Go beyond Ambient Occlusion

Lesson by Ciro Sannino | Official 5SRW study material

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LESSON – Ambient Occlusion

  • What is Ambient Occlusion
  • VRay Dirt and VRayExtraTex
  • Compose AO in post production
  • Apply photographic approach
  • Comparison


What is the Ambient Occlusion and how is it used? But most of all .. why?
In this lesson I will share with you some considerations about ambient occlusion and in parallel about light modeling, in the field of photographic renders.



First, for those not familiar, Ambient Occlusion is « attempts to approximate the way light radiates in real life, especially off what are normally considered non-reflective surfaces » – Wikipedia

So the Ambient Occlusion (from now on I’ll simply call AO) throws shadows Environmental linked to the proximity of objects and – above all – is not linked in any way to the light present in the scene. So much so that it can also be generated by turning off all the lights and global illumination.

The implementation in V-Ray is really very simple(1). Go to tab ‘Render Elements’ and:

  1. Click ADD and select from the list ‘VRayExtraTex
  2. Put VRayDirt as Texture
  3. Create an instance in the Mat Editor
  4. Edit the radius to define the occlusion


To tell the truth already 1-2 points often enough, the default radius is 25cm which in most cases is more than good (2).



The image below is the typical situation in which the AO could be useful to highlight details:


The details of the door are not so obvious, then creating the AO version of the same shot:



We can superimpose in Photoshop in Multiply mode and – 20% opacity, with a satisfactory result. I keep just 20% to avoid fake look:


Not bad, but we can go further!



Returning to the original image when the door seems to lack body, we can do a completely different analysis.

Thinking as a photographer I’m amazed by how it is possible that an oblique light fails to bring out the details?! It ‘really strange, a photographer is accustomed to use sidelights to highlight imperfections: why this does not happen in this case?

Maybe it happens, but the ambient light that comes from the left crosses another light crosses from the right. This light from right ‘off’ the shadows! Actually it isn’t a real light source: it is the light that bounces off the walls and ceiling, which, being completely white and clean return an equally strong light that ‘clears’ the three-dimensionality.


Please note: this issue is not about V-Ray and 3ds Max, but is purely photographic! It also happens in the real sets, so using draps of black velvet we can avoid unwanted light bounces. This is the “modeling light”, one of the most fascinating things that I know and effective! 🙂 cleaned and returned just as strong a light that ‘clears’ the three-dimensionality.

If you want you can buy a real black velvet drap on Ebay for 280$ 😉


Luckely, implement this concept in V-Ray is as easy…  and cheap!! Just create a plan or a volume and position them in front of the surfaces we want to stop their light bounce, associating a common material “total black”:



Here is the result: the light direction is clear, the picture is much more three-dimensional and above all in harmony with the light in this scene:




The differences are obvious:

BASIC: starting version
AO: ambient occlusion add details, but it is flat. Not consider the direction of the light. In fact, the shadow also goes to the left, where he would have no reason to exist
BLACK VELVET: with the black velvet details increase, according to the light direction!



Obviously I’m not against the AO 🙂

You should always know the tools and then make your own choices based on the situation . The real problem comes when you use the tools without thinking … just because on the forums, tutorials other people say so. Do not skip the real question and always try to yourself: “Why?”

The photography offers all the answers to the rendering world. You guys don’t need to be “superender heroes” to simply try and get success . Just use V-Ray as it were a real DSLR in your hands, taking a real photo.

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Download the 3ds Max file with all V-Ray settings to apply these concepts.
See with your eyes the photographic approach:

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(1) Lessons to study 5SRW and lighting in 5-Step method

(2) The AO can also be activated from the render setup, but in that case is ” embedded ” in the rendering. Personally I prefer to have two separate layers to control them more easily in Photoshop

(3) Another thing you might have to edit the ‘subdivision’ – Anywasy 8 often is good because it will be used in photoshop always a 20-30 % maximum opacity.

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