This tool finds all 2-dimensional (RA/dec) regions in the given 4D (only!) image which are contiguous sets of pixels (islands) above the given ] threshold.  It creates a box for each island, a rectangular "cutout". The boxes are stored as regions in the output regionfile.  Works on multi-plane images, but only boxes 2-D regions in each plane. (Doesn't create cubes/3D boxes.)
NOTE: THIS TASK WILL NOT WORK ON IMAGES THAT DO NOT HAVE 4 DIMENSIONS WHICH INCLUDE A DIRECTION COORDINATE, A SPECTRAL COORDINATE, AND A STOKES COORDINATE. If your image has, eg just a direction coordinate, you can add the required axes using ia.adddegaxes()and remove them post-run with imsubimage with dropdeg=T.
       imagename -- Name of input images:
               default: none; example: imagename='myimage.image'
       regionfile -- Name of output region file (adds extension .rgn).
               default: none; if not given uses imagename+'.rgn'
       threshold -- value (with units) to use for island threshold.
               default: 0.0.
       maskname -- Optional output mask name.
               default: '' (do not write mask image)
       chanrange -- Range of channel ids
               default: '' (find boxes for all channels)
               example: '5~7' (find boxes for channel 5,6,7
       polrange -- Range of polarization ids
               default: '' (find boxes for all polarizations)
               example: '0~1' (find boxes for polarization 0,1
       minsize -- minimum size of island to get a box (in number of pixels)
               default: 2
       diag -- count diagonal connections as same island or not
               default: False
       boxstretch -- number of pixels to increase outward size of each box; can
               range from -1 to 5.
               default: 1
       overwrite -- Overwrite existing region file and/or mask?
               default: False.  If False, gives warning if file exists.