SMOOTH
Smooths an input map using various methods, all based upon a con-
volving kernel of 5 points large only. This method is crude, but
very fast, and supports blanking in principle... Data cubes are
processed plane by plane.
1. BOX A simple 5 by 5 boxcar smoothing. This is a very strong
smoothing...
2. GAUSS A gaussian smoothing. The gaussian is sampled on a 5 by 5
grid so it must not be too broad. 3 pixels seem a maximum. Use
task GAUSS_SMOOTH if you want to smooth with a broader gaus-
sian, but beware it does not handle properly blanked pixels.
3. HANNING Smoothing by a 5 by 5 pyramid, with weights 3 2 1.
4. USER User defined smoothing coefficients on a 5 by 5 grid,
assuming biaxial symmetry. Hence 6 coefficients only are re-
quired, S00 S10 S11 S20 S21 S22. The corresponding smoothing kernel
is :
S22 S21 S20 S21 S22
S21 S11 S10 S11 S21
S20 S10 S00 S10 S20
S21 S11 S10 S11 S21
S22 S21 S20 S21 S22
Such a generalised "smoothing" enables some image enhancement
based on gradients (e.g. with weights 4 -1 0 0 0 0). The
"smoothed" image is normalised by the sum of absolute values of the
coefficients.