Merge pull request #468 from pschella/cubehelix

efiring · efiring · commit b0dcaa091ca6 · 2011-09-17T12:26:42.000-07:00
Added cubehelix monotonically increasing colorscheme (developed by D.A. G
diff --git a/lib/matplotlib/_cm.py b/lib/matplotlib/_cm.py
@@ -46,6 +46,68 @@
         'blue': lambda x: -1.1 * np.sin((x * 20.9) * np.pi),
 }
 
+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. 3-D 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.
+
+    Optional keyword arguments:
+
+      =========   =======================================================
+      Keyword     Description
+      =========   =======================================================
+      gamma       gamma factor to emphasise either low intensity values
+                  (gamma < 1), or high intensity values (gamma > 1);
+                  defaults to 1.0.
+      s           the start color; defaults to 0.5 (i.e. purple).
+      r           the number of r,g,b rotations in color that are made
+                  from the start to the end of the color scheme; defaults
+                  to -1.5 (i.e. -> B -> G -> R -> B).
+      h           the hue parameter which controls how saturated the
+                  colors are. If this parameter is zero then the color
+                  scheme is purely a greyscale; defaults to 1.0.
+      =========   =======================================================
+
+    """
+
+    def get_color_function(p0, p1):
+        def color(x):
+            # Apply gamma factor to emphasise low or high intensity values
+            xg = x**gamma
+
+            # Calculate amplitude and angle of deviation from the black
+            # to white diagonal in the plane of constant
+            # perceived intensity.
+            a = h * xg * (1 - xg) / 2
+
+            phi = 2 * np.pi * (s / 3 + r * x)
+
+            return xg + a * (p0 * np.cos(phi) + p1 * np.sin(phi))
+        return color
+
+    return {
+            'red': get_color_function(-0.14861, 1.78277),
+            'green': get_color_function(-0.29227, -0.90649),
+            'blue': get_color_function(1.97294, 0.0),
+    }
+
+_cubehelix_data = cubehelix()
+
 _bwr_data = ((0.0, 0.0, 1.0), (1.0, 1.0, 1.0), (1.0, 0.0, 0.0))
 _brg_data = ((0.0, 0.0, 1.0), (1.0, 0.0, 0.0), (0.0, 1.0, 0.0))
 
@@ -1575,6 +1637,7 @@ def gfunc32(x):
     'brg':    _brg_data,
     'cool':   _cool_data,
     'copper': _copper_data,
+    'cubehelix': _cubehelix_data,
     'flag':   _flag_data,
     'gnuplot': _gnuplot_data,
     'gnuplot2': _gnuplot2_data,
diff --git a/lib/matplotlib/cm.py b/lib/matplotlib/cm.py
@@ -13,6 +13,7 @@
 import matplotlib.colors as colors
 import matplotlib.cbook as cbook
 from matplotlib._cm import datad
+from matplotlib._cm import cubehelix
 
 cmap_d = dict()
 
