How to change imshow axis values (labels) in matplotlib ?

Examples of how to change imshow axis values (labels) in matplotlib:

Let's consider a simple figure using matplotlib imshow

import numpy as np
import matplotlib.pyplot as plt

def f(x,y):
    return (x+y)*np.exp(-5.0*(x**2+y**2))

x,y = np.mgrid[-1:1:100j, -1:1:100j]

z = f(x,y)

plt.imshow(z)

plt.colorbar()

plt.title('How to change imshow axis values with matplotlib ?', fontsize=8)

plt.savefig("imshow_change_values_on_axis_01.png", bbox_inches='tight')
plt.close()

By default, the x and y values corresponds to the indexes of the array used as an input in the imshow function:

Change imshow axis values using the option extent

To change the axis values, a solution is to use the extent option:

extent = [x_min , x_max, y_min , y_max]

for example

plt.imshow(z,extent=[-1,1,-1,1])

Customize the axis values using set_xticks() and set_yticks()

Another solution is to use the matplotlib functions set_xticks() and set_yticks(). Fo example, with the option extent set up to [-1,1,-1,1], it is possible to replace the values [-0.75,-0.25,0.25,0.75] by ['A2', 'B2', 'C2', 'D2']:

fig, ax = plt.subplots(1,1)

img = ax.imshow(z,extent=[-1,1,-1,1])

x_label_list = ['A2', 'B2', 'C2', 'D2']

ax.set_xticks([-0.75,-0.25,0.25,0.75])

ax.set_xticklabels(x_label_list)

fig.colorbar(img)

Without using the option extent, it is necessary to use the array indexes to specify where to replace the values:

fig, ax = plt.subplots(1,1)

img = ax.imshow(z)

x_label_list = ['A1', 'B1', 'C1', 'D1']

ax.set_xticks([20,40,60,80])

ax.set_xticklabels(x_label_list)

fig.colorbar(img)

Another example using set_xticks() and set_yticks():

fig, ax = plt.subplots(1,1)

img = ax.imshow(z,extent=[-1,1,-1,1])

x_label_list = ['x1', 'x2', 'x3', 'x4']
y_label_list = ['y1', 'y2', 'y3', 'y4']

ax.set_xticks([-0.75,-0.25,0.25,0.75])
ax.set_yticks([-0.75,-0.25,0.25,0.75])

ax.set_xticklabels(x_label_list)
ax.set_yticklabels(y_label_list)

fig.colorbar(img)

Code python to test imshow axis values (labels) in matplotlib

import numpy as np
import matplotlib.pyplot as plt

def f(x,y):
    return (x+y)*np.exp(-5.0*(x**2+y**2))

x,y = np.mgrid[-1:1:100j, -1:1:100j]

z = f(x,y)

plt.imshow(z)

plt.colorbar()

plt.title('How to change imshow axis values with matplotlib ?', fontsize=8)

plt.savefig("imshow_change_values_on_axis_01.png", bbox_inches='tight')
plt.close()

#----------------------------------------------------------------------------------------#

plt.imshow(z,extent=[-1,1,-1,1])

plt.colorbar()

plt.title('How to change imshow axis values with matplotlib ?', fontsize=8)

plt.savefig("imshow_change_values_on_axis_02.png", bbox_inches='tight')
plt.close()

#----------------------------------------------------------------------------------------#

fig, ax = plt.subplots(1,1)

img = ax.imshow(z)

x_label_list = ['A1', 'B1', 'C1', 'D1']

ax.set_xticks([20,40,60,80])

ax.set_xticklabels(x_label_list)

fig.colorbar(img)

plt.title('How to change imshow axis values with matplotlib ?', fontsize=8)

plt.savefig("imshow_change_values_on_axis_03.png", bbox_inches='tight')
plt.close()

#----------------------------------------------------------------------------------------#

fig, ax = plt.subplots(1,1)

img = ax.imshow(z,extent=[-1,1,-1,1])

x_label_list = ['A2', 'B2', 'C2', 'D2']

ax.set_xticks([-0.75,-0.25,0.25,0.75])

ax.set_xticklabels(x_label_list)

fig.colorbar(img)

plt.title('How to change imshow axis values with matplotlib ?', fontsize=8)

plt.savefig("imshow_change_values_on_axis_04.png", bbox_inches='tight')
plt.close()

#----------------------------------------------------------------------------------------#

fig, ax = plt.subplots(1,1)

img = ax.imshow(z,extent=[-1,1,-1,1])

x_label_list = ['x1', 'x2', 'x3', 'x4']
y_label_list = ['y1', 'y2', 'y3', 'y4']

ax.set_xticks([-0.75,-0.25,0.25,0.75])
ax.set_yticks([-0.75,-0.25,0.25,0.75])

ax.set_xticklabels(x_label_list)
ax.set_yticklabels(y_label_list)

fig.colorbar(img)

plt.title('How to change imshow axis values with matplotlib ?', fontsize=8)

plt.savefig("imshow_change_values_on_axis_05.png", bbox_inches='tight')
plt.close()

References