Content-type: text/html Manpage of imsad


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imsad - Image search and destroy  




image analysis  


IMSAD fits a gaussian to the image histogram to determine the true image rms noise, then searches for islands of pixels above some cutoff, and attempts to fit gaussian components to the islands. The fitting is borrowed from the miriad imfit task and the island detection from the AIPS SAD task.

Pixels above the clip level are marked in yellow. Then a square region centred on each island is coloured in.

When fitting Gaussians, a cross is plotted at the midpoint of the island. Each island is displayed separately in the top left of the display as it is fit. The centroid of the fit is plotted.

Information about the fit for each island is given.  


The name of the input image data set.
The region of interest within the image (rectangular only).
Image intensity range to display. Default is min to max for the current plane being displayed.
Clip level. For input images of intensity, any pixels below the clip level are excluded from the fitting process. For other sorts of images (e.g. Stokes Q, U or V) pixels whose absolute values are below the clip level are excluded from the fit.

The clip level can be specified as a multiple of the true image rms (using the hist option) or as an absolute pixel value. No default.

The minimum extents for island boundaries. This would usually be some multiple of the beam extents in x and y (2,2 is the default). For images with no beam characteristics there is no default, the units in this case are pixels.
Sets the maximum number of boxes to return, if more then max are detected then the max boxes with largest peak flux / pixel are returned.
Will only report those islands detected within some angular radius of the specified coordinate pair. The default units are absolute pixels, eg. 16,18,10. If units other than the default are used you must specify these after the radius, eg. 10:34:45.3,-45:54:02, 0.005,hms,dms,degrees.
Extra processing options. Possible values are:

hist ....... compute the image pixel histogram and compute the

             true image rms
gauss ...... fit a gaussian model to each component fixed ...... the FWHM is fixed (circular cross-section) point ...... a gaussian with the characteristics of the
             point-spread-function is fit
box ........ return the island box extents arcsec ..... output box BLC/TRC units are arcsec offset from reference,
             default is absolute pixels
fiddle ..... interactively adjust the display lookup table (LUT),
             and alter the transfer function
nofit ...... do not perform any fitting noplt ...... disable the plotting features nodet ....... skip island detection and fit the box given by region
             - not implemented
PGPLOT plot device
Dataset to write fitted source parameters. Each line of this file summarises the result of the Gaussian fit for one island. Each line contains:

Island name, island number, ra and dec of island centroid, peak flux density, integrated flux density, deconvolved (from beam) major axis FWHM (arcsec), deconvolved minor axis (arcsec), deconvolved position angle (degrees), FLAG, DFLAG, FFLAG

FLAG: IFAIL value (an integer) means Gaussian fit did not converge

        F means failed to find covariance matrix for Gaussian fit
        N means it was not possible to attempt a Gaussian fit
        C converged OK

DFLAG: D deconvolution of size from beam OK

        P  deconvolution gave result close to point source
        ?  No synthesised beam so could not deconvolve
        F  deconvolution failed

FFLAG: F Integrated flux < peak flux (caused by beam > source size)

        If blank then ok.
If specified, output is written to the file given by log= instead of to the terminal.
Special purpose label




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Time: 18:35:38 GMT, July 05, 2011