I have integers ranging from 0 to 10000. I want to map a color to each of these. Then based on the integer value i want to retrieve RGB equivalent of the color corresponding to integer value. Basically i want to have an interpolation effect between two or more colors e.g. if the colors are green and red,then green having least weight(0) and red having having highest weight (10000). how can i implement this mapping using matplotlib or is there any other library for the same.
2 Answers
It is indeed possible to sample 10000 colors from a given colormap:
#!/usr/bin/python3
from numpy import arange
from matplotlib import pyplot as plt
from matplotlib import cm
from matplotlib.colors import LinearSegmentedColormap
# ======
## data:
N = 10000
data = arange(N +1)
# =================
## custom colormap:
# red-green colormap:
cdict = {'red': [(0.0, 1.0, 1.0), # red decreases
(1.0, 0.0, 0.0)],
'green': [(0.0, 0.0, 0.0), # green increases
(1.0, 1.0, 1.0)],
'blue': [(0.0, 0.0, 0.0), # no blue at all
(1.0, 0.0, 0.0)]}
red_green_cm = LinearSegmentedColormap('RedGreen', cdict, N)
# ======
## plot:
colors = cm.get_cmap(red_green_cm, N)
fig = plt.figure()
ax = fig.add_subplot(111)
# each line is of its own color:
for i, x in enumerate(data):
ax.plot(data, data*x, color=colors(i))
fig.savefig("red-green-cm.png")
Result:
Edit
One can also add a colorbar:
#!/usr/bin/python3
from numpy import arange
import matplotlib as mpl
from matplotlib import pyplot as plt
from matplotlib import cm
from matplotlib.colors import LinearSegmentedColormap
# ======
## data:
N = 10000
data = arange(N +1)
# =================
## custom colormap:
# red-green colormap:
cdict = {'red': [(0.0, 1.0, 1.0), # red decreases
(1.0, 0.0, 0.0)],
'green': [(0.0, 0.0, 0.0), # green increases
(1.0, 1.0, 1.0)],
'blue': [(0.0, 0.0, 0.0), # no blue at all
(1.0, 0.0, 0.0)] }
red_green_cm = LinearSegmentedColormap('RedGreen', cdict, N)
# ======
## plot:
colors = cm.get_cmap(red_green_cm, N)
fig = plt.figure()
ax = fig.add_subplot(111)
# each line is of its own color:
for i, x in enumerate(data):
ax.plot(data, data*x, color=colors(i))
# make space for colorbar:
fig.tight_layout(rect=[0, 0, 0.85, 1])
# adding colorbar:
ax_cb = fig.add_axes([0.85, 0.10, 0.05, 0.8])
norm = mpl.colors.Normalize(vmin=data[0], vmax=data[-1])
cb = mpl.colorbar.ColorbarBase(ax_cb, cmap=red_green_cm, norm=norm, orientation='vertical')
fig.savefig("red-green-cm.png")
Comments
A colormap that ranges between two-extremes is called Diverging and there's a RdYlGn (red-yellow-green) colormap in matplotlib that does exactly what you want. Take a look at the colormaps reference. I don't know whether the range is 0 to 10,000 though it surely handles 0 to 100 and you could map your range into that.
1 Comment
mwaskom
If the data range from 0 to 10000, it suggests that a sequential palette is more appropriate, although it's hard to know for sure without knowing more about the nature of the data.