LUT

        [GTVL\]LUT [Argum] [/PEN] [/REVERSE]

    Modify  the bitmap or pen look up table. Option /PEN indicates to modify
    the value of the 16 user-controlled pen colors (colors 8 to  23)  rather
    than the bitmap look-up table.

    The default argument is LUT. Possibles arguments are:
    - ?
        Type  "LUT ?"  to display the list of available LUTs, or execute the
        demonstration procedure @ gag_demo:demo-luts.greg for  an  overview.
        One  can  use  alternatively  the  LUT editor (button "Edit Lut") to
        browse and edit the LUTs in an interactive widget.
    - DEFAULT
        Load the default color table.
    - COLOR
        Load a color table with a circular hue value, from red to red.
    - BLUERED
        Load a color table from dark blue to light blue, white,  light  red,
        dark red, suited for blueshift to redshift display.
    - BLACK
        Load  a  black  and  white  color  table  (white  background,  black
        sources).
    - WHITE, RED, GREEN, BLUE, MAGENTA, YELLOW, CYAN and NULL
        Load a color table with black background and sources in  the  corre-
        sponding color (NULL is fully black).
    - LUT
        Load  the  color table defined by an HSV (HUE, SATURATION and VALUE)
        or RGB (RED, GREEN and BLUE) color model. There are six  user-write-
        able  SIC  variables  named  LUT%HUE, LUT%SATURATION, LUT%VALUE, and
        LUT%RED, LUT%GREEN and LUT%BLUE that contain the HSV and  RGB  model
        of  the  current  LUT.  These arrays values can be manipulated using
        standard SIC mathematic functions to create new Look-Up Tables  (see
        below).  Depending  on the value on LUT%MODE, the model is read from
        the HSV (LUT%MODE.eq.1) or from the RGB (LUT%MODE.eq.2) arrays.
    - Any other LUT Argum will read Red Green Blue values from the formatted
        file named "Argum". See subtopic FILE for details.

    A convenient value for the hue array is
            LET LUT%HUE[I] = 256*(1-(I/LUT%SIZE))
            LET LUT%SATURATION 1
            LET LUT%VALUE 1
            LUT LUT
    which  is a "classical" color table from blue to red as used in AIPS for
    example. Color contours can be obtained using variations around the fol-
    lowing command:
            LET LUT%HUE[I] = 16*INT(256*(1-(I/LUT%SIZE))/16)
    and so on with the most funny functions you may invent.
    CAUTION: the hue is a real number between 0.0 and 360.0

    The  LUT,  whereever  it comes from, can be reverted before use with the
    option /REVERSE.

    Note that a similar behaviour is defined for  the  BLANKING  color  (the
    color  used  to  paint  blanked  pixels  in  images), with the six reals
    LUT%BLANK%HUE, LUT%BLANK%SATURATION, LUT%BLANK%VALUE, and LUT%BLANK%RED,
    LUT%BLANK%GREEN, LUT%BLANK%BLUE.