2-6 Interpolation of Image Data Figure 2.18 shows the process of geometric correction in which the original image data with distortions are transformed into geocoded image through resampling and interpolation.

There are three interpolation methods.

Nearest Neighbor
Resampled image data Q (x, y) is replaced by the nearest original image data Pkl.

Q (x, y) = k = IFIX (x + 0.5), l = IFIX ( y + 0.5)

Bi-linear
Resampled image data Q (u, v) is averaged by the four surrounding original image data as follows.

Q (u, v) = (1-u)(1-v) Pi,j+1 (1-u) VPij+1 + u (1-v) P i+i,j +uv P i+1, j+1

Where (u, v): normalized coordinates; 0 £ u £ 1, 0 £ v £ 1

Cubic Convolution
Cubic convolution is an image enhancement technique to stretch the contrast and sharpen the edges using the following spatial filter as shown in Figure 2.19 (c).

Resampled image data are computed using 4 x 4 = 16 surrounding original image data as shown in Figure 2.19 (d).