17.15 STATISTIC

[DISPLAY\]STATISTIC [DataCube [FirstPlane [LastPlane]] [/EDGE Margin] [/NOISE VarNoise [ONLY]]

Compute some basic statistics (min, max, mean, rms,...) on the specified DataCube buffer (default: CLEAN) and planes (default: variables FIRST and LAST). The current polygon or mask (see commands SUPPORT and MASK) is used to define the area on which the pixels are to be taken into account, except when /EDGE 0 is mentionned.

In addition to Min and Max, the command prints 3 noise numbers:

 - the rms inside the current support (whose value depends on the source
 strength and structure)
 - the rms outside of the support (a good estimate of the effective
 noise), returned in variable STAT_NOISE.
 - the theoretical thermal noise (that would be the expected noise unless
 the data is dynamic range limited, or unless the weights were
 not set properly)

For primary-beam corrected images (SKY), the noise is non uniform. In this case, the rms outside the support is actually derived through a Gaussian fit to the intensity histogram, whose shape is non-Gaussian as larger noise happens at mosaic edges. This is a better approximation on the rms noise towards the mosaic center.