AIPS HELP file for CONVL in 31DEC22
As of Tue May 30 11:13:12 2023
CONVL: Task to convolve two images.
INNAME Image name (name)
INCLASS Image name (class)
INSEQ 0.0 9999.0 Image name (seq. #)
INDISK 0.0 9.0 Image disk drive #
OPCODE Operation desired:
GAUS, GMOD, IMAG, IMAC,
BLC Bottom left corner
TRC Top right corner
Convolving image (IMAG, DGAU)
IN2NAME Image name (name)
IN2CLASS Image name (class)
IN2SEQ 0.0 9999.0 Image name (seq. #)
IN2DISK 0.0 9.0 Image disk drive #
OUTNAME Image name (name)
OUTCLASS Image name (class)
OUTSEQ -1.0 9999.0 Image name (seq. #)
OUTDISK 0.0 9.0 Image disk drive #
IMSIZE Size of box to find position
of max in output image (IMAC)
BMAJ -999.9 FWHM(asec) maj. axis output.
beam - required except IMAG
BMIN -999.9 FWHM(asec) min. axis output
BPA -360.0 360.0 position angle
FACTOR Unit conversion factor;
clip inv Gaussian level DCON
DOBLANK -1.0 1.0 >= 0 => reblank output images
where input was blanked
BADDISK Disks to avoid for scratch.
Use: CONVL convolves your map with a either an eliptical gaussian or a
specified convolving image. Strictly, only the inner quarter of
the map is properly convolved, but for the Gaussian this problem
may not be apparent. CONVL uses a 2D FFT, and so it cannot
properly handle images containing blanks. It will (in 31DEC04)
replace blanks with 0.0, do the convolution, and then put the
blanks back. Nonetheless, the effect of the 0.0 will be felt in
non-blank pixels. The second image must not contain blanked
pixels. CONVL surrounds images with sizes other than a power of
2 with zeroes up to the next power of 2, convolves using the 2D
FFT, and then removes the borders for output.
INNAME......The input image name. Standard defaults.
INCLASS.....The input image class. Standard defaults.
INSEQ.......The input image seq. #. 0 => highest.
INDISK......The input image disk drive #. 0 => any.
OPCODE......A code indicating the desired operation.
'GAUS' => convolve the image to the specified Gaussian.
'GMOD' => convolve the image with the specified Gaussian
'IMAG' => convolve image 1 with the second image.
'IMAC' => crosscorelate image 1 with the second image.
'DCON' => deconvolve the image from specified Gaussian.
'DGAU' => convolve the image with the deconvolution of
the Gaussian and the second image (Gaussian
divided by image in Fourier space)
blank => 'GAUS'
BLC.........The bottom left corner of a subimage to be convolved.
(0's => 1,1,1,1,1,1,1)
TRC.........The top right corner of the subimage to be convolved.
(0's => all of image from BLC)
IN2NAME.....The convolving image name. Standard defaults. Must be
same size and cell spacing as INNAME.
IN2CLASS....The convolving image class. Standard defaults.
IN2SEQ......The convolving image seq . #. 0 => highest.
IN2DISK.....The convolving image disk drive #. 0 => any
OUTNAME.....The output image name. Standard defaults.
OUTCLASS....The output image class. Standard defaults.
OUTSEQ......The output image seq. #. 0 => highest unique.
Input file (only) may be overwritten.
OUTDISK.....The clean disk drive no. 0 => highest with space
IMSIZE......Size of the box used to calculate max position in the
output image. Used only if OPCODE='IMAC'
Must be odd!!! 0 => 5, 5
BMAJ........Required for all OPCODEs except IMAG: the FWHM (asec)
major axis of the desired output beam. 0 -> Clean beam
for DCON only, for GAUS task finds smallest beam that
will work, for rest it is an error. Other than
IMAG, it will be deconvolved from the clean beam if the
input image is a clean image. If the deconvolution
fails, the program will terminate.
NOTE: as of 29 June 2010, the task will read a CG table
if present and determine the Clean beam for each channel
from it. The Gaussian used will then vary from channel
to channel and will be fully reported in the messages
and the history file.
BMIN........The FWHM (asec) minor axis of the output beam.
If <= 0 BMIN = BMAJ
BPA.........The position angle in the unrotated image of BMAJ.
FACTOR......All OPCODEs except DCON: the conversion factor for the
image units. This value of FACTOR if specified should
be the ratio of the new beam area to the old beam area.
If FACTOR is > 0.0, it will be used to convert from
JY/(old beam) to JY/(new beam). If FACTOR is 0.0 or
less, it will be determined from the output beam size
and any CLEAN beam stored in the catalog. If FACTOR is
not given and cannot be computed it is set to 1.0 and
the map units are changed to "UNDEFINE". If flux per
pixel output is desired then use FACTOR=1.0.
If the input image is not measured in JY/BEAM,
OPCODE=GAUS, and FACTOR <= 0, then
FACTOR = NPIXINBEAM
= ALFA * BMAJ * BMIN / (Xspace*Yspace)
where NPIXINBEAM is the number of pixels in the
convolving beam and
ALFA = PI / (4 * ln(2)) = 1.13309
DCON only: FACTOR is instead the limit in the value of
1/Gaussian. <= 1.01 => 1000.
DOBLANK.....>= 0 => reblank those pixels that were blanked in the
input image. This still leaves pixels around the
blanked affected by the use of 0.0 in the convolution.
NOTE the nonstandard usage where = 0 is TRUE.
< 0 => leave previously blanked pixels at whatever the
convolution produced from the 0.0 used instead of the
BADDISK.....This array contains the numbers of disks on which it is
desired that scratch files not be located. BADDISK has no
effect on input and output maps.
A remark about convolving a map which has been CLEANed
(added by DCW, 15 October 84)
In the help text above under the heading for BMAJ it says:
"[BMAJ] will be deconvolved from the clean beam if the image is
a clean image." What this really means is that CONVL will
attempt to produce a map which has the desired clean beam
shape, and in the process it will account for an existing beam
as declared in the header. This is done by deriving the
parameters of a Gaussian which when convolved with the existing
clean beam will produce the desired beam (the parameters of
this beam are listed in the history file). Obviously this
scheme only works when the desired beam is larger than the
existing beam (use the DGAU option if you want to deconvolve).
Please note that AIPS has tools for inserting clean beam
parameters into headers if they are not already there.
OPCODE 'GMOD' ignores the Clean beam information and simply convolves
with the specified Gaussian having parameters BMAJ, BMIN, and BPA.
A preliminary explanation of the 'DGAU' option
(added by DCW, 26Sept84)
Suppose that the second image contains the beam pattern of the
first image. Then DGAU will convert the effective beam of the
input image to the specified Gaussian. If the specified
Gaussian is narrower than the original beam this amounts to a
simple linear deconvolution scheme. The operation is done by
dividing the transform of the specified Gaussian by the
transform of the second image, and multiplying the quotient by
the input image. The quotient is set to zero when the transform
of the second image is zero.
An important application of DGAU is "cleaning up" the seeing
profile of an optical image. This is done by specifying a
circular Gaussian which is a good fit to the observed profile
(i.e., the second image). DGAU will then correct for the
ellipticity of the profile and its excess intensity in the
wings, producing an image which has a nice Gaussian beam,
although no resolution enhancement.