Matplotlib, controlling mark_inset() properties (kwargs)

Question

I am trying to make a plot with matplotlib with an inset zoom. I found the following example which will produce a plot with an inset:

import matplotlib.pyplot as plt

from mpl_toolkits.axes_grid1.inset_locator import zoomed_inset_axes
from mpl_toolkits.axes_grid1.inset_locator import mark_inset

import numpy as np


def get_demo_image():
    from matplotlib.cbook import get_sample_data
    import numpy as np
    f = get_sample_data("axes_grid/bivariate_normal.npy", asfileobj=False)
    z = np.load(f)
    # z is a numpy array of 15x15
    return z, (-3, 4, -4, 3)

fig, ax = plt.subplots(figsize=[5, 4])

# prepare the demo image
Z, extent = get_demo_image()
Z2 = np.zeros([150, 150], dtype="d")
ny, nx = Z.shape
Z2[30:30 + ny, 30:30 + nx] = Z

# extent = [-3, 4, -4, 3]
ax.imshow(Z2, extent=extent, interpolation="nearest",
          origin="lower")

axins = zoomed_inset_axes(ax, 6, loc=1)  # zoom = 6
axins.imshow(Z2, extent=extent, interpolation="nearest",
             origin="lower")

# sub region of the original image
x1, x2, y1, y2 = -1.5, -0.9, -2.5, -1.9
axins.set_xlim(x1, x2)
axins.set_ylim(y1, y2)

plt.xticks(visible=False)
plt.yticks(visible=False)

# draw a bbox of the region of the inset axes in the parent axes and
# connecting lines between the bbox and the inset axes area
mark_inset(ax, axins, loc1=2, loc2=4, fc="none", ec="0.5")

plt.draw()
plt.show()

However, I am having trouble finding the correct arguments to pass the mark_inset() function in order to make the linewidth of the boxing line thicker, or the color line red.

I could not find what the arguments fc and ec stand for either, by searching for the documentation.

Answer 1

Adding the following after the zoomed_inset_axes should do what you need:

axins = zoomed_inset_axes(ax, 6, loc=1) 

for axis in ['top','bottom','left','right']:
    axins.spines[axis].set_linewidth(3)
    axins.spines[axis].set_color('r')

To change the inset lines change as follows for red:

mark_inset(ax, axins, loc1=2, loc2=4, fc="none", lw=2, ec='r')

Giving you the following kind of output:

The Matplot lib defines fc and ec as follows for mark_inset :

• facecolor or fc - mpl color spec, or None for default, or 'none' for no color.
• edgecolor or ec - mpl color spec, or None for default, or 'none' for no color.