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, 2016                       PLSCMAP1L(3plplot)