Scientific notation colorbar in matplotlib

Question

I am trying to put a colorbar to my image using matplotlib. The issue comes when I try to force the ticklabels to be written in scientific notation. How can I force the scientific notation (ie, 1x10^0, 2x10^0, ..., 1x10^2, and so on) in the ticks of the color bar?

Example, let's create and plot and image with its color bar:

import matplotlib as plot
import numpy as np

img = np.random.randn(300,300)
myplot = plt.imshow(img)
plt.colorbar(myplot)
plt.show()

When I do this, I get the following image:

However, I would like to see the ticklabels in scientific notation... Is there any one line command to do this? Otherwise, is there any hint out there? Thanks!

Answer 1

You could use colorbar 's format parameter :

import matplotlib.pyplot as plt
import numpy as np
import matplotlib.ticker as ticker

img = np.random.randn(300,300)
myplot = plt.imshow(img)

def fmt(x, pos):
    a, b = '{:.2e}'.format(x).split('e')
    b = int(b)
    return r'${} \times 10^{{{}}}$'.format(a, b)

plt.colorbar(myplot, format=ticker.FuncFormatter(fmt))
plt.show()

Answer 2

您可以指定颜色条刻度的格式，如下所示：

pl.colorbar(myplot, format='%.0e')

Answer 3

There is a more straightforward (but less customizable) way to get scientific notation in a ColorBar without the %.0e formatting.

Create your ColorBar :

cbar = plt.colorbar()

And call the formatter:

cbar.formatter.set_powerlimits((0, 0))

This will make the ColorBar use scientific notation. See the example figure below to see how the ColorBar will look.

The documentation for this function can be found here .

Answer 4

It seems that cbar.formatter.set_powerlimits((0,0)) alone in Joseph's answer does not render math format like $10^3$ yet.

Using further cbar.formatter.set_useMathText(True) gives something like $10^3$.

import matplotlib.pyplot as plt
import numpy as np

img = np.random.randn(300,300)*10**5
myplot = plt.imshow(img)
cbar = plt.colorbar(myplot)
cbar.formatter.set_powerlimits((0, 0))

# to get 10^3 instead of 1e3
cbar.formatter.set_useMathText(True)

plt.show()

generates plot .

See the document of set_useMathText() here .

PS: Maybe this suits best for a comment. But I do not have enough reputations.