The computer needed one thing from the artist. What?

Hunger (National Film Board of Canada) was drawn by Peter Foldès; its in-betweens were computed by Nestor Burtnyk and Marceli Wein of the National Research Council of Canada. Their system took the assistant's job: the artist drew the keys, and "the in-between frames are computed by interpolating between key frames". But a drawing is a pile of lines, and a wrong pairing ties it in a knot. The artist gave the pairing "by deciding on the order in which he traces the lines in the key image. The one-to-one correspondence between the source and the destination key is between stroke lines in the image." In 1991 the faces in Michael Jackson's Black or White ran on pairs of lines too (Beier and Neely, SIGGRAPH 92). Burtnyk and Wein, 1971: "An animator's ideas involve mainly pictures and their motion."

Our own drawings, in-betweened in straight lines as the 1971 system did; no frames from Hunger or Black or White.

Which two drawings would you morph?

Sources: N. Burtnyk and M. Wein, "Computer-Generated Key-Frame Animation", Journal of the SMPTE, 1971; "Computer Animation of Free Form Images", SIGGRAPH 75; National Film Board of Canada, Hunger; Festival de Cannes, 1974 awards; Academy Awards, 47th ceremony; Thaddeus Beier and Shawn Neely, "Feature-Based Image Metamorphosis", SIGGRAPH 92.
Sounds: our own, made in code (earshot, CC0).