[python] Matplotlib plots: removing axis, legends and white spaces

I'm new to Python and Matplotlib, I would like to simply apply colormap to an image and write the resulting image, without using axes, labels, titles or anything usually automatically added by matplotlib. Here is what I did:

def make_image(inputname,outputname):
    data = mpimg.imread(inputname)[:,:,0]
    fig = plt.imshow(data)
    fig.set_cmap('hot')
    fig.axes.get_xaxis().set_visible(False)
    fig.axes.get_yaxis().set_visible(False)
    plt.savefig(outputname)

It successfully removes the axis of the figure, but the figure saved presents a white padding and a frame around the actual image. How can I remove them (at least the white padding)? Thanks