Bug summary

Pixel widths appear irregularly inpcolor(x, y, z, rasterized=True), whilex andy are regular. Usingrasterized=False provides correct (equal size) pixels, but saving the figure to.png (instead of.pdf) will show the same irregular pixel width bug.

It looks like a resampling bug, which messes up precise data visualization completely.

Code for reproduction

importnumpyasnpimportmatplotlib.pyplotaspltx,y=np.meshgrid(range(500),range(2))z= [np.tile([0,1],250),np.tile([0,1],250)]fig,ax=plt.subplots(1,1,figsize=(10,2))im=ax.pcolor(x,y,z,rasterized=True)ax.set_xticks(np.arange(0,40))fig.savefig('test.pdf')plt.show()

Actual outcome

In the resulting plot, some pixels are thinner, and some are thicker, than they should be.
rasterize=True (zoom-in to the lower left corner)

Expected outcome

rasterize=False (zoom-in to the lower left corner)

Additional information

• This behaviour depends on the number of pixels plotted, for me it becomes visible abovelen(x)>100.
• The spread between thicker and thinner lines increases with increasing size of the input array.
• If the view is reduced to a lower number of pixels (e.g.,ax.set_xlim(0,10)), the effect is no longer visible.

Operating system

Windows

Matplotlib Version

3.5.1

Matplotlib Backend

inline

Python version

3.9.6

Jupyter version

No response

Installation

pip