How to remove axis, legends, and white padding

I would like to apply colormap to an image, and write the resulting image, without using axes, labels, titles, or anything 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)?