THE VFX MAP BAKING GUIDE: AMBIENT OCCLUSION

THE VFX MAP BAKING GUIDE: AMBIENT OCCLUSION

Paul H. Paulino’s latest article on auxiliary maps.

Paul H. Paulino allowed us to share his latest article on auxiliary maps. Useful tips and tricks for ZBrush, MARI, Mudbox and V-Ray. 

In this series of articles, I’m going to talk about auxiliary maps and how you can use them in your VFX texturing and shading workflow. Keep in mind that these techniques I’m going to showcase are mainly focused on assets with multi tiles UV’s (UDIM). These concepts might not apply to a game pipeline.

In this article I’m going to share five different ways you can extract your Ambient Occlusion map (aka AO) and I’ll also demonstrate a simple technique in MARI to use your Ambient Occlusion to create interesting Dust/Dirt masks. I’ll give you a step-by-step tutorial and also highlight PROS and CONS of each technique based on the final quality of the map and the time it took to extract. This way you can choose the option that fits your purpose.

Again, keep in mind that this is my personal experience and these are the software that I had the opportunity to work with in the past year and a half that I’ve been working in the VFX industry.

WHAT IS AND WHY DO I NEED AN AMBIENT OCCLUSION MAP?

We often call these maps Auxiliary Maps for an obvious reason: they are going to assist us during our texturing/shading process. I don’t want to get crazy technical here, so I’m going to share with you this quote from Wikipedia on AO: attempts to approximate the way light radiates in real life, especially off what are normally considered non-reflective surfaces”

Here you can see how does an AO map look like. As you can see, the occluded areas are fading into black, and the unoccluded areas are white. The inverted version of the maps will be extremely handy for us in the future and you’re going to understand why.

As a texture painter, usually the map baking process is our first step as soon as we have approved UV’s and model. This process might take a while depending on how large, how many UV tiles and also the resolution you’re baking your maps.

BAKING AO VS PROCEDURAL AO

In this article, I’m going to focus on how you can extract maps from your models so you can use it anywhere (MARI, Photoshop, Substance, etc.), but you can also use procedural Ambient Occlusion nodes using software such as V-ray and Arnold. One thing you might consider if you working on shaders for VFX: using AO procedural nodes can slow down your render times considerably, so keep that in mind. It works well for still images, but if you are going to render something in movement, it might be better to use baked maps.

PREPARING YOUR OBJECT

Before we jump into the baking process, I would like to highlight a few steps that you should consider. 

  • If you are dealing with an asset which is excessively high poly, it will be a better idea to break it down into pieces and bake the AO separately. Since we are going to need a subdivided model, this step is critical.
  • The another important thing to consider is the quality of your UV’s. If they aren’t unwrapped properly and have distortion in some areas, your maps are going to reflect that. So keep that in mind before jumping into the baking process. I recently wrote an article giving UV tips. You can check it out here.
  • To get a clean and smooth AO map in all the methods below, we will need to subdivide our mesh a few times. Usually having our mesh with a range of 4 million – 10 million polygons is good enough. If you’re getting more than that with your whole object, you might consider breaking that into pieces as I said previously.

BAKING METHODS

PROS
  • If you’re going be painting in MARI, it gives an exporting to change the extension to UDIM.
  • Variety of options
  • Insanely Fast
CONS
  • Settings can be confusing and give you an unclean map.

BAKING TIME

  • Machine Specs: i7 6700K | 32 GB | Geforce 1070
  • Tile Resolution and Quantity: 2K – 4 Tiles
  • Baking time: Aprox. 2 minutes 

STEP 01

Import your mesh into Zbrush. Make sure to have it with enough subdivisions (4 million polys or more)

STEP 02

Go to Zplugin > Multi-Map Exporter.
On the screenshot below I highlighted the areas that you should pay more attention while adjusting your settings.

  1. Check the Ambient Occlusion Option
  2. Select the desired resolution
  3. Click on File Names and choose your UV tile ID format
  4. Here you can find the main settings for your Ambient Occlusion. The settings above are the ones I usually use, but it takes a lot of trial and error. Below you can see the information from the Zbrush Documentation website

Occlusion Intensity: This slider increases the Ambient Occlusion Intensity making the ambient occlusion areas larger and darker.

ScanDist: Scan Distance increases the distance of the secondary color in the Ambient Occlusion.

Aperture: Aperture affects the scale of the Ambient Occlusion, with smaller values giving a softer affect.

STEP 03

After adjusting the settings, just click on Create all maps. 
Here’s the Zbrush AO map preview in MARI.

Guides for other tools

HOW TO USE AN AMBIENT OCCLUSION MAP?

Now that we know several methods to extract our Ambient Occlusion Map, how are we going to use it?
On the video below, I showcase a quick technique that I’ve been using quite a lot on my personal work. It might look simple, but if you understand the principle, you will be able to achieve incredible results without too much effort. 

And that’s not the only way to use Ambient Occlusion maps. You can be creative with this map and use it to enhance your diffuse and specular maps. Or maybe use it on your bump to erase some areas and get a more organic look.

Paul H. Paulino, VFX artist 

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    THE VFX MAP BAKING GUIDE: AMBIENT OCCLUSION