Plot a Seaborn heatmap over a background picture

Question

I have a following problem. I would like to plot my heatmap over an image. See my simplified code below:

import pandas as pd
import seaborn as sns
import matplotlib.pyplot as plt
from PIL import Image


df = pd.DataFrame(np.array([[1, 2, 1], [4, 5, 1], [7, 8, 2], [8, 2, 3]]),
                   columns=['a', 'b', 'c'])

#make the df heatmap friendly
df_cnt = df.reset_index().pivot(index='a', 
                                            columns='b', values='c')

#missing values 
df_cnt.fillna(0, inplace=True)

#load an image
my_image = Image.open("./image.png")

#plot a an image
plt.imshow(my_image, zorder = 0)
#Note: I can see the image correctly in my IDE

#plot a heatmap
h = sns.heatmap(df_cnt)

#Heatmap is displayed but it is not over the backroung image....

What is the problem here? Is it because the color for 0 values in my heatmap is black?

I tried to follow answer here, but it did not work to me: Plotting seaborn heatmap on top of a background picture

score 2 · Accepted Answer · answered Feb 17 '21 at 09:43

You can use mpl.image in the answer you are referring to to overlay the image. You need to make sure to specify the transparency of the heatmap.

import matplotlib.image as mpimg # add
h = sns.heatmap(df_cnt, alpha=0.1, zorder=2) # update
my_image = mpimg.imread("./image.png") # update
# update
h.imshow(my_image,
         aspect=h.get_aspect(),
         extent= h.get_xlim() + h.get_ylim(),
         zorder=1)

plt.show() # add

Plot a Seaborn heatmap over a background picture

1 Answers1