gistfile1.txt

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

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

class FixedOrderFormatter(mticker.ScalarFormatter):
    # http://stackoverflow.com/questions/3677368/#3679918 (Joe Kington)
    """Formats axis ticks using scientific notation with a constant order of
    magnitude"""

    def __init__(self, order_of_mag=0, useOffset=True, useMathText=False):
        self._order_of_mag = order_of_mag
        mticker.ScalarFormatter.__init__(self, useOffset=useOffset,
                                        useMathText=useMathText)

    def _set_orderOfMagnitude(self, range):
        """Over-riding this to avoid having orderOfMagnitude reset elsewhere"""
        self.orderOfMagnitude = self._order_of_mag


plt.colorbar(myplot, format=FixedOrderFormatter(1))
plt.show()