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image.twopointcorrelation  Function
1.1.1 Compute two point correlation function from the image
Description
This function computes twopoint autocorrelation functions from an image.
By default, the autocorrelation function is computed for the Sky axes. If there is no sky in the image, then the first two axes are used. Otherwise you can specify which axes the autocorrelation function lags are computed over with the axes argument (must be of length 2).
Presently, only the Structure Function is implemented. This is defined as :
where lx,ly are integer lags in the x (0axis) and y (1axis) directions. The ensemble average is over all the values at the same lag pair. This process is extremely compute intensive and so you may have to be patient.
In an autocorrelation function image there are some symmetries. The first and third quadrants are symmetric, and the second and fourth are symmetric. So in principle, all the information is in the top or bottom half of the image. We just write it all out to look nice. The long lags don’t have a lot of contributing values of course.
Arguments
Inputs 
 
outfile 
 Output image file name. Default is unset.
 
 allowed:  string 

 Default: 
 
region 
 Region selection. See ”help par.region” for details.
Default is to use the full image.
 
 allowed:  any 

 Default:  variant


mask 
 Mask to use. See help par.mask. Default is none.
 
 allowed:  any 

 Default:  variant


axes 
 The pixel axes to compute structure function over. The
default is sky or first two axes.
 
 allowed:  intArray 

 Default:  1 

method 
 The method of computation. String from
’structurefunction’.
 
 allowed:  string 

 Default:  structurefunction 

overwrite 
 Overwrite (unprompted) preexisting output file?
 
 allowed:  bool 

 Default:  false 

stretch 
 Stretch the mask if necessary and possible? See help
par.stretch. Default False
 
 allowed:  bool 

 Default:  false 

bool
Example
"""
#
print "\t\t twopointcorrelation Ex 1 \t"
ia.maketestimage(); # Output image is virtual
ia.twopointcorrelation() # Output image is virtual
#
"""
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