[daip] message from IMAGR

[Eric Greisen]

Michael Bietenholz writes:
 > My 31DEC01 multi-field IMAGR seems to be running much more slowly than
 > the 31DEC99 version.
 > 
 > I also keep geting messages like:
 > 
 > "TRY ANOTHER FIELD: this is  3.955E-03 < Second best  3.994E-03"
 > 
 > Can someone tell me what that message means?
 > 
This is a new behavior in the OVERLAP >= 2 mode.  It picks the next
field to image based on the max in the boxes BEFORE it is imaged with
the current residual data.  If, after that reimaging, its max is now
rather lower than another field, it will switch and try that other
field instead.  Otherwise, a noise field will be cleaned at some point
even though when correctly computed it has no pixels large enough for
loading in the AP.  Then all fields are recomputed.  It is an attempt
to find the best field to Clean next without too much re-imaging.  If
this does too much re-imaging, then the test should be refined.  In
the case above, for example, the 2nd best field (not yet re-imaged) is
only about 1% greater than the current guess (re-imaged).  To Clean
the current rather than revert to the 2nd would probably be fine in
this case.

Eric Greisen