% @(#)filterripp.hlq	19.1 (ESO-IPG) 02/25/03 14:28:41 
%++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
%.COPYRIGHT  (c)  1990 European Southern Observatory
%.IDENT      filterripp.hlq
%.AUTHOR     DB, IPG/ESO
%.KEYWORDS   MIDAS, help files, FILTER/RIPPLE
%.PURPOSE    On-line help file for the command: FILTER/RIPPLE
%.VERSION    1.0  25-NOV-1985 : Creation, DB
%----------------------------------------------------------------
\se
SECTION./RIPP
\es\co
FILTER/RIPPLE						25-NOV-1985 DB
\oc\su
FILTER/RIPPLE frame outframe  period [start,end]
	correct 1-dim. images for periodic ripple (Reticon)
\us\pu
Purpose:       correct one-dimensional images for periodic ripple
               (e.g. in Reticon data)
\up\sub
Subject:       Fourier transforms, periodic noise, microphonics.
\bus\sy
Syntax:        FILTER/RIPPLE frame outframe period [start,end]
\ys\pa
	       frame     = name of input frame
\ap\pa	
               outframe  = name of output frame
\ap\pa	
               period    = ripple period (in pixels)
\ap\pa	
               start,end = numbers of first and last pixel of range over
                           which analysis is to be performed

\ap\no
Note:          The program internally recognizes near-integer periods
               and accordingly uses two different algorithms.
	       For "odd" periods an internal rebinning is done (the result
               of which is not written on disk) to a step of 1/20 of the
	       period and then back to unity. Both rebinnings do not
               include an interpolation as this would require knowledge
	       of the nature and origin of the ripple.

	       "start" and "end" default to the first and last pixel of
               "frame". It is advisable to specify "start" and "end"
               so as not to include any spectral or instrumental
               features (remember that often the first and last few pixels
               of a spectrum contain rubbish!). The ripple correction will in
               any case be done on the entire frame.

	       The program works best if the slope of the spectrum (or
               the portion thereof which is analyzed) is small although
               an attempt is made to compensate its effect.
\on\exs
Examples:
\ex
               FILTER/RIPPLE OLD NEW 8 200,700
	       correct ripple in frame "OLD" with period 8,
               determine the amplitude over the pixels 200-700
\xe\ex	
               FILTER/RIPPLE CES RESULT 3.356
               correct frame "CES" for ripple with period 3.356,
	       the entire frame is used for the amplitude diagnostics
\xe\sxe
\res
Restrictions:\\   a) works in pixel space only with START = 1 and STEP = 1
\\
               b) if a significant portion of the pixels contain
                  negative fluxes, the program may abort

\ser
