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Selects the most significant data range in an image.


Selects out the most significant range in the data to be used in
displaying images. The histogram of ARRAY is used to select the most
significant range. Useful for scaling an image display.

Calling Sequence



ARRAY = Array to take most significant range of.

Optional Inputs



The function returns an array where values above and below the
selected range are set equal to the maximum and minimum of the
range respectively.

Optional Input Keywords

FRACTION = Fraction of data to consider most significant.
Defaults to 0.99
MISSING = Value used to flag missing points. Data points with this
value are not considered or changed.

Optional Output Keyword

RANGE = 2 element vector, giving the range (minimum and maxmimum)


      If the image array contains more than 10,000 points then SIGRANGE()
      uses random indexing of a subset of the points to determine the range
      (for speed). Thus identical calls to SIGRANGE() might not yield
      identical results (although they should be very close).


ARRAY must have more than two points. Fraction must be greater than 0
and less than 1.
SIGRANGE was originally part of the SERTS image display package.
Other routines from this package are available at
Note that this version of SIGRANGE does not include the non-standard
system variables used in the SERTS package.

Revision History

Version 1, William Thompson, GSFC, 12 May 1993.
Incorporated into CDS library.
Version 2, William Thompson, GSFC, 25 May 1993.
Changed call to HISTOGRAM to be compatible with OpenVMS/ALPHA
      Version 3, CDP, RAL, Add RANGE keyword. 16-Apr-96
Version 4, William Thompson, GSFC, 17 April 1996
Corrected some problems when range is too high.
Version 5, 13-Jan-1998, William Thompson, GSFC
Use random numbers to improve statistics when only using a
fraction of the array.
Version 6, 06-Mar-1998, William Thompson, GSFC
Change default to 0.99

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