How would you differentiatw collage from decollage​

Collage is a visual art form, where pieces of other images are grouped together to create a new piece of art. ... A decollage is created by removing part of the larger image to create something new. It is the opposite of collage were the image is built up by adding pieces.

Décollage, in art, is the opposite of collage; instead of an image being built up of all or parts of existing images, it is created by cutting, tearing away or otherwise removing, pieces of an original image.

c) from classical art