Bilinear interpolation - Wikipedia
https://en.wikipedia.org/wiki/Bilinear_interpolationIn mathematics, bilinear interpolation is a method for interpolating functions of two variables (e.g., x and y) using repeated linear interpolation.It is usually applied to functions sampled on a 2D rectilinear grid, though it can be generalized to functions defined on the vertices of (a mesh of) arbitrary convex quadrilaterals.. Bilinear interpolation is performed using linear interpolation ...