Adjusting Text background transparency

Question

I'm trying to put some text with a background on a matplotlib figure, with the text and background both transparent. The following code

import numpy as np
import matplotlib.pyplot as plt
plt.figure()
ax = plt.subplot(111)
plt.plot(np.linspace(1,0,1000))
t = plt.text(0.03,.95,'text',transform=ax.transAxes,backgroundcolor='0.75',alpha=.5)
plt.show()

makes the text semi-transparent relative to the text's background, but the background isn't at all transparent relative to the line it obscures in the figure.

t.figure.set_alpha(.5)

and

t.figure.patch.set_alpha(.5)

also don't do the trick.

Solution

The alpha passed to plt.text() will change the transparency of the text font. To change the background you have to change the alpha using Text.set_bbox():

t = plt.text(0.5, 0.5, 'text', transform=ax.transAxes, fontsize=30)
t.set_bbox(dict(facecolor='red', alpha=0.5, edgecolor='red'))
#changed first dict arg from "color='red'" to "facecolor='red'" to work on python 3.6

Comments

[endolith]

You can also do props = dict(...) and ax.text(... bbox=props)