rms
and flux
parameters - these parameters
should be set with some care, or some experimentation may be necessary.
Various parameters to the task maxen are described below:
default
image are not too important, though it should be positive valued if the
Gull and Skilling entropy measure is used.
model
is some initial estimate of the deconvolved
image (units of Jy/pixel). In principle,
the model
image is simply a way to kick start maxen
towards the
correct solution. In principle it should not affect convergence to the final
solution or its quality - it should just speed up the process. In practice,
a good initial model
can sometimes help.
niters
gives the maximum number of
iterations that maxen
will attempt before giving up if it does
not converge. For low dynamic-range images, 10 iterations are usually
sufficient. Higher dynamic-ranges (greater than 1000) can require 30
iterations to converge. The default maximum number of iterations is 20.
rms
is too
large, the output image will be too smooth. If it is too small,
convergence will be prevented. A useful trick is to underestimate
rms
and then stop after a few iterations, and then reset
rms
to the level achieved up to that point. Do not leave
rms
unset.
flux
specifies how the zero-spacing flux density
is to be estimated. There are three modes of use. First, you specify a
known value which must be fitted to within 5%. Second, if you have no
idea what the zero-spacing flux density is, then leave flux unset;
maxen
will attempt to estimate it. Third, if you have a rough
idea (within a factor of 2, say) then set flux
to the negative of
your guess. If at all possible, you should give some estimate of the
total flux density.
MAXEN | |
map=vela.imap | Dirty image |
beam=vela.ibem | Dirty beam |
model | An initial solution solution - generally unset |
default | The image that the solution should tend |
towards - generally unset | |
out=vela.ivm | Output dataset |
niters=20 | Maximum number of iterations |
region= | Region to be deconvolved |
measure | Leaving unset gives you the Gull measure |
flux= | Total source flux - give some value |
rms= | Rms noise in the dirty image - IMPORTANT! |
q= | AN estimate of the value of the beams main lobe. |
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