RayTracingTAA Converging in Path Tracing requires a stationary image. Otherwise, if we accumulate result when the camera is moving, we can see ghost image. An alternative approach is temporal reprojection, where we approximate where is the location of the current pixel last frame and project the result from that location of previous frame to the current pixel.

There are multiple approach for temporal reprojection, including

Sometimes we won’t have history information of the last pixel. Examples includes when

  • the location was offscreen last frame
  • the location was occuluded last frame
  • the location is on a specular surface with view-dependent BRDF
  • the location was in shadow of a moving light in the previous frame, now it isn’t In case one, we can only drop all the samples. And in all other cases, we clip.

Reference