Force large images sizes

Hello,

For a specific need in a plugin on which I work, i need to force image size even for lower resolution images.
For exemple, my biggest size is 1040 x 1220 px, and I want the image smaller than that to be enlarged. By default wordpress is not enlarging image, but I remember a plugin doing this (don’t remember the name).
As I don’t wan’t to use a plugin, is there a way to do this with the API ?

Hopping I was clear enough, thank you for the help ??