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 the cmap1 intensity index (0.0-1.0) 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.

       If RGB colors are provided then the interpolation takes place in RGB space and is trivial. However if HLS
       colors  are  provided then, because of the circular nature of the color wheel for the hue coordinate, the
       interpolation could be performed in either direction around the color wheel. The default behaviour is for
       the hue to be linearly interpolated ignoring this circular property of hue. So for example,  the  hues  0
       (red) and 240 (blue) will get interpolated via yellow, green and cyan. If instead you wish to interpolate
       the  other  way  around  the color wheel you have two options. You may provide hues outside the range [0,
       360), so by using a hue of -120 for blue or 360 for red  the  interpolation  will  proceed  via  magenta.
       Alternatively  you can utilise the alt_hue_path variable to reverse the direction of interpolation if you
       need to provide hues within the [0-360) range.

       Examples of interpolation  Huealt_hue_pathcolor  scheme[120  240]falsegreen-cyan-blue[240  120]falseblue-
       cyan-green[120   -120]falsegreen-yellow-red-magenta-blue[240   480]falseblue-magenta-red-yellow-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, and 21.

ARGUMENTS

       itype (PLBOOL(3plplot), input)
              true: RGB, false: HLS.

       npts (PLINT(3plplot), input)
              number of control points

       intensity (PLFLT_VECTOR(3plplot), input)
              A vector containing the cmap1 intensity index (0.0-1.0) in ascending order for each control point.

       coord1 (PLFLT_VECTOR(3plplot), input)
              A vector containing the first coordinate (H or R) for each control point.

       coord2 (PLFLT_VECTOR(3plplot), input)
              A vector containing the second coordinate (L or G) for each control point.

       coord3 (PLFLT_VECTOR(3plplot), input)
              A vector containing the third coordinate (S or B) for each control point.

       alt_hue_path (PLBOOL_VECTOR(3plplot), input)
              A  vector  (with  npts  -  1  elements),  each  containing  either  true  to  use the reversed HLS
              interpolation or false to use the regular  HLS  interpolation.   (alt_hue_path[i]  refers  to  the
              interpolation interval between the i and i + 1 control points). This parameter is not used for RGB
              colors (itype = true).

AUTHORS

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

SEE ALSO

       PLplot documentation at http://plplot.org/documentation.php.

                                                 February, 2020                               PLSCMAP1L(3plplot)