In the Resize dialog (Image | Resize) there are several methods available for enlarging a picture
Examples of doubling the size of a picture is shown below. Bilinear interpolation in general performs well
and is very fast, but for increasing the size to 150% or above the Wiener filter or bicubic spline gives
the best results. Wiener filtering is especially superior for exactly 200%, 400%, or enlarging by any power of two.
The sinc method is included because of the close relations to the sampling theorem.
The difference between the results is easiest to see at the edges of the thin bright branches.
Cardinal sine (sinc)
Wiener filter, M=4
Wiener filter, M=6
XBR (under Pixel art resize)
Waifu2x (under Pixel art resize)