def _parse_color_segments(segments, name, hinge=0, colormodel='RGB', N=256):
"""
A private function to parse color segments.
Parameters
----------
segments : list
A list of segments following the GMT structure:
`z0 color0 z1 color1`
Where color is either a named color from the GMT color list like
`black` or `r g b` or `r/g/b`.
name : str, optional
name of the returned cmap.
hinge : float, optional
Zero by default.
colormodel : str, optional
Assumed to be ``'RGB'`` by default.
N : int, optional
Number of entries in the look-up-table of the colormap.
Returns
-------
cmap : Colormap
Either a LinearSegmentedColormap if sequential or
DynamicColormap if diverging around a ``hinge`` value.
"""
x = []
r = []
g = []
b = []
for segment in segments:
# parse the left side of each segment
fields = re.split(r'\s+|[/]', segment)
x.append(float(fields[0]))
try:
r.append(float(fields[1]))
g.append(float(fields[2]))
b.append(float(fields[3]))
xi = 4
except ValueError:
r_, g_, b_ = GMT_COLOR_NAMES[fields[1]]
r.append(float(r_))
g.append(float(g_))
b.append(float(b_))
xi = 2
# parse the right side of the last segment
x.append(float(fields[xi]))
try:
r.append(float(fields[xi + 1]))
g.append(float(fields[xi + 2]))
b.append(float(fields[xi + 3]))
except ValueError:
r_, g_, b_ = GMT_COLOR_NAMES[fields[-1]]
r.append(float(r_))
g.append(float(g_))
b.append(float(b_))
x = np.array(x)
r = np.array(r)
g = np.array(g)
b = np.array(b)
if colormodel == "HSV":
for i in range(r.shape[0]):
# convert HSV to RGB
rr, gg, bb = hsv_to_rgb([r[i] / 360., g[i], b[i]])
r[i] = rr
g[i] = gg
b[i] = bb
elif colormodel == "RGB":
r /= 255.
g /= 255.
b /= 255.
else:
raise ValueError('Color model `{}` not understood'.format(colormodel))
if hinge is not None and x[0] < hinge < x[-1]:
cmap_type = 'dynamic'
norm = TwoSlopeNorm(vmin=x[0], vcenter=hinge, vmax=x[-1])
hinge_index = np.abs(x - hinge).argmin()
else:
cmap_type = 'normal'
hinge = None
norm = Normalize(vmin=x[0], vmax=x[-1])
xNorm = norm(x)
red = []
blue = []
green = []
for i in range(xNorm.size):
# avoid interpolation across the hinge
try:
if i == (hinge_index):
red.append([xNorm[i], r[i - 1], r[i]])
green.append([xNorm[i], g[i - 1], g[i]])
blue.append([xNorm[i], b[i - 1], b[i]])
except UnboundLocalError:
pass
red.append([xNorm[i], r[i], r[i]])
green.append([xNorm[i], g[i], g[i]])
blue.append([xNorm[i], b[i], b[i]])
# return colormap
cdict = dict(red=red, green=green, blue=blue)
cmap = LinearSegmentedColormap(name=name, segmentdata=cdict, N=N)
cmap.values = x
cmap.colors = list(zip(r, g, b))
cmap.hinge = hinge
cmap._init()
if cmap_type == 'dynamic':
return DynamicColormap(cmap)
else:
return cmap
