Help for REPAIR

      REPAIR identifies bad lines (lines that are inconsistent with the
surrounding lines) and replaces them by interpolation of the nearest good 
lines. If the locations of the bad lines or line segments are known, the user 
may list the offending lines and use the ALL mode to repair just those lines.
If the locations of the bad lines are unknown, the program decides which lines
are bad by computing the interline correlation (and optionally the differences
in the means and the variances).
      REPAIR can now repair multichannel data in BSQ or BIL organizations. All
channels are tested in aggregate, and if the line is found to be bad, the line
is replaced in all channels. No specific channel repairs are presently 
implemented.
 OPERATION
      There are three modes of operation to REPAIR. The CORR and MV modes 
differ only in the tests employed to determine bad lines, but the ALL mode 
does no statistical testing, and is more closely related to the earlier VICAR 
program SAR. 
      In the ALL mode, lines or regions are specified by the user via the AREA,
LINESET, BADLINE, and/or MODULO parameters. These regions are replaced by means
of a linear interpolation, using the lines immediately above and below the 
region. Interpolation is performed in the line direction only, and the area 
outside the specified regions is unchanged.
      In the CORR and MV modes, the AREA, LINESET, BADLINE and MODULO 
parameters are used to identify regions to be examined for bad lines. If all 
three parameters are defaulted, the entire image is tested. Each line that is 
to be checked is tested by the following procedure:
      A. The line is compared to two reference lines: the last good line, and 
         the average of the next line and the last good line.
      B. If the correlation coefficients between the test line and both of the
         reference lines is less than the value of CORR, then the line is 
         considered bad. There is one exception to this test. If the ZOK (Zero
         OK) keyword is in effect, lines that are all zeroes are passed as
         good. The correlation coefficient is undefined for lines of constant 
         value, requiring this special case. A correlation coefficient of 0.0 
         is assigned to all other cases involving lines of constant DN.
      C. If the MV (Mean and Variance) mode is in effect, then two additional 
         tests are employed. The test line is considered bad if its mean is 
         different than the means of the reference lines by more than the value 
         of MEAN, or if its variance is different than both the reference line 
         variances by more than the value of VARIANCE.
 If a line is found to be bad, the entire line is replaced by a linear
 interpolation of the last good line and the next good line. 
      This algorithm is fairly sensitive to the values of the CORR, MEAN, and
 VARIANCE parameters. It may be necessary to run this program more than once
 in order to find an appropriate set of values. In general, the CORR and 
 VARIANCE values provide the best tests for random noise and hashed lines. The
 test of the means should only rarely be needed to reject a line.
      The coordinates used in the AREA parameter (SL,SS,NL,NS,...) refer to the
 input image, not the output image. This is important only if, in the size
 field, the starting line or starting sample is not one. 
      The user should also be aware that if two regions specified by AREA, 
 LINESET, or BADLINE contain the same line, the two regions will be combined 
 into one larger region that contains both original regions. This can cause
 problems, especially in the ALL mode, where more pixels may be modified than
 were intended.
      This program will run on byte, halfword, fullword, or real data. Up to
 100 regions may by given by each of the AREA, LINESET, and BADLINE parameters.
 If either MEAN or VARIANCE is not defaulted, the MV mode is automatically
 used.
 ORIGINAL PROGRAMMER:  John Addington
 
 CURRENT COGNIZANT PROGRAMMER: Ron Alley

 REVISION:  14 January, 2003  (MODULO option added)