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% @(#)rebin_deco.hlq 19.1 (ESO-IPG) 02/25/03 13:30:33
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REBIN/DECONVOLVE 04-OCT-1988 LL,DB
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REBIN/DECONVOLVE frame psf result zoom_x,zoom_y n_iter
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rebin image linearly in space and simultaneously deconvolve it with psf
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Purpose: Rebin an image linearly in space and simultaneously deconvolve
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it with user-supplied point spread function.
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(Reference: L.B. Lucy: 1974, Astron. J. 79, 745-754)
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Syntax: REBIN/DECONVOLVE frame [psf] result zoom_x,zoom_y [n_iter]
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frame = name of input image
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psf = name of point spread function image (default: psf)
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result = name of result frame
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zoom_x,zoom_y = zoom factors in X and Y
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no_iter = number of iterations, defaulted to 1
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Note: 1.) It is highly recommendable first to remove the
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background to the lowest possible level, however NOT
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thereby introducing pixels with negative fluxes. See also
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commands FIT/FLAT_SKY, SUBTRACT/SKY, and FILTER/FILL.
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2.) The PSF must have odd numbers of pixels in both X and Y
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(which however do not have to be same for both coordinates);
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it must be centered on the central pixel. The step sizes
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must be the ones desired for the result frame. If the
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empirically determined PSF (not zoomed) is n pixels wide,
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it is recommended to construct from it the required
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zoomed (by a factor z) PSF to have (n+2)*z pixels.
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3.) The zoom factors must be odd integers and consistent with
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the ratios of the step sizes of inframe and psf. Zoom
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factors less than unity are illegal. For zoom_x =
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zoom_y = 1, the command is functionally equivalent to
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DECONVOLVE/IMAGE (but slower!).
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4.) The result frame must have the same step size as the
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point spread function. The number of pixels must be
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compatible with the number of pixels of the input frame
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5.) If MID_WORK contains a file 'result.bdf', this file
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will be interpreted as an initial approximation of the
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result. Using the command n times with n_iter=1
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therefore has the same effect as using it once with
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n_iter=n except that intermediate results can be inspected.
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6.) The command can be used particularly profitably in order
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to improve the appearance of images with sparsely sampled
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PSF's where the smearing effects of conventional rebinning
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unwanted. It may also help to bring out faint features
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more strongly against the background. Depending on various
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factors, a larger number of iterations does not necessarily
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7.) The contents of each pixel is interpreted as flux density
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(e.g. surface brightness), i.e. flux per unit area in world
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coordinates. This means that the sum over all output pixels
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equals the sum over all input pixels times zoom_x times
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8.) Edge effects are suppressed by extrapolating the frame
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beyond its edges at a constant level and with the flux of
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the last pixel observed.
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9.) Large frames in combination with large zoom factors may
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exceed the available virtual memory.
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REBIN/DECO observed seeing true 3,5 2
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Expand image observed.bdf by factors 3 and 5 in X and Y,
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respectively. At the same time deconvolve with psf seeing.bdf
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using 2 iterations. The result will be stored in frame
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true.bdf which will be newly created if not already existing.
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Issuing the very same command again will execute iterations
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Nos. 3 and 4 on frame true. The net effect is the same as
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the one of REBIN/DECO observed seeing true 3,5 4