问Seaborn热图覆盖图像，但未显示任何内容

EN

import matplotlib.image as mpimg 
import matplotlib.cm
import seaborn as sns
import matplotlib.pyplot as plt

wd = matplotlib.cm.winter._segmentdata # only has r,g,b  
wd['alpha'] =  ((0.0, 0.0, 0.3), 
               (0.3, 0.3, 1.0),
               (1.0, 1.0, 1.0))

al_winter = matplotlib.colors.LinearSegmentedColormap('AlphaWinter', wd) 

map_img = mpimg.imread('./my_picture.png') 

hmax = sns.heatmap(results,
            cmap = al_winter, # this worked but I didn't like it
            #cmap = matplotlib.cm.winter,
            alpha = 0.5, # whole heatmap is translucent
            annot = True,
            zorder = 2
            )

# The heatmap is working as I can see the output in my notebook.

hmax.imshow(map_img,
          aspect = hmax.get_aspect(),
          extent = hmax.get_xlim() + hmax.get_ylim(),
          zorder = 1) #put the map under the heatmap
plt.show()

# Here the output is empty.