Time Displacement in After Effects
Like Displacement Mapping, Time Displacement uses the values of one image to manipulate the pixels of another image. Unlike Displacement Mapping, Time Displacement uses the values derived from the Displacement layer to select pixels from earlier or later in the layer. Time Displacement affects the image so that any mid-level value for a given pixel (50% brightness) tells After Effects to display the current frame for that pixel. A value lighter than 50% will cause the displayed pixel for that brightness value to come from later in the layer; a value darker than 50% will cause the displayed pixel for that value to come from earlier in the layer. Displacement values in between 50% and maximum or minimum will display pixel values that are closer or further away in time in the layer.
Let’s consider a simple example with 3 vertical bands: black at the left of screen, 50% gray in the middle and white for the right hand third.
With a maximum displacement of 1 second, the center band will display pixels from the current frame, the left hand, black band will display pixels from 1 second (maximum displacement) earlier in the layer, the right hand, white band will display pixels from 1 second ahead (later) in the same layer. If the there were grayscale values in between white, 50% and black then pixels from the frames in between the current frame and frames 1 second earlier or later in the layer.
Time Displacement works particularly well when there is a moving part of the image with a relatively static background. This combination shows up the time displacement on the moving part of the image, while the background stays ‘normal’ because there is not much variation on the layer over time.
Time Displacement is also great for creating all sorts of distortion field and ‘transporter’ style appear or disappear transitions.
Displacement Gradients can be created in any Bitmap or Paint Program such as Photoshop, Painter, Xres, among others. Custom gradients for a particular image need to be created for that Project but a great source of Gradients for Gradient Wipes, Displacement Maps or for Time Displacement are available in the Video Spice Rack collection of some 300 plus PICT and TIFF format grayscale gradients. There are sample Spice Gradients at <http://www.pixelan.com> and for the small investment, the Video Spice Rack is an excellent addition to any toolbox.