Lanczos Interpolation

This method is based on the 3-lobed Lanczos window function as the interpolation function.

The interpolation algorithm uses source image intensities at 36 pixels in the neighborhood of the point (x_S, y_S) in the source image:

x_S0 = int(x_S) - 2; x_S1 = x_S0 + 1; x_S2 = x_S0 + 2; x_S3 = x_S0 + 3; x_S3 = x_S0 + 4; x_S3 = x_S0 + 5;

y_S0 = int(y_S) - 2; y_S1 = y_S0 + 1; y_S2 = y_S0 + 2; y_S3 = y_S0 + 3; y_S2 = y_S0 + 4; y_S2 = y_S0 + 5;

First, the intensity values are interpolated along the x-axis to produce six intermediate results I₀, I₁, ... I₅:

Then the intensity D( x_D, y_D) is computed by interpolating the intermediate values I_k along the y-axis:

Here a_i and b_k are the coefficients defined as

a_i = L(x_S- x_Si), b_k = L(y_S- y_Si),

where L(x) is the Lanczos windowed sinc function:

To use this interpolation, set the parameter interpolation to IPPI_INTER_LANCZOS.