Nearest neighbor
From The Glossary of Digital Photography
A method of interpolation of data that is also known as piecewise constant interpolation. In digital image processing, when a digital image is enlarged, one way that the new values are calculated is by interpolating each new point based on an average of the values of the nearest neighbors. Another way is simply to use the value of the nearest neighbor. Both of these are quick and easy ways to interpolate the image file, but there are better methods available such as linear interpolation, polynomial interpolation, or bicubic interpolation. See also interpolation
