prepared:
-reflect 213:213:213 with fresnel reflections checked.
-refract 238:238:238
-IOR 1.44
-Affect shadows – checked

First, go to the “Vray: caustics” rollout and activate it by checking the box next to it.
If you render it at this stage you will end up with something like this:

The caustics effects are already visible but they have a fake look and lack definition.

The most important parameter that we need to adjust is the “caustics subdivisions” that are emitted by the light. For this, you need to right click on the direct light, choose vray properties and increase the “caustics subdivisions” from 1500 to 20000 and render it again.

The caustics are starting to look more real.
Now let’s see what other parameters do…

If we change the “search distance” parameter to 0.02 we will end up with something like following:

As it can easily be observed, smaller values produce much sharper caustics but a lot more noisy.
Higher values result in smoother caustic effects, but at the same time the higher the values, the blurrier they get.

After several tests, I am happy with a search distance value of 0.09 for this scene. The caustics still look a bit noisy, but we will try to adjust this by tweaking the “max density” parameter.

Max density is probably the trickiest parameter, and if you don’t understand how it really works, you can end up with unexpected and undesired results.

First, let’s do a test; increase the max density from “0” to “1” and look what happens:

Where did all the caustic effects go?
Take a look at the following diagrams:

If max density is greater than “0”, when vray needs to store a new photon, it will look if there is another photon within the radius specified by this parameter. If it finds one, it will just add the energy to the one in the map, in order to keep the photon map at a smaller size (case 2 of the diagram). If the area is too large the end result will look like there are no caustics in the rendering.
If no other photon is found within that radius, the new photon will be stored in the photon map (case 1 of the diagram).
After doing some tests, I think that a value of 0.002 works just fine for this scene.

In order to realize just how tricky this max density can be, leave it at 0.002 (that works fine at the moment, as seen in the rendering above) and increase the caustics subdivisions of the direct light to 50000 and run another test rendering.

You would expect better results, right? WRONG! The result looks exactly like the one with max density set to “1”. Basically by increasing the caustics subdivisions we ended up with more photons acting like “case 2” of the diagram.

Other parameters:
Multiplier – it makes the caustics brighter if increased, or less bright if a value lower than “1” is assigned to it. In theory you should leave it at “1” since it is supposed to give physically correct results.

Max photons – somewhat similar to “search distance”, but instead of using the distance between photons to interpolate, it uses a higher or a lower number of photons.

Mode – works almost like the irradiance map. You can choose “new map” to calculate it again, or you can save it once you are happy with it and load it later for further renderings.

Another important factor to keep in mind is that the looks of the caustics depend a lot on the geometry of the objects that cast them. For example if you want to render a swimming pool with caustics you need to model a realistic water surface (or at least a really good displacement map), otherwise it will not look natural.