ISTAT-Provides some statistics about an image (max, min etc.)

Description:

ISTAT examines an image, or a rectangular subset of an image or spectrum, and outputs a number of statistics about it, such as maximum and minimum value, mean and sigma, etc. The results are used to set Figaro user variables, so can be used by Figaro procedures. There are a number of examples in the documentation

Parameters:

IMAGE

The name of the image (or spectrum) for which statistics are to be determined.

YSTART

First Y value to be used.

YEND

Last Y value to be used.

XSTART

First X value to be used.

XEND

Last X value to be used.

PASS2

setting PASS2 makes ISTAT take two passes through the data in order to calculate Sigma more accurately. This accuracy is, of course, gained at the expense of time taken. For cases where fewer than 10,000 pixels are involved, ISTAT always uses two passes, since the other overheads dominate the time taken. If in doubt, try both, and see if the slower algorithm gives significantly different answers to the faster one. If so, use PASS2.

MEDIAN

Setting MEDIAN makes ISTAT calculate the median value in the specified range. This can be a time-consuming operation, so is not performed by default.

See also:

KAPPA: HISTAT, HISTOGRAM, INSPECT, MSTATS, NUMB, STATS.

Source comments:

 I S T A T

 Examines an image (or a subset of an image) an determines
 a number of useful statistics about the data in it, such as
 the mean, max and minimum values.  For a full list, see below
 under 'user variables'.

 Command parameters -

 IMAGE  (Char) The name of the structure containing the image.
 YSTART (Numeric) The Y value for the start of the subset.
 YEND   (Numeric) The Y value for the end of the subset.
 XSTART (Numeric) The X value for the start of the subset.
 XEND   (Numeric) The X value for the end of the subset.

 Command keywords

 PASS2   If set, the sigma value is calculated using two
         passes throught the data.  The one-pass algorithm normally
         used is prone to rounding error when large numbers of
         pixels are involved, but is rather faster.  If fewer than
         10,000 pixels are involved, ISTAT always uses two passes,
         since the other overheads dominate the time taken.
 MEDIAN  If set, the median value of the image data is
         calculated (a possibly time-consuming business).

 User variables -   ("<" output)

 (<) STAT_TOTAL   The sum of the data.
 (<) STAT_MIN     The minimum data value.
 (<) STAT_MAX     The maximum data value.
 (<) STAT_MEAN    The mean data value.
 (<) STAT_MEDIAN  The median data value (only set if MEDIAN set)
 (<) STAT_XMAX    The x-value of the pixel where the max was found.
 (<) STAT_YMAX    The y-  "   "   "    "     "     "   "   "    "
 (<) STAT_XMIN    The x-  "   "   "    "     "     " min   "    "
 (<) STAT_YMIN    The y-  "   "   "    "     "     "   "   "    "
 (<) STAT_SIGMA   The standard distribution of the data
 (<) STAT_SIZE    The number of pixels examined
 (<) STAT_XSTART  The first pixel number examined in X
 (<) STAT_XEND    The last    "     "        "     " X
 (<) STAT_YSTART  The first pixel number examined in Y
 (<) STAT_YEND    The last    "     "        "     " Y

                                  KS / CIT 7th June 1984