Help for REMRAY

PURPOSE:
Remray removes small artifacts such as cosmic ray or high energy charged 
particle tracks from images. The artifacts are always assumed to be brighter 
than the true image intensities.
Remray can remove small clusters of pixels which Remnoise cannot handle.

EXECUTION:
median inp=image out=median nlw=5 nsw=5
remray inp=(image,median) out=smooth tol=20

METHOD:
An input image has dn values of DN.
A model for the background is taken from the median image.
An activity measure is computed from the medians as the absolute value of
a derivative filter whose kernel is
-1 -1 -1
-1  8 -1
-1 -1 -1 
If DN-median exceeds GAIN1*(the median) + GAIN2*(the activity)
the pixel is reset to the median average over a 3 by 3 area..

The algorithm is as follows for each pixel:
1. Select a 3 by 3 window of DN(i,j).
2. Subtract the median window MED(i,j)
   HP(i,j)=DN(i,j)-MED(i,j)
3. Compute an activity measure A from:
the absolute value of a derivative filter whose kernel is
-1 -1 -1
-1  8 -1
-1 -1 -1 
6. If(HP(2,2) > GAIN1*MED(2,2) + GAIN2*A) then 
    DN(2,2)= the 3 by 3 median average.
   ( the (2,2) refers to the central pixel in the 3 by 3 window).

If the GAIN1 and GAIN2 factors are defaulted they are computed from TOL. To do
this remray computes histograms of the median intensity and the activity and
selects the upper few percent values. Then..
GAIN1=TOL/(max dn of medians)
GAIN2=TOL/(max activity of medians).


HISTORY:
3-1-99  J Lorre. 
COGNIZANT PROGRAMMER:  Jean Lorre