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SIGRANGE

SIGRANGE

Name


SIGRANGE()

Purpose


Selects the most significant data range in an image.

Explanation


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


OUTPUT = SIGRANGE( ARRAY )

Inputs


ARRAY = Array to take most significant range of.

Optional Inputs


None.

Outputs


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)
used

Notes


      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).

Restrictions


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
http://sohowww.nascom.nasa.gov/solarsoft/gen/idl/image/
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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