Help for STRETVAR

PURPOSE:

stretvar perform a linear stretch such that the low and high stretch
limits vary as a function of line number.  The stretch limits are
specified by the user for a number of discrete lines via the TABLE
parameter.  The stretch limits for each line between those specified
are computed by interpolation.

This program is useful in cases where the picture contrast varies
systematically for the top to the bottom of the image.

EXECUTION:

	stretvar IN OUT              TABLE=(LINE1,ILOW1,OLOW1,IHIGH1,OHIGH1,                    LINE2,ILOW2,OLOW2,IHIGH2,OHIGH2,                                   . . .
                                  . . .
		   LINEn,ILOWn,OLOWn,IHIGHn,OHIGHn)

 All values in the TABLE parameter are integers.  The values are
 entered in sets of five, where LINEj specifies the line number and
 ILOWj, OLOWj, IHIGHj, OHIGHj specify the low and high stretch limits
 for the input and output images such that:

		ILOWj maps to OLOWj
            and IHIGHj maps to OHIGHj

 The lines must be specified in ascending order.  LINE1 must be the
 first line of the image (i.e. LINE1=1) and LINEn must be the last line
 of the image.  The stretch limits may be explicitly specified for a
 maximum of 50 lines.  Note that TAE also restricts command line
 length to 2048 characters.

 Note that although stretvar will accept a size field specification,
 SL and SS are ignored.

OPERATION:

 For the specified lines L1,L2,...,Ln, stretvar performs a linear stretch
 as specified by the low and high stretch limits for the input and output
 images.  Let IDN and ODN represent the input and output DN values for
 a given pixel.  Then
			     (OHIGH - OLOW)
		ODN = OLOW + -------------- X (IDN - ILOW)
			     (IHIGH - ILOW)

 For every line L between Lj and Lj+1 the low and high stretch limits
 are computed by linear interpolation:

			       ILOWj+1 - ILOWj
		ILOW = ILOWj + --------------- X (L - Lj)
				  Lj+1 - Lj
 
EXAMPLE:

	stretvar INP=A OUT=B TABLE=(1,0,0,255,255,  			          100,127,0,128,255)
 
 	The input image A is assumed to contain 100 lines.  The applied
        stretch will gradually increase in severity, with no contrast
        change for the first line of the image, and separation into two
	grey levels for the last line.

 WRITTEN BY:  B. Gokhman, 10 March 1983
 COGNIZANT PROGRAMMER:  G.M. Yagi

 PROGRAM HISTORY:
  29 MAR    1994...CRI...MSTP S/W CONVERSION (VICAR PORTING)
  28 AUG    1986...G.M.Yagi...............Fix bug in call to MVE
  26 AUG    1986...G.W.Garneau............Convert to VICAR2
   6 SEP    1983...A.S.M..................VICAR1 conversion

PARAMETERS: