Crop useless part of image obtained from matplotlib

Python Help
1

I created a picture with matplotlib and I saved it as a png.
I would like an autocrop tool, to save rectangle only and not all white space around it.
image

I use the following parameters:
fig1,ax1 = plt.subplots(1,1)
plt.axis(‘equal’)
plt.axis(‘off’)
plt.savefig(“rectangle.png”,bbox_inches=‘tight’)

I tryed adding transparent option too but not work:
plt.savefig(“rectangle.png”,bbox_inches=‘tight’,transparent=False)

thank you very much