Program:       DECIM

Purpose:       Decrease size of a set in any direction with an
               integer factor

Category:      MANIPULATION, CALCULATION

File:          decim.c

Author:        M. Vogelaar

Keywords:

   INSET=      Give set (, subsets) to decimate:

               Maximum number of subsets is 2048.


   BOX=        Frame for input subsets.                 [entire subset]


   DECIM=      Give decimation:				        [1,...]

               The user can specify a decimation factor for each axis
               in a subset. The default value for each axis is 1.
               Negative values are not allowed.


** SHIFT=      Shift in start of decimation:                        [0]

               Specify which of the 'decim'  number of pixels
               will be transferred to the new created output pixel.
               If for example a decimation factor 3 is specified, the
               pixels 0, 1, 2 create a new output pixel containing the
               value of the original pixel 0 by default. However, if
               the user wants to transfer one of the other pixels,
               he has to specify a shift. For the decimation factor 3
               the shifts 1 and 2 are allowed. Of negative shifts, the
               absolute values are taken and of shift values greater
               than (decimation - 1) the modulus is calculated.


   OUTSET=     Give output set (, subsets):

               Output set and subset(s) for the result. The number of
               output subsets is the same as the number of input sub-
               sets.


Description:   Decimate data in each specified direction of a subset.
               The decimation factor must be an integer number.
               In the output, pixel 0 will always be retained.
               If for example the user specified the decimation factor
               3, then the pixels -9, -6, -3, 0, 3, 6, 9 etc. will be
               in the output. If he also specified for this axis a
               shift of 1, the pixels  -5, -2, 1, 4, 7 etc. will be
               transferred. A possible use of the shift could be the
               creation of sets made with different shifts to combine
               them to a new set with flux that can be compared to
               the flux of the original (not decimated) set.


Example:

Updates:       ... ..,  1990: VOG, Document created.
               jun 11,  1996: VOG, Bug in output size removed.
               Oct  1,  1996: VOG, DECIM could not handle subsets:
                                   out=0 initialisation was move from
                                   outside to inside subset loop.