Jacques MALAPRADE Jacques MALAPRADE - 1 month ago 20
Python Question

Setting the limits on a colorbar in matplotlib

I have seen so many examples that just don't apply to my case. What I would like to do is set a simple minimum and maximum value for a colorbar. Setting a range for an image cmap is easy but this does not apply the same range to the minimum and maximum values of the colorbar.
The code below may explain:

triang = Triangulation(x,y)
plt.tricontourf(triang, z, vmax=1., vmin=0.)
plt.colorbar()


The colorbar is still fixed to the limits of the data z, although the cmap range is now fixed between 0 and 1.

Answer

I propose you incorporate you plot in a fig and get inspiration from this sample using the colorbar

data = np.tile(np.arange(4), 2)
fig = plt.figure()
ax = fig.add_subplot(121)
cax = fig.add_subplot(122)
cmap = colors.ListedColormap(['b','g','y','r'])
bounds=[0,1,2,3,4]
norm = colors.BoundaryNorm(bounds, cmap.N)
im=ax.imshow(data[None], aspect='auto',cmap=cmap, norm=norm)
cbar = fig.colorbar(im, cax=cax, cmap=cmap, norm=norm, boundaries=bounds, 
     ticks=[0.5,1.5,2.5,3.5],)
plt.show()

you see that you can set bounds for the colors in colorbar and ticks.

it is not rigourously what you want to achieve, but the hint to fig could help.

This other one uses ticks as well to define the scale of colorbar.

import numpy as np
import matplotlib.pyplot as plt

xi = np.array([0., 0.5, 1.0])
yi = np.array([0., 0.5, 1.0])
zi = np.array([[0., 1.0, 2.0],
               [0., 1.0, 2.0],
               [-0.1, 1.0, 2.0]])

v = np.linspace(-.1, 2.0, 15, endpoint=True)
plt.contour(xi, yi, zi, v, linewidths=0.5, colors='k')
plt.contourf(xi, yi, zi, v, cmap=plt.cm.jet)
x = plt.colorbar(ticks=v)
print x
plt.show()
Comments