AIPS HELP file for MAXPIXEL in 31DEC24
As of Wed Nov 13 8:04:48 2024
HELP SECTION
MAXPIXEL
Type: Adverb (scalar)
Use: Specifies the maximum number of pixels to be searched
for Clean components during each major cycle of the Clark
version of Clean.
Null Value: 0 => 20050.
Tasks:
APCLN.......Deconvolves images with CLEAN algorithm
IMAGR.......Wide-field and/or wide-frequency Cleaning / imaging
SCIMG.......Full-featured imaging plus self-calibration loop with
editing
SCMAP.......Imaging plus self-calibration loop with editing
SDCLN.......Deconvolve images, switching to Steer-Dewdney-Ito
algorithm after a while.
Procedures:
LINIMAGE....Build image cube from multi-IF data set. MAXPIXEL is
passed to IMAGR.
"Verbs":
OBITIMAG....Access to OBIT task Imager without self-cal or peeling.
MAXPIXEL is used as in IMAGR,
OBITPEEL....Access to OBIT task Imager with self-cal and peeling.
MAXPIXEL is used as in IMAGR,
OBITSCAL....Access to OBIT task Imager with self-cal, NOT peeling.
MAXPIXEL is used as in IMAGR,
Discussion:
AIPS Clean algorithm was designed by Barry Clark and modified by Bill
Cotton. In it, a certain number of the highest pixels in the
residual image is loaded to the "AP" memory to be searched for
components during each major cycle. The performance and the results
of the clean depend a lot on how many pixels are searched. If too
few are searched, then each cycle will find only a few components and
there will have to be many (expensive) major cycles. If too many are
searched, then the algorithm wastes a lot of time searching and
subtracting from pixels it does not ever need. Also, when a large
number are searched, a larger beam patch is needed to avoid making
too much error inside the cycle. Use this option sparingly, but
values like 25000 or 30000 are found to speed cleans of large images
that develop many approximately equal pixels in the residual image.
EXPLAIN SECTION