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Last modified: December 2013

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AHELP for CIAO 4.9 Sherpa v1


Context: psfs


Send a PSF image to the imager (ds9).


image_psf( [id, newframe, tile] )


The image_psf command sends the 2D PSF data to the imager (ds9) for display. If a 1D PSF was loaded, use the plot_psf command ("ahelp plot_psf") instead. To view the filtered kernel which will be used in the convolution, use the image_kernel command.

  • id - the id of the data set to use; if not given, uses the default dataset id (id=1 by default, see "ahelp get_default_id")
  • newframe - add a new frame; default=False
  • tile - tile image frame; default=False

What is the difference between the PSF and the kernel?

The point spread function (PSF) is defined by the full (unfiltered) PSF image loaded into Sherpa or the PSF model expression evaluated over the full range of the dataset; both types of PSFs are established with the load_psf() command. The kernel is the subsection of the PSF image or model which is used to convolve the data. This subsection is created from the PSF when the size and center of the kernel are defined by the command set_psf(). While the kernel and PSF might be congruent, defining a smaller kernel helps speed the convolution process by restricting the number of points within the PSF that Sherpa must evaluate.


sherpa> image_psf()
sherpa> image_psf(2)
sherpa> image_psf(2, True)
sherpa> image_psf(2, newframe=True, tile=True)

The function sends image data from a PSF model to the imager, when that model has been defined by data read in from a PSF file. If no argument is given, the PSF model assigned to the default data set ID is assumed; the PSF data are sent to the current imager frame; and the imager frames are not tiled. If a different data set ID is given, then data from the PSF model for that data set are displayed. If the newframe option is set to True, the PSF data are displayed in a new imager frame. If the tile option is set to True, all imager frames are tiled for display.


See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.

See Also

contour_kernel, contour_psf, delete_psf, get_kernel, get_psf, image_kernel, load_conv, load_psf, plot_kernel, plot_psf, set_psf, show_kernel, show_psf

Last modified: December 2013
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