Go beyond Ambient Occlusion

Lesson by admin | Official 5SRW study material


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.

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Hey, this post is not to say that one technique is better than another, I just want to adopt my usual photographic approach to draw your own conclusions.

 

INTRODUCTION

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

mat-editor

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

 

PRACTICAL EXAMPLE OF ‘AO’

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

no-black-velvet

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

ao

 

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

post-production

Not bad, but we can go further!

 

PHOTOGRAPHER EYE

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

As real 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 grazing lights to highlight findings and imperfections: how come it 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 generated by first. Actrally 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.

bouce-lighting

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$ 😉

black-velvet

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”:

black-plane

 

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:

yes-black-velvet

Comparison:

comparison

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!

 

CONCLUSIONS

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 understand “Why?”

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

Happy render,
Ciro Sannino

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Notes

Lessons to know more: Lighting in 5-Step method

(1) 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

(2) 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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