我试着设置一个图像，一个水印，在matplotlib图形的中心。我希望图像的中心在图形的中心。问题似乎是图形大小和10”x 10”和960 x 960像素的dpi与保存的图像（像素大小为610 x 623）之间的差异。当我通过图形添加图像时。figimage在960/2，960/2，这是完成的图像偏心。我的代码和示例图像如下。
创建绘图：

f, ax = plt.subplots(1, figsize=(10,10))
f.set_facecolor((1,1,1))
ax.set_title('{} Reflection Integrated Intensity vs Max Intensity of {}'.format(refl, rcmap.sample_number), size=14)
f = add_logo(f, '/home/zeppelin_d/Desktop/company.com_logo.png',x_frac=0.5, y_frac=0.5, scale=0.5, alpha=0.15)
ax = sns.regplot(x='z', y='int_int', data=df, scatter_kws={'alpha':0.4})
ax.set_xlabel('{} Max Intensity'.format(refl), size=14)
ax.set_ylabel('{} Integrated Intensity'.format(refl, size=14))
ax.set_xlim([0,max(df['z']) * 1.05])
ax.set_ylim([0,max(df['int_int']) * 1.05])

添加图像：

def add_logo(f, path, x_frac=0.5, y_frac=0.5, scale=1, alpha=1):
    """
    Add an image to the figure (not the axes)
    f: a matplotlib figure instance.
    path: the string path to the image to add to the figure.
    x_frac: the fraction of the x dimension of the figure to set the offset to.
        Must be a float.
    y_frac: the fraction of the y dimension of the figure to set the offset to.
        Must be a float.
    scale: the float scale by which to multiply to the image pixel dimensions.
    alpha: the alpha to set the inserted image to
    Set the figure dpi to the same as screen dpi.
    Use this like:
    f = add_logo(f, 'mah_business_logo.png',x_frac=0.5, y_frac=0.5, scale=0.5, alpha=0.15)
    for setting a watermark. This should put the center of the image in the center of the
    figure at half it's original size.
    """
    assert type(x_frac) == float and type(y_frac) == float,  "x_frac and y_frac must be floats."
    im = Image.open(path)
    f.set_dpi(96)
    im.thumbnail((int(im.size[0] * scale), int(im.size[1] * scale)), Image.ANTIALIAS)
    img_x, img_y = im.size[0], im.size[1]
    x_offset = int((f.bbox.xmax * x_frac - img_x/2))
    y_offset = int((f.bbox.ymax * y_frac - img_y/2))
    f.figimage(im, xo=x_offset, yo=y_offset, origin='upper', zorder=10, alpha=alpha)
    return f

x1c 0d1x我怎样才能知道保存的图像在任何比例下的尺寸？或者为什么完成的图像实际上不是10 x10”和960 x960 pixels？谢谢。