Linear Interpolation:

X1: X: X2:
Y1: Y: Y2:

Bi-Linear Interpolation:

X1: X: X2:
Y1: F(X1,Y1): F(X,Y1): F(X2,Y1):
Y: F(X1,Y): F(X,Y): F(X2,Y):
Y2: F(X1,Y2): F(X,Y2): F(X2,Y2):