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Fasten Your Seatbelts; It's Going To Be a Bumpy NightDisplacement and bump mapping in Adobe After Effects
"Bump Mapping" and "Displacement Mapping" are terms used to describe the process by which one layer changes the appearance of pixels on another layer. In 3D terminology, the two are held distinctly apart for good reason.
"Bump" is the APPEARANCE of changing the surface of the geometry in a 3D model. The bump map is an image that describes high, low and intermediate areas and creates the illusion of surface variation by projecting specular light and shadow.
"Displacement" is the PHYSICAL change in the geometry by an image. In 3D, the model's polygonal shape is actually altered by the areas described by the displacing image.
In AE, however, DISPLACEMENT MAPPING was introduced before 3D geometry was even possible, probably as an aid due to the absence of 3D capabilities. Regardless of its origin, it's still alive and well today, and still continues to serve as an interesting plugin, albeit 2D only.
Displacement mapping in After Effects, although sharing the same name, doesn't actually change the surface of the layer (wait for it...). Today, in the latest 5.5.1 you still have it as a 2D effect only, mapping the pixels of the displaced layer horizontally and vertically ACROSS THE SURFACE OF THE LAYER without depth. So, for the 3Ders out there, it's a BUMP map that DISPLACES pixels along x and y.
So, while you're able to create some interesting looking ripples, don't expect to tilt the camera and see the echos of a shockwave peaking across the surface of your comp. After Effect's Displacement is AN ILLUSION of depth only.
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