Fix bad histogramming bins in mri/eeg example.

The previous version of the histogram showed regular "spikes" which are
entirely artefactual; they come from the fact that we were binning
(effectively) integer data with floating point bins that did not all
cover the same number of ints (even though they have the same floating
point width).  Using an explicit, integer binsize avoids this issue.

Author: anntzer

galleries/examples/specialty_plots/mri_with_eeg.py

@@ -13,7 +13,6 @@
 import matplotlib.cbook as cbook
 import matplotlib.cm as cm
 from matplotlib.collections import LineCollection
-from matplotlib.ticker import MultipleLocator
 
 fig = plt.figure("MRI_with_EEG")
 
@@ -28,15 +27,10 @@
 
 # Plot the histogram of MRI intensity
 ax1 = fig.add_subplot(2, 2, 2)
-im = np.ravel(im)
-im = im[np.nonzero(im)]  # Ignore the background
-im = im / (2**16 - 1)  # Normalize
-ax1.hist(im, bins=100)
-ax1.xaxis.set_major_locator(MultipleLocator(0.4))
+im = im[im.nonzero()]  # Ignore the background
+ax1.hist(im, bins=np.arange(0, 2**16+1, 512))
+ax1.set(xlabel='Intensity (a.u.)', ylabel='MRI density', yticks=[])
 ax1.minorticks_on()
-ax1.set_yticks([])
-ax1.set_xlabel('Intensity (a.u.)')
-ax1.set_ylabel('MRI density')
 
 # Load the EEG data
 n_samples, n_rows = 800, 4
@@ -72,6 +66,5 @@
 
 ax2.set_xlabel('Time (s)')
 
-
 plt.tight_layout()
 plt.show()