Using Sigma Clipping (1-D Fit Package)
This example shows the effect of using sigma clipping to reject data points from the fit using the 1-D Fit package. The pictures below compare fitting with and without sigma clipping enabled.
This figure shows a plot through an image having a flat background and a spike. We want to characterize the low-lying background data, but the tall peak will corrupt the fit. One way to exclude the spike from the fit is to use sigma clipping, which rejects the spike as "bad data".
This shows the same data as above, but with the 1-D Fit Toolbar opened and configured for a 5-term fit and no sigma clipping.
Below is the result of fitting 5 coefficients without enabling sigma clipping. The spike pulls the fit upward, causing extra ripples and making the fit useless for characterizing the data along the base.
For this fit, the 
was checked, then the 
was clicked to compute a new fit. The rejected
points were changed to the turquoise color. The fit is in
purple.
Highly magnified view of previous figure about the base of the peak. Notice how the fit tracks the point data near the base of the profile. The upper and lower sigma envelope is drawn in purple above and below the fit.
1-D Fit Package, 1-D Fit Toolbar, Sigma Clipping, Point Deletion