The term repoussé describes a metalworking technique in which object faces are shaped and patterned by hammering on the opposite side. In Photoshop, the Repoussé command converts 2D objects into 3D meshes, which you can precisely extrude, inflate, and reposition in 3D space.
The Repoussé command works with RGB images. If you start with a grayscale image, Repoussé converts it to RGB. The Repoussé command is not available for CMYK or Lab images.