I am not familiar with Plotly.js, and when I want to use it to plot images, I expect to get a result similar to plt.contourf(X, Y, Z, 50, alpha=.75, cmap='jet') in Matplotlib. However, I couldn’t find where to manually set the number of contour levels. It seems like you can only set the maximum value?
I just realized that the contour size can be set. That solves the problem.