1 MAKE_BACK Compute the  background intensity of an input image
        MAKE_BACK

    Computes the background image of an input image using a thresholding and
    a smoothing algorithm based on the conjugate gradient method.  The back-
    ground image is computed as follows
      -  First  the  image  is thresholded between THRESHOLD$[1] and THRESH-
        OLD$[2].  All pixels outside this range are blanked.
      - Then the image is smoothed using the conjugate gradient method, with
        NITER$  iterations and a smoothing parameter P$.  Blanked pixels are
        thus interpolated in the process.

    The output image is the background image.  P$ should be large enough  to
    yield  some smoothing (1 to 100, try...), and NITER$ also to assure con-
    vergence especially in "blanked" areas (NITER$ = 20 is typical).
2 P$
        TASK\REAL "Smoothing parameter" P$

    Smoothing parameter for the background.  Use 1 to 100
2 NITER$
        TASK\INTEGER "Number of smoothing iterations" NITER$

    NITER$ must be large enough to interpolate values  properly  in  blanked
    areas.  Use 10 to 30.

2 IN$
        TASK\CHARACTER "Input file name" IN$

    Input image (not modified)
2 OUT$
        TASK\CHARACTER "Output file name" OUT$

    Output background image name (created)
2 THRESHOLD$
        TASK\REAL "Low, high threshold, and guess" THRESHOLD$[3]

    Three  values  indicating  the  lowest significant background value, the
    highest, and an initial guess for blanked pixels.  THRESHOLD$[3]  should
    usually  be either equal to THRESHOLD$[2] or to THRESHOLD$[1], depending
    whether the signal is positive or negative...

1 ENDOFHELP
























