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How To Add Ambient Occlusion with VRayDirt For PhotoRealistic Materials

Ambient Occlusion Map

Hey VRay users, today I’ll be discussing how you can use the Ambient Occlusion map VRayDirt to enhance your images. Ambient Occlusion, or AO for short, is an old rendering technique used as an approximation for true global illumination. Back in the day, when calculating GI used to be highly CPU intensive, ambient occlusion was developed as its cheaper alternative.

To put it simply, AO can simulate an ambient global lighting without actually calculating too many light paths. Imagine a completely cloudy day, and you’ll notice that light seems to be coming from all over the sky equally. Wherever objects are close to each other, they occlude (block) light, and all corners become darker. This is just like calculating GI from the sky without any direct light.

AO can achieve this same look faster, by simply calculating where objects or faces intersect each other, and making these corners darker.

AO has dropped out of use nowadays because calculating GI has become fairly easy for modern day processors. But actually, you can still use it to attain even greater realism combined with GI. There are two ways AO can help you:

  1. Add realistic grunge and dirt effects to corners and crevices, hence now named as VRayDirt.
  2. Bring out tiny details in the scene earlier lost by too much bounced lighting. Also, darkening of corners provides clean follow lines for the viewer.


So let’s get going and look at the nuts and bolts of the VRayDirt map in 3ds Max.


Basic Controls

  1. Radius – This distance sets the boundary for the AO effect from the corner. You can precisely control where the AO is applied within the radius by using a black/white texture. VRayDirt multiplies this texture with the radius value. Black areas get 0.0 radius, while white areas have a 1.0 radius value. Procedural textures like noise and cellular maps work quite well.
  2. Occluded Color – AO shadows are usually black in color, but using this parameter you can choose any color or texture you’d like. You can use a processed or darker version of the base texture here.
  3. Unoccluded Color – This sets the base color or texture for the object, or the same input you’d use in the diffuse slot of your material.
  4. Distribution – The higher the distribution value, the tighter and compact the AO effect will look. In other words, the dirt effect gets even closer to the contact edges.
  5. Falloff – Similar in appearance to the above distribution setting, this value controls how quickly the effect falls off the further it gets from the contact edges.
  6. Subdivs – If you’re not using any Global subdivs control in the VRay Render Settings, this parameter directly controls the quality of the AO effect. Increase the subdivs to remove graininess.


Advanced Features

  1. Bias – You can push the AO effect towards any direction (X, Y or Z) by increasing the bias. Biasing the AO in the downward Z direction can help in creating a rain stained effect on objects.
  2. Ignore for GI – This simply toggles the visibility of the VRayDirt AO effect during the GI calculation phase while rendering.
  3. Consider Same Object Only – When On, the AO will not be calculated for any other objects or surfaces. This means that whatever surface or object that is in contact with our VRayDirt object, will be excluded from this effect.
  4. Invert Normal – This setting will apply the AO effect to all the open corners of the objects as well. This is a great way of adding realistic wear and tear or paint peel-off to the edges.
  5. Work with Transparency – If you’re getting unnatural artifacts around transparent materials, opacity masked objects or invisible VRay lights, you should use this option.
  6. Environment Occlusion – This setting enables the use of the environment to calculate AO for objects not being directly occluded.
  7. Mode – You can choose either Ambient or Reflection Occlusion. Ambient method shoots rays in all directions equally, while reflection shoots rays depending on the viewing direction.
  8. Reflection Glossiness – Controls the spread of the rays traced for reflection occlusion.
  9. Affect Reflection Elements – When enabled, the ambient reflection will affect the reflection render elements. This can be used to create a reflection mask.
  10. Exclude – Simply choose the objects with this material that you want to exclude from AO calculation.
  11. Result Affect – Choose the list of objects which will affect the VRayDirt map calculation.


So this is all you need to know to get great results with VrayDirt. Don’t forget to share and comment. Wish you the best. Talk to you soon.

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