Saving Matplotlib plots to file


Martin McBride, 2022-06-10
Tags function plot file png
Categories matplotlib numpy

The previous article showed how to create a using NumPy.

We used the show function to display the plot in the Matplotlib viewer. However, it is often useful to save the image as a PNG file. In this section, we will look at some ways to do this.

Using the display window

In the previous article, we used the Matplotlib plt.show function to display a plot. The result is a window something like this:

This window has a save button (circled in red) that allows us to save the image in various formats, including PNG, JPEG, and PDF formats. The save dialog uses the full names (Portable Network Graphics, Joint Photographic Experts Group, and Portable Document Format) which can be a little confusing if you only know the formats by their acronyms.

Generating an image file in code

We can save a plot as an image file, simply by calling plt.savefig function:

from matplotlib import pyplot as plt
import math

xa = []
ya = []

for i in range(100):
    xa.append(i*12/100)

for x in xa:
    ya.append(math.sin(x)*math.exp(-x/4))

plt.plot(xa, ya)
plt.savefig("simple-function.png")

We call savefig instead of save, passing the file path where we want the file to be stored.

By default, the extension of the filepath selects the type of file created. Some common options are:

  • .png for a PDF image file (as used in the example).
  • .jpg for a JPEG image file.
  • .svg for an SVG vector graphics file.
  • .pdf for an PDF document.

There are a few other types supported, and the savefig function has some optional parameters to control other aspects of the output image (such as the resolution). We won't go through them here as they are quite specialised, but you can refer to the Matplotlib site for more details.

If you found this article useful, you might be interested in the course Introduction to Matplotlib by the same author.

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