The first thing visitors will see at the entrance to the Museum of Modern Art’s sprawling Willem de Kooning retrospective, which opens on Sunday, is a wall of photographs that chronicle six stages in the creation of the legendary painting “Woman I” (1950-52). John Elderfield, MoMA’s chief curator emeritus of painting and sculpture, said he chose these images as a starting point because they illustrate “that de Kooning was an artist about process.”