1PLSCMAP1L(3plplot) PLplot API PLSCMAP1L(3plplot)
2
6 plscmap1l - Set cmap1 colors using a piece-wise linear relationship
7
9 plscmap1l(itype, npts, intensity, coord1, coord2, coord3, alt_hue_path)
10
12 Set cmap1 colors using a piece-wise linear relationship between the
13 cmap1 intensity index (0.0-1.0) and position in HLS or RGB color space
14 (see the PLplot documentation). May be called at any time.
15 The idea here is to specify a number of control points that define the
17 mapping between input cmap1 intensity indices and HLS or RGB. Between
18 these points, linear interpolation is used which gives a smooth varia‐
19 tion of color with intensity index. Any number of control points may
20 be specified, located at arbitrary positions, although typically 2 - 4
21 are enough. Another way of stating this is that we are traversing a
22 given number of lines through HLS or RGB space as we move through cmap1
23 intensity indices. The control points at the minimum and maximum posi‐
24 tion (0 and 1) must always be specified. By adding more control points
25 you can get more variation. One good technique for plotting functions
26 that vary about some expected average is to use an additional 2 control
27 points in the center (position ~= 0.5) that are the same lightness as
28 the background (typically white for paper output, black for crt), and
29 same hue as the boundary control points. This allows the highs and
30 lows to be very easily distinguished.
31 Each control point must specify the cmap1 intensity index and the asso‐
33 ciated three coordinates in HLS or RGB space. The first point must
34 correspond to position = 0, and the last to position = 1.
35 If RGB colors are provided then the interpolation takes place in RGB
37 space and is trivial. However if HLS colors are provided then, because
38 of the circular nature of the color wheel for the hue coordinate, the
39 interpolation could be performed in either direction around the color
40 wheel. The default behaviour is for the hue to be linearly interpolated
41 ignoring this circular property of hue. So for example, the hues 0
42 (red) and 240 (blue) will get interpolated via yellow, green and cyan.
43 If instead you wish to interpolate the other way around the color wheel
44 you have two options. You may provide hues outside the range [0, 360),
45 so by using a hue of -120 for blue or 360 for red the interpolation
46 will proceed via magenta. Alternatively you can utilise the
47 alt_hue_path variable to reverse the direction of interpolation if you
48 need to provide hues within the [0-360) range.
49 Examples of interpolation Huealt_hue_pathcolor scheme[120 240]falseg‐
51 reen-cyan-blue[240 120]falseblue-cyan-green[120 -120]falsegreen-yellow-
52 red-magenta-blue[240 480]falseblue-magenta-red-yellow-green[120
53 240]truegreen-yellow-red-magenta-blue[240 120]trueblue-magenta-red-yel‐
54 low-green
55 Bounds on coordinatesRGBR[0, 1]magnitudeRGBG[0, 1]magnitudeRGBB[0,
57 1]magnitudeHLShue[0, 360]degreesHLSlightness[0, 1]magnitudeHLSsatura‐
58 tion[0, 1]magnitude
59 Redacted form: plscmap1l(itype, intensity, coord1, coord2, coord3,
61 alt_hue_path)
62 This function is used in examples 8, 11, 12, 15, 20, and 21.
64
66 itype (PLBOOL(3plplot), input)
67 true: RGB, false: HLS.
68 npts (PLINT(3plplot), input)
70 number of control points
71 intensity (PLFLT_VECTOR(3plplot), input)
73 A vector containing the cmap1 intensity index (0.0-1.0) in as‐
74 cending order for each control point.
75 coord1 (PLFLT_VECTOR(3plplot), input)
77 A vector containing the first coordinate (H or R) for each con‐
78 trol point.
79 coord2 (PLFLT_VECTOR(3plplot), input)
81 A vector containing the second coordinate (L or G) for each con‐
82 trol point.
83 coord3 (PLFLT_VECTOR(3plplot), input)
85 A vector containing the third coordinate (S or B) for each con‐
86 trol point.
87 alt_hue_path (PLBOOL_VECTOR(3plplot), input)
89 A vector (with npts - 1 elements), each containing either true
90 to use the reversed HLS interpolation or false to use the regu‐
91 lar HLS interpolation. (alt_hue_path[i] refers to the interpo‐
92 lation interval between the i and i + 1 control points). This
93 parameter is not used for RGB colors (itype = true).
94
97 Many developers (who are credited at http://plplot.org/credits.php)
98 have contributed to PLplot over its long history.
99
101 PLplot documentation at http://plplot.org/documentation.php.
102 August, 2021 PLSCMAP1L(3plplot)