Bug report

Bug summary

Hello, I am using plt.imshow to plot a very large array (~ 1 row x 150 million columns), and have noticed that the colors are not displayed properly.

Code for reproduction

import numpy as np
import matplotlib.pyplot as plt

# Very large
array = np.zeros(150000000, dtype=np.uint8)
array[len(array) // 2:] = 1
fig, ax = plt.subplots(figsize=(10, 3))
im = ax.imshow(array.reshape(1, -1), vmin=0, vmax=1, aspect='auto')
fig.colorbar(im, ax=ax)

# 10x smaller
array = np.zeros(15000000, dtype=np.uint8)
array[len(array) // 2:] = 1
fig, ax = plt.subplots(figsize=(10, 3))
im = ax.imshow(array.reshape(1, -1), vmin=0, vmax=1, aspect='auto')
fig.colorbar(im, ax=ax)

Actual outcome
Very large

10x smaller

Expected outcome
Since we set the later half of the array to 1 (and the rest is 0), we expect the image to change color at 75 million, but we see that all pixels are colored as 0.

Matplotlib version

• Operating system: Ubuntu 20.04
• Matplotlib version: 3.3.2 (also tested on 3.3.3)
• Matplotlib backend: module://ipykernel.pylab.backend_inline
• Python version: 3.8.3 (also tested on 3.6.9)
• Jupyter version (if applicable):
• Other libraries:

ipython                       7.18.1
ipython-genutils              0.2.0
jupyter                       1.0.0
jupyter-client                6.1.7
jupyter-console               6.2.0
jupyter-core                  4.6.3
jupyterlab                    2.2.8
jupyterlab-pygments           0.1.1
jupyterlab-server             1.2.0

Python installed via miniconda, but matplotlib was installed via pip.