Thanks very much for the help. I have made some progress, but am still
having difficulties.
I wrote a function called make_solid_cmap (see test program below) that
takes a colormap name, a list of thresholds, and a list of colors as
inputs, and produces and registers a solid-color colormap. In the test
program, I attempt to create a solid-color colormap containing the
colors red, yellow, green, and blue.
Problem #1: When I use this colormap (in another piece of code that's
not shown), the result is a series of shades of gray.
Problem #2: The test program attempts to retrieve and display all
registered colormaps, but the one that I created in the test program
does not appear in the figure.
Phillip
### Start of code ###
from matplotlib import *
import matplotlib.pyplot as pyplot
from numpy import linspace, outer
from pylab import *
# Section 1: Define function for generating solid-color colormaps.
def make_solid_cmap(cmap_name, colors, thresholds=None):
"""Use list of colors (names or RGB tuples) and list of thresholds to
create
a solid-color colormap."""
# name_to_rgb converts a color name (string) to an RGB 3-tuple:
from webcolors import name_to_rgb
print 'len(colors)= ', len(colors)
if not isinstance(colors,list) or len(colors)<2:
raise Exception, 'colors must be a list of length 2 or greater.'
if thresholds is None:
# Assign default set of uniformly-spaced thresholds:
thresholds= linspace(0.0, 1.0, len(colors)+1)[1:-1]
else:
if not isinstance(thresholds,list):
raise Exception, 'thresholds must be a list.'
print 'thresholds= ', thresholds
if not isinstance(cmap_name,str) or len(cmap_name)==0:
raise Exception, 'cmap_name must be a non-null string.'
if len(colors)!=len(thresholds)+1:
raise Exception, 'The list of colors must be one longer than the
list ' \
'of thresholds.'
for i in range(len(colors)):
# If the ith color is specified via a name, replace the string
with an RGB
# 3-tuple:
if isinstance(colors[i],str): colors[i]= name_to_rgb(colors[i])
# If all three components of the tuple are ints, normalize by 256. to
# obtain floats in [0,1):
if isinstance(colors[i][0],int) and isinstance(colors[i][1],int) and \
isinstance(colors[i][2],int):
colors[i]= (colors[i][0]/256., colors[i][1]/256.,
colors[i][2]/256.)
# For each of the three RGB components, create initial empty list:
red_list= green_list= blue_list= []
# Each list will consist of a series of 3-tuples. The components of each
# 3-tuple are the threshold value, y0, and y1. The threshold in the
first
# tuple is always zero, and the second component of the first tuple is
# ignored, so we can set it to zero as well.
red_list .append( (0.0 , 0.0, colors[0][0] ) )
green_list .append( (0.0 , 0.0, colors[0][1] ) )
blue_list .append( (0.0 , 0.0, colors[0][2] ) )
for i in range(len(thresholds)):
red_list .append( (thresholds[i], colors[i][0], colors[i+1][0]) )
green_list.append( (thresholds[i], colors[i][1], colors[i+1][1]) )
blue_list .append( (thresholds[i], colors[i][2], colors[i+1][2]) )
red_list .append( (1.0 , colors[-1][0], 0.0 ) )
green_list .append( (1.0 , colors[-1][1], 0.0 ) )
blue_list .append( (1.0 , colors[-1][2], 0.0 ) )
cmap= matplotlib.colors.LinearSegmentedColormap(cmap_name, {
'red' : tuple(red_list),
'green': tuple(green_list),
'blue' : tuple(blue_list)
} )
pyplot.register_cmap(cmap=cmap)
# Section 2: Create and register a solid-color colormap containing red,
yellow,
# green, and blue (in that order):
make_solid_cmap('rygb', ['red','yellow','green','blue'])
# Section 3: Display all registered colormaps.
close(1)
rc('text', usetex=False)
a=outer(arange(0,1,0.01),ones(10))
fig= pyplot.figure(figsize=(13,7), dpi=120, facecolor=[1,1,1])
subplots_adjust(top=0.8,bottom=0.05,left=0.01,right=0.99)
maps=[m for m in cm.datad.keys() if not m.endswith("_r")]
maps.sort()
l=len(maps)+1
i=1
for m in maps:
print m
subplot(1,l,i)
axis("off")
imshow(a,aspect='auto',cmap=get_cmap(m),origin="lower")
title(m,rotation=90,fontsize=18)
i=i+1
show()
Eric Firing wrote:
Dr. Phillip M. Feldman wrote:
I'd like to be able to create and use a custom colormap. I'm
creating the
colormap via
the following statement:
matplotlib.colors.ListedColormap([(0,0,0),(0.6,0,0),(0,0.6,0),(0.6,0.6,0)],
name='Earth')
Assign it to a variable, like
earth_cmap = matplotlib.colors.ListedColormap(
[(0,0,0),(0.6,0,0),(0,0.6,0),(0.6,0.6,0)],
name='Earth')
and then use cmap=earth_cmap as your kwarg specification.
The ability to register user-generated cmaps so that they can be
retrieved via get_cmap is very new, and not present in 0.98.5. It is
in the latest release (0.99.1), though. You would need to use the
register_cmap function.
Eric
The above statement appears to work, but when I attempt to use this
colormap, I
get the error shown below. Any suggestions will be appreciated.
AssertionError Traceback (most recent call
last)
art.py in <module>()
253
254 # Plot z as image using specified color map:
--> 255 pyplot.imshow(z, origin='lower',
cmap=get_cmap(map_names[n_map-1]),
256 extent=[x.min(),x.max(),y.min(),y.max()])
257
C:\Program
Files\Python25\lib\site-packages\matplotlib-0.98.5.2n2-py2.5-win32.egg\matplotlib\cm.pyc
in get_cmap(name, lut)
19 if lut is None: lut = mpl.rcParams['image.lut']
20
---> 21 assert(name in datad.keys())
22 return colors.LinearSegmentedColormap(name, datad[name],
lut)
23
AssertionError:
------------------------------------------------------------------------------
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