Displacement Filter in After Effects
Two of the less well known features of After Effects’ Production Bundle are the Time Displacement Filter and the Displacement Filter. Both use the values of one image to affect the target image. In this tutorial, Philip Hodgetts first looks at the affect of the Displacement Filter first, then moves on to Time Displacement before discussing a source of gradient images suitable for Displacement and Time Displacement Mapping.
The Displacement Filter (Filters/Distortion/Displacement) uses values of Brightness (Luminance); Red, Green or Blue Channel, or combinations of channels to displace, or move, the pixels of the target image. All Displacement mapping is based on Brightness values, even if derived from only one of the color channels. Depending on the options in the settings, Displacement mapping pushes pixels that are lighter, further. The higher the value in the source image, the further the pixels of the target image are displaced.
With a radial gradient, text that is mapped to the gradient will distort following the shape of the gradient. In this example, as the text moves across the gradient, it will distort as if flowing down into the ‘dish’ caused by the displacement map, across the bottom and back up the other side.
These types of Displacement Maps are exceptionally useful for creating ‘flowing text’ effects where text flows down across an image in a sensual or smooth way, often reflecting the shape of the underlying image.
To make text flow across an implied curve in the underlying image, a Bitmap image program (such as Adobe Photoshop or Pinnacle Commotion) would be used to create a gradient that lines up with the ‘curved’ part of the target image. An exported reference video frame or Clip is useful for lining up the gradient and original image. If the image pans or zooms, the gradient may need to be animated in After Effects first as a pre-composition or created frame by frame in Commotion. (The Displacement Filter uses the displacement layer ‘untouched’ – any zoom, scale or filter applied to the Displacement layer will not be used unless the displacement layer has been pre-composed first.)
Once the gradient is created all that is required is to bring it into the same composition as the Target layer (or pre-compose if animation of the displacement layer is required) and choose it in the Displacement Layer pop-up in the Displacement Filter settings.
Displacement mapping can be used for items as simple as texturizing a layer (although the Texturize Filter will also achieve that outcome), or for providing pseudo depth to an image. Displacement Mapping can be used to distort an image so different parts of the image appear to be at different levels, even at angles if gradients within grayscale levels are used. An image can be used as its own displacement layer (the default) with interesting, if not terribly controllable, results.
The amount of displacement can be set independently for Horizontal and Vertical directions and the amount of displacement for each direction can each be derived from a different color channel source. For example, the red channel displacing vertically and Green controlling Horizontal displacement.
Displacement Maps can also be generated within After Effects using the ‘Ramp’ filter and pre-composing the layer although these Displacement Maps will be limited to linear and radial displacements.