Joe Bathelt Joe Bathelt - 3 months ago 73
Python Question

Adjusting gridlines and ticks in matplotlib imshow

I'm trying to plot a matrix of values and would like to add gridlines to make the boundary between values clearer.
Unfortunately, imshow decided to locate the tick marks in the middle of each voxel. Is it possible to

a) remove the ticks but leave the label in the same location and

b) add gridlines between the pixel boundaries?

import matplotlib.pyplot as plt
import numpy as np

im = plt.imshow(np.reshape(np.random.rand(100), newshape=(10,10)),
interpolation='none', vmin=0, vmax=1, aspect='equal');
ax = plt.gca();
ax.set_xticks(np.arange(0, 10, 1));
ax.set_yticks(np.arange(0, 10, 1));
ax.set_xticklabels(np.arange(1, 11, 1));
ax.set_yticklabels(np.arange(1, 11, 1));


Image without the gridline and with tick marks in the wrong location
enter image description here

ax.grid(color='w', linestyle='-', linewidth=2)


Image with gridlines in the wrong location:

enter image description here

Answer

Try to shift axises' ticks:

ax.set_xticks(np.arange(-.5, 10, 1));
ax.set_yticks(np.arange(-.5, 10, 1));
ax.set_xticklabels(np.arange(1, 12, 1));
ax.set_yticklabels(np.arange(1, 12, 1));

enter image description here