Adding a Background Image to a Plot

Adding a background image to a plot

Use the extent keyword of imshow. The order of the argument is [left, right, bottom, top]

import numpy as np
import matplotlib.pyplot as plt

np.random.seed(0)
x = np.random.uniform(0.0,10.0,15)
y = np.random.uniform(0.0,10.0,15)

datafile = 'lena.jpg'
img = plt.imread(datafile)
plt.scatter(x,y,zorder=1)
plt.imshow(img, zorder=0, extent=[0.5, 8.0, 1.0, 7.0])
plt.show()

• For cases where it's desired to have an image in a small area of the scatter plot, change the order of the plots (.imshow then .scatter) and change the extent values.

plt.imshow(img, zorder=0, extent=[3.0, 5.0, 3.0, 4.50])
plt.scatter(x, y, zorder=1)
plt.show()

Add image to background of plot with Seaborn & Matplotlib

• Use the extent parameter as shown in Change values on matplotlib imshow() graph axis, but you must also use aspect='auto' and set figsize = (12, 12) (or (6, 6), etc.).
  
  • See all parameters at matplotlib.pyplot.imshow
• sns.scatterplot from the OP is commented out because no data was provided.
• Tested in python 3.8, matplotlib 3.4.2, and seaborn 0.11.1

import matplotlib.pyplot as plt
import seaborn as sns
import numpy as np  # sample data

img = plt.imread('CVGA.png')
fig, ax = plt.subplots(figsize=(6, 6))
# sns.scatterplot(data=min_max_day, x=min_max_day['Glucose Value (mg/dL)']['amin'], y=min_max_day['Glucose Value (mg/dL)']['amax'], zorder=1)

sns.scatterplot(x=np.linspace(110, 41, 10), y=np.linspace(110, 401, 10), ax=ax)
plt.xlim(110, 40)
plt.ylim(110, 400)

ax.imshow(img, extent=[110, 40, 110, 400], aspect='auto')

Add a background image to matplotlib plot / gif

I don't have a lot of experience with this, but I was able to display the image I called beforehand with plt.imshow(). The demo.gif could not be uploaded due to file size limitations. Sorry, the image used in the sample is not good. Sorry.

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation as animation
from matplotlib.animation import PillowWriter
import time
import matplotlib.image as mpimg

rng = np.random.default_rng()
fig = plt.figure(figsize=[10, 9])

img = mpimg.imread('lena_thumbnail_center_square.jpg')

ims = []
for i in range(200):
    df = pd.DataFrame(rng.integers(0, 100, size=(100, 2)), columns=list('xy'))
    x = df["x"]
    y = df["y"]
    im = plt.plot(x, y, "b.")
    ims.append(im)
#     print(i)   

ani = animation.ArtistAnimation(fig, ims, interval=500, blit=True,
                                repeat_delay=1000)
plt.imshow(img)

writer = PillowWriter(fps=2)
ani.save("demo2.gif", writer=writer)

Altair: How to make scatter plot aligned with image background created by mark_image?

Yes, if you change the values of x and y in your image plot to something like y=-200 and x=200, the image should be more centered in the scatter plot.

You can also change the anchor point of the image using align and baseline:

import altair as alt
import pandas as pd

source = pd.DataFrame.from_records([
      {"x": 2, "y": 2, "img": "https://vega.github.io/vega-datasets/data/7zip.png"}
])

imgs = alt.Chart(source).mark_image(
    width=100,
    height=100
).encode(
    x='x',
    y='y',
    url='img'
)

imgs + imgs.mark_circle(size=200, color='red', opacity=1)

imgs = alt.Chart(source).mark_image(
    width=100,
    height=100,
    align='right',
    baseline='top'
).encode(
    x='x',
    y='y',
    url='img'
)

imgs + imgs.mark_circle(size=200, color='red', opacity=1)

After this, you would still need to change the dimensions of the chart so that it has the same size as the image. The default is width=400 and height=300. You can get the dimensions of your image in most image editing software or using the file <imagename> command (at least on linux). But even after getting these dimensions, you would have to do some manual adjustments due to axes taking up some of that space in the chart.

how to fit the plot over a background image in R and ggplot2

You can set width and height arguments in rasterGrob both equal to 1 "npc", which will force the image to fill the plot area. Then specify the height and width of the image when you save it to get the aspect ratio you desire. Theme and scale_y_reverse options can be used to control the appearance of the axes as demonstrated also below. note that we can also use the expand parameter to ensure that the axes do not extend further than the image or data.

g <- rasterGrob(img, width=unit(1,"npc"), height=unit(1,"npc"), interpolate = FALSE)

g_ct <- ggplot(data=df_ct) +
  annotation_custom(g, -Inf, Inf, -Inf, Inf) +
  geom_path(aes_string(x=df_ct$X1, y=df_ct$X0), color='red', size=1) +
  scale_y_reverse("", 
                  labels = c(min(df_ct$X0), rep("", length(seq(min(df_ct$X0), max(df_ct$X0), 5))-2),max(df_ct$X0)), 
                  breaks = seq(min(df_ct$X0), max(df_ct$X0), 5),
                  expand = c(0,0)) +
  theme(plot.margin = unit(c(5,5,5,5), "mm"),
        axis.line.x = element_blank(),
        axis.ticks.x = element_blank(),
        axis.text.x = element_blank(),
        axis.line.y = element_blank(),
        axis.ticks.y = element_line(size = 1),
        axis.ticks.length = unit(5,'mm')) +
  scale_x_continuous("")
g_ct

ggsave('test.png', height=5, width = 2, units = 'in')

Some data:

df_ct <- data.frame(X0 = 0:100)
df_ct$X1 = sin(df_ct$X0) +rnorm(101)

and a background image:

https://i.stack.imgur.com/aEG7I.jpg

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