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NAME

       plscmap1l - Set cmap1 colors using a piece-wise linear relationship

SYNOPSIS

       plscmap1l(itype, npts, intensity, coord1, coord2, coord3, alt_hue_path)

DESCRIPTION

       Set  cmap1 colors using a piece-wise linear relationship between intensity index (from 0. to 1.) of cmap1
       and position in HLS or RGB color space (see the PLplot documentation).  May be called at any time.

       The idea here is to specify a number of control points  that  define  the  mapping  between  input  cmap1
       intensity  indices  and   HLS (or RGB).  Between these points, linear interpolation is used which gives a
       smooth variation of color with intensity index.  Any number of control points may be  specified,  located
       at  arbitrary  positions, although typically 2 - 4 are enough. Another way of stating this is that we are
       traversing a given number of lines through HLS (or RGB) space as we move through cmap1 intensity indices.
       The  control  points  at  the minimum and maximum position (0 and 1) must always be specified.  By adding
       more control points you can get more variation.  One good technique  for  plotting  functions  that  vary
       about some expected average is to use an additional 2 control points in the center (position ~= 0.5) that
       are the same lightness as the background (typically white for paper output, black for crt), and same  hue
       as the boundary control points.  This allows the highs and lows to be very easily distinguished.

       Each control point must specify the cmap1 intensity index and the associated  three coordinates in HLS or
       RGB space.  The first point must correspond to position = 0, and the last to position = 1.

       The default behaviour is for the hue to be linearly interpolated  between the control points.  Since  the
       hue  lies  in  the range [0, 360] this corresponds to interpolation around the "front" of the color wheel
       (red<->green<->blue<->red). If alt_hue_path[i] is true, then an alternative interpolation is used between
       control  points  i  and i+1. If  hue[i+1]-hue[i] > 0 then interpolation is between  hue[i] and hue[i+1] -
       360, otherwise  between hue[i] and hue[i+1] + 360.  You can consider this  as  interpolation  around  the
       "back"  or  "reverse"  of   the  color  wheel.  Specifying  alt_hue_path=NULL  is  equivalent  to setting
       alt_hue_path[] = false for  every control point.

       Examples of interpolation  Huealt_hue_pathcolor  scheme[120  240]falsegreen-cyan-blue[240  120]falseblue-
       cyan-green[120 240]truegreen-yellow-red-magenta-blue[240 120]trueblue-magenta-red-yellow-green

       Bounds     on     coordinatesRGBR[0,     1]magnitudeRGBG[0,    1]magnitudeRGBB[0,    1]magnitudeHLShue[0,
       360]degreesHLSlightness[0, 1]magnitudeHLSsaturation[0, 1]magnitude

       Redacted form: plscmap1l(itype, intensity, coord1, coord2, coord3, alt_hue_path)

       This function is used in examples 8,11,12,15,20,21.

ARGUMENTS

       itype (PLBOOL, input)
              true: RGB, false: HLS.

       npts (PLINT, input)
              number of control points

       intensity (const PLFLT *, input)
              intensity index for each control point (between 0.0 and 1.0, in ascending order)

       coord1 (const PLFLT *, input)
              first coordinate (H or R) for each control point

       coord2 (const PLFLT *, input)
              second coordinate (L or G) for each control point

       coord3 (const PLFLT *, input)
              third coordinate (S or B) for each control point

       alt_hue_path (const PLBOOL *, input)
              alternative interpolation method flag for each control  point.   (alt_hue_path[i]  refers  to  the
              interpolation interval between the i and i + 1 control points).

AUTHORS

       Many  developers  (who  are  credited  at  http://plplot.sourceforge.net/credits.php) have contributed to
       PLplot over its long history.

SEE ALSO

       PLplot documentation at http://plplot.sourceforge.net/documentation.php.

                                                 February, 2014                               PLSCMAP1L(3plplot)