1PLSCMAP1L(3plplot) PLplot API PLSCMAP1L(3plplot)
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6 plscmap1l - Set cmap1 colors using a piece-wise linear relationship
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9 plscmap1l(itype, npts, intensity, coord1, coord2, coord3, alt_hue_path)
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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).
18 Between these points, linear interpolation is used which gives a smooth
19 variation of color with intensity index. Any number of control points
20 may be specified, located at arbitrary positions, although typically 2
21 - 4 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
23 cmap1 intensity indices. The control points at the minimum and maximum
24 position (0 and 1) must always be specified. By adding more control
25 points you can get more variation. One good technique for plotting
26 functions that vary about some expected average is to use an additional
27 2 control points in the center (position ~= 0.5) that are the same
28 lightness as the background (typically white for paper output, black
29 for crt), and same hue as the boundary control points. This allows the
30 highs and 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 The default behaviour is for the hue to be linearly interpolated
37 between the control points. Since the hue lies in the range [0, 360]
38 this corresponds to interpolation around the "front" of the color wheel
39 (red<->green<->blue<->red). If alt_hue_path[i] is true, then an alter‐
40 native interpolation is used between control points i and i+1. If
41 hue[i+1]-hue[i] > 0 then interpolation is between hue[i] and hue[i+1] -
42 360, otherwise between hue[i] and hue[i+1] + 360. You can consider this
43 as interpolation around the "back" or "reverse" of the color wheel.
44 Specifying alt_hue_path=NULL is equivalent to setting alt_hue_path[] =
45 false for every control point.
46 Examples of interpolation Huealt_hue_pathcolor scheme[120 240]falseg‐
48 reen-cyan-blue[240 120]falseblue-cyan-green[120 240]truegreen-yellow-
49 red-magenta-blue[240 120]trueblue-magenta-red-yellow-green
50 Bounds on coordinatesRGBR[0, 1]magnitudeRGBG[0, 1]magnitudeRGBB[0,
52 1]magnitudeHLShue[0, 360]degreesHLSlightness[0, 1]magnitudeHLSsatura‐
53 tion[0, 1]magnitude
54 Redacted form: plscmap1l(itype, intensity, coord1, coord2, coord3,
56 alt_hue_path)
57 This function is used in examples 8, 11, 12, 15, 20, and 21.
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61 itype (PLBOOL(3plplot), input)
62 true: RGB, false: HLS.
63 npts (PLINT(3plplot), input)
65 number of control points
66 intensity (PLFLT_VECTOR(3plplot), input)
68 A vector containing the cmap1 intensity index (0.0-1.0) in
69 ascending order for each control point.
70 coord1 (PLFLT_VECTOR(3plplot), input)
72 A vector containing the first coordinate (H or R) for each con‐
73 trol point.
74 coord2 (PLFLT_VECTOR(3plplot), input)
76 A vector containing the second coordinate (L or G) for each con‐
77 trol point.
78 coord3 (PLFLT_VECTOR(3plplot), input)
80 A vector containing the third coordinate (S or B) for each con‐
81 trol point.
82 alt_hue_path (PLBOOL_VECTOR(3plplot), input)
84 A vector (with npts - 1 elements) containing the alternative
85 interpolation method Boolean value for each control point inter‐
86 val. (alt_hue_path[i] refers to the interpolation interval
87 between the i and i + 1 control points).
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91 Many developers (who are credited at http://plplot.source‐
92 forge.net/credits.php) have contributed to PLplot over its long his‐
93 tory.
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96 PLplot documentation at http://plplot.sourceforge.net/documenta‐
97 tion.php.
98 August, 2017 PLSCMAP1L(3plplot)