Blender 2.8 | Cycles Render
The shading normal‘s Z component can be easily used as a ready-to-use procedural mask for ‘covering effects’ like dust, snow, and if baked, also as a base for particle effects like debris and vegetation.
This simple shading flow example the shading normal‘s Z component, that represents how much the surface is facing upwards is separated , mixed (multiplied) with a noise textured and than fed into a ColorRamp Converter node for fine tuning the resulting mask:
This is the full shading flow of the snow effect in the image above:
After Effects CC 2019
Adobe After Effects has a very effective Camera Lens Blur effect that is capable of efficiently faking DOF (Depth Of Field) and Bokeh visual effects for 3D rendered images and animations, and also animate a fake “Focus-Pull”.
The effect will work best on 32 bit float EXR files, and requires a Z depth render element (pass/AOV) to be rendered with the main RGB image, and supplied as the Blur Map layer.
If necessary, color correct the Z depth image so that the Black to White range will reflect the wanted focus range, and that the closest depth will be Black, blending into White at the furthest depth.
Example of a Z Depth image:
Controls the blurriness
Choose the lens iris shape (number of blades) to design the Bokeh effect
Defines a black & White Depth Layer (Z Depth) where black is the closes point to the camera and white is the furthest.
Blur Focal Distance:
Values of 0.0 to 1.0 will have the black through grey to white areas of the Blur Map remain at focus (sharp)
Highlight > Gain:
Intensify the highlights to create a more dominant Bokeh effect
DOF in Arnold for Maya