How to render math symbols as text in SVG/EPS/PDF images?

Question

When creating graphs using, for instance, Python. It is possible to save these figures as vector graphics (SVG, EPS, PDF) and the text is rendered separately. This makes it possible to select or search the text when shown in a pdf file. However, I've tried to render a simple graph using math symbols in addition to text (in latex). The math symbol gets encoded as part of the image, rather than as text.

Here is a minimum reproducible example.

import numpy as np
import matplotlib.pyplot as plt

x_list = np.linspace(-10,10,num=128)

y = list(map(lambda x: (x**2 + x + 1), x_list))

plt.plot(y, label="$\\Psi_{example}$")
plt.legend()
plt.xticks(np.linspace(0, 128, num=8),
            map(round, np.linspace(-10, 10, num=8), [0] * 8))

plt.savefig("./example.pdf")

Which produces the following image.

When saving this image as vector graphics, all the numbers as well as the 'example' word in the legend become selectable/searchable (i.e. rendered as text). However, the Ψ (Psi) character is not selectable/searchable.

Is there any way to make math symbols render as text in vector graphics?

Answer 1

I have been able to get it to work in the way I think you want by first installing a LaTeX distribution (I used MikTex, from here) and then setting the matpotlib option to use LaTeX to render your symbols and text.

Note that after installing MikTex, I had to open a new instance of my command prompt or code editor to make sure it was aware of the change to my PATH and where the LaTex is installed.

I added the import and mpl.rcParams line to your example:

import numpy as np
import matplotlib.pyplot as plt
import matplotlib as mpl

mpl.rcParams['text.usetex'] = True
x_list = np.linspace(-10, 10, num=128)

y = list(map(lambda x: (x**2 + x + 1), x_list))

plt.plot(y, label="$\\Psi_{example}$")
plt.legend()
plt.xticks(np.linspace(0, 128, num=8),
            map(round, np.linspace(-10, 10, num=8), [0] * 8))

plt.savefig("./example.pdf")