Tips and Techniques/Natural Phenomena/Translucency
From VFXPedia
Translucency becomes especially important when you integrate thin objects like cloth, paper, petals or leaves into an environment with bright elements (sky, windows, lamps and so on).
To simulate it, you will need either a Camera Normals pass or an Incidence pass.
- So, you've merged the thin object over the background plate, but it looks too solid...
- Let's fix the bastard!
- Now make a branch from your background and merge it over the foreground layer before it's merged over the background. Set the Operator parameter of the Merge to Atop.
- The foreground object becomes invisible, huh? But look at these nice thin clouds generated with Fusion's particle system!
- Apply either the inverted Incidence or the Z Camera Normal channel to this new Merge2 as a mask.
- Now you can see, that only the surfaces which are facing the camera remain transparent whilst the surfaces looking to the side are more opaque.
- Reduce the Blend parameter of the Merge2. It still looks like simple transparency.
- To make the light coming through the object more diffuse, add a Blur tool between the background and the Merge2.
- To exaggerate the translucency caused by bright elements of the background, insert a LumaKeyer right before the Blur.
- This should already look nice. You may want to apply a gamma correction with a BrightnessContrast tool to the mask (Incidence or Z Normal) to alter the distribution of translucency depending on the surface angle.
- The thinner is the object, the more uniform is the effect. Thicker objects will have such translucency mostly on the parts oriented directly to the camera.
- Probably, you notice a dark contour on the edges of the object, especially if it's motion-blurred. This happens because the edges of the mask fade to black in the areas where the masking still has to be 100%.
To fix it, divide the mask channel (Incidence or Z Normal) color by the Alpha. This will extend the mask edges to the point when it covers the complete foreground object area.
- Of course, it's always a good idea to name the nodes according to their designation to not get confused having opened the comp in a three month time!
