CODEWITHSUNDEEP
pythonmatplotlibtransparencyalpha-transparency
Gabriel
Gabriel

Reputation: 42459

Transparent background with matplotlib's set_title()

I need to draw a title for a plot using set_title(), where its background shows with some degree of transparency.

I've tried three methods (one taken from this answer) but none seems to work. They either make the font of the text or the edges transparent, but not the background itself.

MWE:

import matplotlib.pyplot as plt

fig, ax = plt.subplots(1)
ax.minorticks_on()
ax.grid(b=True, which='minor', color='k', linestyle='--', lw=0.5,
        zorder=1)

# Method 1
ax.set_title("Title", x=0.5, y=0.92, fontsize=13, alpha=0.2,
             bbox=dict(facecolor='none'))

# Method 2
# ax.set_title("Title", x=0.5, y=0.92, fontsize=13,
#              bbox=dict(facecolor='none', alpha=0.2))

# Method 3
# t = ax.set_title("Title", x=0.5, y=0.92, fontsize=13)
# t.set_bbox(dict(facecolor='none', alpha=0.2, edgecolor='k'))

plt.savefig('test.png')

Output:

enter image description here

Upvotes: 2

Views: 3753

Answers (1)

tmdavison
tmdavison

Reputation: 69223

You were almost there. The issue is that you have facecolor='none', so even with an alpha set, there is nothing to make transparent, and you don't see the background at all.

You can change this by setting facecolor='white', for example, modifying your "Method 2":

ax.set_title("Title", x=0.5, y=0.92, fontsize=13,
             bbox=dict(facecolor='white', alpha=0.5))

enter image description here

This has the side-effect of also making the black border transparent too.

A way to fix that issue is to explicitly define the facecolor and edgecolor as (R,G,B,A) tuples, and make sure the edgecolor has alpha=1:

ax.set_title("Title", x=0.5, y=0.92, fontsize=13,
             bbox=dict(facecolor=(1,1,1,0.5),edgecolor=(0,0,0,1)))

enter image description here

Upvotes: 6

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