This filter makes several copies of the original image, in a same or reduced size, into a bigger (new) image.
Tile to New Size
Input boxes and their arrow-heads allow you to enter the dimensions for the new image.
The new image must be bigger than the original one. Else, you will get an image sample only. Choose sizes which are multiple of original sizes if you don't want to have truncated tiles.
Keep this option checked to avoid modifying your original image.