gistfile1.txt

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

img = np.random.randn(300,300)*10**-6
myplot = plt.imshow(img)

def fmt(x, pos):
    a, b = '{:.2e}'.format(x).split('e')
    # x = a * 10**b = a * 10**(b-1) * 10**1
    a = float(a)
    b = int(b)
    return r'${:.10f} \times 10^{{{}}}$'.format(a * 10**(b-1), 1)

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