code: def cubehelix(gamma=1.0, s=0.5, r=-1.5, h=1.0):
      """
      Return custom data dictionary of (r, g, b) conversion functions, which can
      be used with :func:`register_cmap`, for the cubehelix color scheme.
  
      Unlike most other color schemes cubehelix was designed by D.A. Green to
      be monotonically increasing in terms of perceived brightness.
      Also, when printed on a black and white postscript printer, the scheme
      results in a greyscale with monotonically increasing brightness.
      This color scheme is named cubehelix because the (r, g, b) values produced
      can be visualised as a squashed helix around the diagonal in the
      (r, g, b) color cube.
  
      For a unit color cube (i.e. 3D coordinates for (r, g, b) each in the
      range 0 to 1) the color scheme starts at (r, g, b) = (0, 0, 0), i.e. black,
      and finishes at (r, g, b) = (1, 1, 1), i.e. white. For some fraction *x*,
      between 0 and 1, the color is the corresponding grey value at that
      fraction along the black to white diagonal (x, x, x) plus a color
      element. This color element is calculated in a plane of constant
      perceived intensity and controlled by the following parameters.
  
      Parameters
      ----------
      gamma : float, default: 1
          Gamma factor emphasizing either low intensity values (gamma < 1), or
          high intensity values (gamma > 1).
      s : float, default: 0.5 (purple)
          The starting color.
      r : float, default: -1.5
          The number of r, g, b rotations in color that are made from the start
          to the end of the color scheme.  The default of -1.5 corresponds to ->
          B -> G -> R -> B.
      h : float, default: 1
          The hue, i.e. how saturated the colors are. If this parameter is zero
          then the color scheme is purely a greyscale.
      """
      return {
          "red": partial(_ch_helper, gamma, s, r, h, -0.14861, 1.78277),
          "green": partial(
              _ch_helper, gamma, s, r, h, -0.29227, -0.90649
          ),
          "blue": partial(_ch_helper, gamma, s, r, h, 1.97294, 0.0),
      }
  
imports: from functools import partial
  import numpy
label_desc: Use image node_id 8 for calling a global function with example usage: cubehelix(gamma, s, r, h) and returns: dict