Default dpi for savefig


I’m a little bit lost with respect to setting the resolution of images saved in png.
The matplotlibrc file sets the dpi to 80, but the default keyword argument of savefig is set to 150. Thus, changing the rc setting
to dpi=300 does not modify savefig’s default behaviour. Is there a way to set a default dpi that would be used when calling savefig ?