How to achieve such picture effect using python？

I'm drawing a heat distribution map using python. But I found that the pixels of other people’s pictures looked like the first, and mine looked like the second.

It seems that other people's pictures have a cross highlight, but mine does not. I don't know what kind of processing has been done.I sincerely request help !!!

I use plt.imshow() to display the data, but I don’t know what kind of processing is required?

The first one suggests they are using plt.pcolormesh() with shading="gouraud", rather than plt.imshow().