How to Change Plot Background in Matplotlib

Introduction

Matplotlib is one of the most widely used data visualization libraries in Python. From simple to complex visualizations, it's the go-to library for most.

In this tutorial, we'll take a look at how to change the background of a plot in Matplotlib.

Importing Data and Libraries

Let's import the required libraries first. We'll obviously need Matplotlib, and we'll use Pandas to read the data:

import matplotlib.pyplot as plt
import pandas as pd

Specifically, we'll be using the Seattle Weather Dataset:

weather_data = pd.read_csv("seattleWeather.csv")
print(weather_data.head())

         DATE  PRCP  TMAX  TMIN  RAIN
0  1948-01-01  0.47    51    42  True
1  1948-01-02  0.59    45    36  True
2  1948-01-03  0.42    45    35  True
3  1948-01-04  0.31    45    34  True
4  1948-01-05  0.17    45    32  True

Creating a Plot

Now, let's create a simple Matplotlib Scatter Plot, with a few different variables we want to visualize:

PRCP = weather_data['PRCP']
TMAX = weather_data['TMAX']
TMIN = weather_data['TMIN']

Now, we'll construct a scatter plot between the minimum temperature and precipitation and show() it using Matplotlib's PyPlot:

plt.scatter(TMIN, PRCP)
plt.show()

The graph that we have produced is interpretable, but it is looking a little plain. Let's try customizing it. We want to customize the background of our plot using a couple of different methods.

Change Plot Background in Matplotlib

Now, let's go ahead and change the background of this plot. We can do this with two different approaches. We can change the color of the face, which is currently set to white. Or, we can input a picture using imshow().

Change Axes Background in Matplotlib

Let's first change the color of the face. This can either be done with the set() function, passing in the face argument and its new value, or via the dedicated set_facecolor() function:

ax = plt.axes()
ax.set_facecolor("orange")
# OR
ax.set(facecolor = "orange")

plt.scatter(TMIN, PRCP)
plt.show()

Either of these approaches produces the same result, as they both call on the same function under the hood.

Change Figure Background in Matplotlib

If you would like to set the background for the figure and need the axes to be transparent, this can be done with the set_alpha() argument when you create the figure. Let's create a figure and an axes object. Of course, you can also use the set() function, and pass the alpha attribute instead.

The color of the entire figure will be blue and we will initially set the alpha of the axes object to 1.0, meaning fully opaque. We color the axes object orange, giving us an orange background within the blue figure:

fig = plt.figure()
fig.patch.set_facecolor('blue')
fig.patch.set_alpha(0.6)

ax = fig.add_subplot(111)
ax.patch.set_facecolor('orange')
ax.patch.set_alpha(1.0)

plt.scatter(TMIN, PRCP)
plt.show()

Now let's see what happens when we adjust the alpha of the axes subplot down to 0.0:

fig = plt.figure()
fig.patch.set_facecolor('blue')
fig.patch.set_alpha(0.6)

ax = fig.add_subplot(111)
ax.patch.set_facecolor('orange')
ax.patch.set_alpha(0.0)

plt.scatter(TMIN, PRCP)
plt.show()

Notice that the background of the plot itself is transparent now.

Add Image to Plot Background in Matplotlib

If you would like to use an image as the background for a plot, this can be done by using PyPlot's imread() function. This function loads an image into Matplotlib, which can be displayed with the function imshow().

In order to plot on top of the image, the extent of the image has to be specified. By default, Matplotlib uses the upper left corner of the image as the image's origin. We can give a list of points to the imshow() function, specifying what region of the image should be displayed. When combined with subplots, another plot can be inserted on top of the image.

Let's use an image of rain as the background for our plot:

img = plt.imread("rain.jpg")
fig, ax = plt.subplots()
ax.imshow(img, extent=[-5, 80, -5, 30])
ax.scatter(TMIN, PRCP, color="#ebb734")
plt.show()

The extent argument takes in additional arguments in this order: horizontal_min, horizontal_max, vertical_min, vertical_max).

Here, we've read the image, cropped it and showed it on the axes using imshow(). Then, we plotted the scatter plot with a different color and showed the plot.

Conclusion

In this tutorial, we've gone over several ways to change the background of a plot using Python and Matplotlib.

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