matplotlib imshow fixed aspect and vertical colorbar matching master axis height

问题

I need to plot a mesh grid with "temperature map" values, currently I'm using imshow, with a colormap. This is described in the Matplotlib overview, so I modified the example to force custom aspect of the figure:

import matplotlib.pyplot as plt
from mpl_toolkits.axes_grid1 import make_axes_locatable
import numpy as np

plt.figure()
ax = plt.gca()
im = ax.imshow(np.arange(100).reshape((10,10)), aspect=0.5)

# create an axes on the right side of ax. The width of cax will be 5%
# of ax and the padding between cax and ax will be fixed at 0.05 inch.
divider = make_axes_locatable(ax)
cax = divider.append_axes("right", size="5%", pad=0.05)

plt.colorbar(im, cax=cax)

plt.savefig("test.png")

But the result is not what I want, the colorbar is higher than the master axis:

Interestingly, when the colormap is horizontal, it is scaled properly:

cax = divider.append_axes("bottom", size="5%", pad=0.05)
plt.colorbar(im, cax=cax, orientation="horizontal")

回答1:

What happens here is that you applied an aspect of 0.5 to the imshow image. This divides the vertical extend of your image by 2, while the colorbar keeps the original extent. I see 2 solutions

you can manually set the size of the colorbar using:

cax = fig.add_axes([0.85, 0.3, 0.04, 0.4])

...or you can apply an aspect to cax to keep its y-dimension consequent with the image. In your case as you set size to 5%, setting aspect=1 would give you an image with 1/20 of the original vertical-extent. To obtain 1/2 as for the image set aspect to 20*0.5= 10. You could create a variable for aspect, if you want to experiment with changing the aspect on the figure, the colorbar will follow.

import matplotlib.pyplot as plt
from mpl_toolkits.axes_grid1 import make_axes_locatable
import numpy as np

fig = plt.figure()
ax = plt.gca()
im = ax.imshow(np.arange(100).reshape((10,10)), aspect=0.5)

# create an axes on the right side of ax. The width of cax will be 5%
# of ax and the padding between cax and ax will be fixed at 0.05 inch.
divider = make_axes_locatable(ax)
cax = divider.append_axes("right", size="5%", pad=0.05, aspect=10)
#cax = fig.add_axes([0.85, 0.3, 0.04, 0.4])
plt.colorbar(im, cax=cax)

plt.show()

来源：https://stackoverflow.com/questions/26563858/matplotlib-imshow-fixed-aspect-and-vertical-colorbar-matching-master-axis-height

标签

python

matplotlib