Flatten
From The Glossary of Digital Photography
(1) To make curled prints flat by carefully reverse rolling them. (2) The process of flattening an image by collapsing various layers to the single background image in an image-manipulation program such as Photoshop. The Photoshop command to collapse the layers is flatten image. All of the active changes made to the image in the layers are applied to the base image when the flatten command is used.
