Bug report

Bug summary

When interpolating a 2D heatmap on Windows, I get colored artifacts drawn over the 'bad' points. I am using LogNorm for normalization. I suspect it has something to do with the masked values caused by having 0s in a LogNorm. I set then to white with set_bad() function. On Linux, the interpolation looks entirely different (the white areas are not interpolated) and no artifacts can be seen.

I've also tried different interpolating methods, all of them seem to create artifacts, except for nearest.

Zooming in creates more artifacts:

Zooming in to one of these artifacts, reveals this:

Code for reproduction

import matplotlib.pyplot as plt
import matplotlib.colors

heatmap = [[0] * 32 for _ in range(128)]
cnt = 0
last = 1
for lvl in range(127):
    if lvl % 20 < 10:
        for i in range(32):
            heatmap[lvl][i] = 40
    else:
        for i in range(32):
            heatmap[lvl][i] = 0
jet = plt.get_cmap('jet')
jet.set_bad('white', 1)

plt.imshow(heatmap, origin='lower', interpolation='gaussian', aspect='auto', cmap=jet,
                 norm=matplotlib.colors.LogNorm())
plt.show()

Matplotlib version

• Operating system: Windows
• Matplotlib version: 2.1.0
• Matplotlib backend (print(matplotlib.get_backend())): TkAgg
• Python version: 3.6
• Jupyter version (if applicable):
• Other libraries: