Ambient Occlusion is an old deprecated feature replaced today by full global illumination. Even though it’s not used a lot nowadays, it’s still relevant in getting that photorealistic look.
Ambient Occlusion is the effect you get when light gets blocked to create dark corners in a scene. It is the same effect you get on an overcast day with the sky acting like a domed ambient light. Ambient Occlusion, or AO for short, is a cheaper way of simulating global illumination or even dirty corners. But now it can be used for fine tuning the darkness of the corners using Photoshop.
In this tutorial we’ll take a look at creating an ambient occlusion pass with a free plugin. You can download this plugin from here. There is a manual way getting the same render pass, but this render pass will make the job much easier.
Just drag and drop the extracted file over the 3ds Max interface. After being installed, you can find it in Main Menu > Tools > ml_plugins > VRay ambient occlusion.
VRay Ambient Occlusion
The plugin gives you two calculation methods to choose from. You can either calculate it as a Dirtmap or from a Skylight. The Dirtmap option essentially works by calculating AO from the proximity of all objects. The more the objects are closer to each other, the darker the AO. You can set the radius for the extent of this dirt falloff. This works like VRay’s own VRayDirt map.
The Skylight option is more realistic but also more time intensive than Dirtmap. The Skylight options further let you set a fully spherical or hemispherical dome as light source. This is more akin to a true global illumination calculation.
Furthermore by setting the quality subdivs option you can control the noise in the AO pass.
But before you press ‘Render’ you’ll probably need to set the ISO for the camera way up high. This is because we’re working with Gamma 2.2 and the AO pass will come out dark. In this example the ISO has been changed from 200 to 1000. Also, if you’ve got glass windows and objects in the scene, then these should be hidden. Glass objects don’t receive AO effect, and the result will look odd in the final image.
Just provide a Save Destination in the Common Render settings, and press ‘Render’ in the plugin window.
Import the AO render pass over the RGB pass in Photoshop. Set its Blending Mode to Multiply. This will only add the dark portions of the AO pass to the RGB pass. Now we’ll also need to color correct the AO pass to better fit the image.
A Color Balance adjustment has been applied here with boosted red and yellow midtones. Next a Levels adjustment helps in increasing the contrast of the AO layer.
Finally, we can now use the opacity slider for this layer and dial it down to below 50%. Remember we only want a subtle shadowing effect to match real life references. With such precise controls you can set the darkening of corners and get the look that you want.
In addition, if you wish to remove the effect from certain areas, you can mask them out with a grey or black brush.
So this was a quick tip for getting AO passes for compositing easily. Hope you found it helpful. Stick around for more useful tutorials on this blog. Remember to Share and Subscribe.