The most difficult task for the special effects crew to achieve was to make live-action footage interact with separately filmed stop-motion animation – to make the interaction between the humans and the creatures of the island seem believable. The most simple of these effects were accomplished by exposing part of the frame, then running the same piece of the film through the camera again by exposing the other part of the frame with a different image. The most complex shots, where the live-action actors interacted with the stop-motion animation, were achieved via two different techniques, the Dunning process and the Williams process, in order to produce the effect of a travelling matte. The Dunning process, invented by cinematographer Carroll H. Dunning, employed the use of blue and yellow lights that were filtered and photographed into black-and-white film. Bi-packing of the camera was used for these types of effects. With it, the special effects crew could combine two strips of different film at the same time, creating the final composite shot in the camera. It was used in the climactic scene where one of the Curtiss Helldiver planes attacking Kong crashes from the top of the Empire State Building, and in the scene where natives are running through the foreground, while Kong is fighting other natives at the wall.