Matplotlib fig.savefig(): The Great μ Conundrum – Sizing Issues in Vector Graphics

Introduction

Matplotlib, the beloved Python plotting library, is renowned for its flexibility and customization options. However, even the most seasoned developers can stumble upon peculiar issues. One such peculiarity is the misbehavior of the μ (mu) symbol in labels when saving figures to vector graphics using `fig.savefig()`. In this article, we’ll delve into the depths of this issue, explore its causes, and provide a comprehensive guide on how to tackle it.

The Problem: μ in Labels Gone Wrong

When creating plots with labels containing the μ symbol, you might notice that the font size and proportions are severely distorted after saving the figure to a vector graphic format like PDF, SVG, or EPS. This anomaly can be frustrating, especially when working with precise scientific or technical visualizations.

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([1, 2, 3])
ax.set_xlabel(r'$\mu$m')  # μ symbol in label

fig.savefig('mu_label_error.pdf')

Fig. 1: Distorted μ symbol in label after saving to PDF

Understanding the Root Cause

The issue stems from the way Matplotlib handles font rendering in vector graphics. When saving a figure, Matplotlib uses the TeX typesetting system to render mathematical expressions, including Greek symbols like μ. However, TeX has its own set of font metrics, which can lead to inconsistencies with the original font used in the plot.

Workarounds and Solutions

Fear not, dear reader! We’ve got you covered with a range of solutions to tackle this μ-sized problem:

Solution 1: Use Unicode Characters

Instead of using TeX notation (`r’$\mu$m’`) for the μ symbol, you can employ the Unicode character U+00B5 (μ) directly in your label string. This bypasses TeX rendering and preserves the original font metrics:

ax.set_xlabel('μm')  # Unicode character U+00B5

Fig. 2: Correct μ symbol in label using Unicode character

Solution 2: Specify Font Family and Size

By explicitly setting the font family and size for the label, you can ensure consistency across different output formats:

ax.set_xlabel(r'$\mu$m', fontsize=12, family='DejaVu Sans')

Fig. 3: Correct μ symbol in label with specified font family and size

Solution 3: Use Matplotlib’s `usetex` Parameter

By setting `usetex=True` when creating the figure, you can enable Matplotlib’s TeX rendering mode. This will use the TeX fonts and metrics, ensuring consistency with vector graphics:

import matplotlib
matplotlib.rcParams['text.usetex'] = True

fig, ax = plt.subplots()
ax.set_xlabel(r'$\mu$m')
fig.savefig('mu_label_usetex.pdf')

Fig. 4: Correct μ symbol in label using usetex parameter

Solution 4: Post-processing with Fonts

If you’re comfortable with command-line tools and font manipulation, you can use the `pdftops` utility to fix the font rendering after saving the figure:

pdftops -eps mu_label_error.pdf mu_label_fixed.eps

This method requires installing the `pdftops` tool and may require additional font configurations.

Conclusion

The μ symbol’s misbehavior in Matplotlib’s `fig.savefig()` can be overcome with a combination of creativity and technical finesse. By understanding the underlying causes and employing the workarounds outlined above, you can ensure precise and visually appealing plots in vector graphics.

Remember, when working with Matplotlib, it’s essential to stay vigilant and adapt to the intricacies of font rendering. With practice and patience, you’ll master the art of creating stunning, distortion-free plots that showcase your μ-umental skills!

Additional Resources

• Matplotlib’s Math Text Tutorial
• TeX Typesetting System
• Unicode Character U+00B5 (μ)

Solution	Advantages	Disadvantages
Unicode Characters	Easiest to implement, no additional dependencies	Limited to Unicode characters, may not work with all fonts
Specify Font Family and Size	Provides explicit control over font rendering	Requires font knowledge, may not work with all plots
Use Matplotlib’s `usetex` Parameter	Enables TeX rendering, consistent with vector graphics	Requires TeX installation, may slow down rendering
Post-processing with Fonts	Offers precise font control, flexible solution	Requires command-line tools, font knowledge, and configuration

By mastering the nuances of Matplotlib’s `fig.savefig()` and employing these solutions, you’ll be well on your way to creating stunning, μ-precise plots that impress!

Frequently Asked Question

Get the scoop on Matplotlib’s fig.savefig() and those pesky μ labels!