3D Artist
Sep
25

How to create a quick ambient occlusion pass

Tips & Tutorials
by
stephen.holmes

This week we’re going to look at a quick method for achieving an AO pass in LightWave

Thanks go out to Ben Cooper for this tutorial. See more of his work at www.bencooper.yolasite.com.

How to create a quick ambient occlusion pass

 

01 Create an occlusion node 

With the character object selected in LightWave Layout, we F5 to open the surface editor. Select the surface to which you would like to add the occlusion shader, which in this case is called ‘Dragon body’. Click on the ‘Edit nodes’ button – this will open up the node network window. Click on ‘Add Node’ in the top-left corner, and follow the drop-down list to the ‘Shaders’ option. Follow through to ‘Diffuse’, and then select the Occlusion II shader.

How to create a quick ambient occlusion pass

 

02 Add to the surface

Next, click and drag on the red dot next to ‘Color’ on the Occlusion II shader. Connect the line to the ‘Diffuse Shading’ channel. This will override the surface with the Occlusion Shader and enable the surface to behave the way we need it to. There are other ways to apply AO in LightWave 3D, but this is the way I prefer based on the look that this particular shader can produce for our AO pass.

How to create a quick ambient occlusion pass

 

03 Define scale

Now, double-click on the shader. Here, we are presented with a drop-down menu to specify the ‘mode’ in which we want to let the shader behave. For our purposes, I will be using the ‘Range’ mode. This will allow me to find the level of AO darkening that I am happy with for my image. The ‘Infinite’ mode doesn’t take the distance of objects between each other into consideration, and as a result can come out way too dark in some cases. This mode is also not advisable for interiors, as it can produce pure black results. I now repeat the first three steps of the tutorial on all the surfaces of the dragon.

How to create a quick ambient occlusion pass

 

04 Environment treatment 

Next, we need to make sure that for the AO pass we set the environment backdrop to pure white. This will assist us when we add the AO pass as a ‘multiply’ layer in our compositing package, as it will only take the dark parts of the layer and apply that over the colour image. It is also important to note that if you are working with a level of distance fog in your scene to include the distance fog on the AO, otherwise you will find when compositing your image that the AO is running over your fog, which won’t look right. Just be sure to set your fog colour to pure white for the AO pass.

How to create a quick ambient occlusion pass

 

05 Render settings

LightWave has gone to great lengths to ensure that the sampling part of the workflow is as simple and optimised as possible, resulting in many less test renders and tweaks to get a good clean result. By default, Shading samples are set to eight samples in the Render Globals. All we need to focus on is adding enough anti-aliasing to get a clean result. 8x AA should work fine for this character. Also, be sure to have Noise Reduction switched on in the Render Globals for that extra bit of polish on the AO. It could also result in having to use less anti-aliasing depending on your scene.

How to create a quick ambient occlusion pass

 

06 Add AO in your composite

Now, you can simply load your rendered out AO layer into your favourite compositing package and merge it to your colour layer with a ‘multiply’ method. Tweak the opacity of the AO until you are happy with how it sits. That’s how simple it can be to achieve an AO pass in LightWave 11.5. These steps are the basics that lay the foundation for dealing with even more complicated scenes. Fast and user-friendly techniques like this are always welcome in any animation pipeline.

How to create a quick ambient occlusion pass

 

Resolution considerations

In scenes that don’t have fine detail, a way to save on render time – especially if you are rendering an animation – is to half the size of the frame to that of the colour layer. This can save you hours of rendering time and produce a good looking final product. All you would need to do is to scale up the AO pass with a resize tool in your composite before multiplying it over your colour layer. Also, because it’s half the size, it means that in most cases you can get away with using half the amount of anti-aliasing of that which you used in your colour layer.