CImCombine:MtmSigmaClip

The MtmSigmaClip method merges the pixel values using iterative sigma-clipping to remove high and lower value outliers more than some number of sigmas from the median at each location.

Syntax

CImage = CImCombine:MtmSigmaClip( CImageSet )

CImage = CImCombine:MtmSigmaClip( CImageSet, nHigh )

CImage = CImCombine:MtmSigmaClip( CImageSet, nHigh, nLow )

CImage = CImCombine:MtmSigmaClip( CImageSet, nHigh, nLow, nIter )

where

CImageSet contains the collection of images to be combined.

nHigh is the number of sigmas above the median for rejecting points; default value is 2.5.

nLow is the number of sigmas below the median for rejecting points; default value is 2.5.

nIter is the maximum number of rejection iterations to perform; default value is 5.

CImage is a new image created by this method. On failure, nil is returned.

Each pixel in the output image is the median value of all images except those rejected by the sigma clipping criteria. The value of sigma is computed independently at each location. In order for the MtmSigmaClip method to work properly, normalization must be done as part of the combining.

Example

Suppose a CImageSet named S exists. The following script combines the images by the MtmSigmaClip method by excluding points more then 2.5 sigmas above the median and 5 sigmas below the median. The images are normalized by the Median statistic computed inside the central 10% of the image:

C = CImCombine:new()	-- create a CImCombine object
R = NewRect(10,50,10,50)	-- central 10% of the image
C:SetRelRect( R )	-- specify CImage and CRect to measure
C:SetNormStat("median")	-- use the SigmaClip as the normalization statistic
C:SetNormMethod("scale")	-- scale to normalize the image set
I = C:MtmSigmaClip(S,2.5,5,5)	-- combine image set and return new image
I:Display()	-- show the new image