Bicubic interpolation
From The Glossary of Digital Photography
A method of averaging adjacent pixels to create new pixels in between. Bicubic interpolation uses the values of surrounding pixels in its calculations in a weighted average where the closest pixels are given more weight than those farther away. This is one of the most popular methods of producing additional pixels when an image is enlarged in size. Compared to other interpolation methods, this bicubic takes longer to compute, but is generally a better representation of the original. There are now several versions of bicubic interpolation available in Photoshop: bicubic smoother, which is designed to make more-pleasing enlargements of images; bicubic sharper, which is designed to make more-pleasing reductions of images; and the original bicubic interpolation.
