Due to both latency and imperfections in the prediction process, a last-moment adjustment might be needed before the frame is scanned out to the display. This is called post-rendering image warp  (it has also been rediscovered and called time warp and asynchronous reprojection in the recent VR industry). At this stage, there is no time to perform complicated shading operations; therefore, a simple transformation is made to the image.
Suppose that an image has been rasterized for a particular viewpoint, expressed by position and orientation given by yaw, pitch, and roll . What would be different about the image if it were rasterized for a nearby viewpoint? Based on the degrees of freedom for viewpoints, there are six types of adjustments; see Figure 7.19. Each one of these has a direction that is not specified in the figure. For example, if is positive, which corresponds to a small, counterclockwise yaw of the viewpoint, then the image is shifted horizontally to the right.
Figure 7.20 shows some examples of the image warp. Most cases require the rendered image to be larger than the targeted display; otherwise, there will be no data to shift into the warped image; see Figure 7.20(d). If this ever happens, then it is perhaps best to repeat pixels from the rendered image edge, rather than turning them black .
Steven M LaValle 2016-12-31