Help for HSTRETCH

PURPOSE

     "hstretch"  is a VICAR applications program used for  the 
     production  of binary masks and for modifying  specific 
     DN  values  of  images.   Operation of the  program  is 
     similar to the table stretch option of STRETCH, however 
     the parameter structure is often simplified.  The major 
     feature of "hstretch" is that only those DN values  which 
     are to be modified need to be listed as parameters.
TAE COMMAND LINE FORMAT

     hstretch INP=A OUT=B SIZE PARAMS

     where


     INP                 is an input file.

     OUT                 is an output file.

     SIZE                is a standard VICAR size field.

     PARAMS              is a standard VICAR parameter field.
OPERATION          

     A  stretch  table  is  set  up  based  upon  parameters 
     specified  via  the QTABLE or TABLE  keyword.   All  DN 
     values  not  specified either remain  unchanged  (TABLE 
     option)  or are stretched to the background DN  (QTABLE 
     option).

EXAMPLES

     hstretch INP=A OUT=B HALF VALUE=100 BVALUE=0
              QTABLE=(32      1      2067,                       96      4        39)

     In this example, a halfword dataset is input to yield a 
     halfword format binary mask.   The primary value of the 
     mask  will be 100 DN while the background value will be 
     0   DN.    Only   the  values   listed   after   QTABLE 
     (32,1,2067,96,4,39)  will be stretched to 100 DN.   All 
     other DN values of the input image will be stretched to 
     0 DN.

     hstretch INP=A INP=B
          TABLE=(24   1    38    0    117    1     25     3    
                 36   2    50    3     51    4     52     5)

     In this example both input and output datasets are byte 
     format  and the table transfer mode has been specified.  
     Only the following values will be stretched,  all other 
     will remain unchanged.

            OLD DN          NEW DN

               24              1
               38              0
              117              1
                .              .
                .              .
                .              .
               51              4
               52              5

     When using the table mode all values to be changed must 
     be specified.  Consequently,  if the primary purpose of 
     the  stretch is to enhannce the contrast of  an  image, 
     VICAR  program "stretch" will be easier to use,  as  only 
     the "posts" of the stretch must be specified.  However, 
     when  the  purpose  of  the stretch is  to  compress  a 
     dataset such as a land cover classification, or if only 
     a  few DN values are to be changed while others are  to 
     be unchanged, "hstretch" may be more useful.

RESTRICTIONS:
     Both the QTABLE and TABLE parameters 
     may  not appear in  the  same  parameter 
     dataset.

WRITTEN BY:            A. L. Zobrist            1 May 1978
COGNIZANT PROGRAMMER:  N. D. Ritter
REVISION:              4                       22 Jun 1994

REVISION SUMMARY:
     Made portable for UNIX  AMS (CRI)  5 Sep 1994
     Added Test Proc         NDR       22 Jun 1994