The values for the focal length of the lens and the acquisition frame rate are very important since they have a determinant influence on the final look and feel of the movie. For instance, by increasing the focal length we can zoom-in on a desired image element, and by multiplying the frame rate we can record in slow-motion. Therefore it is best to choose these values before shooting, so as to accomodate the director’s vision. But it’s also common that in postproduction there appears the need to perform zoom-in on a shot (e.g. because there is an element at the frame boundary that we want to get rid of, like a microphone), or to turn it into slow-motion (typically for aesthetic reasons). Of course it’s out of the question to perform a re-shoot with the correct focal length and frame rate values, so we must carry out interpolation processes in space (for the zoom-in) or space and time (for slow-motion generation). Other reasons for zoom-in may be to increase the resolution of a movie (for exhibition in a higher resolution system) or a shot (to combine it with higher resolution shots). And a slow motion generation algorithm might be used for converting movies from one format to another with a different frame rate (altough this would be frame interpolation, not actual slow motion).