座標預設是從上到下，從左到右，例如
：

matplotlib.pyplot.imshow(X, cmap=None, norm=None, aspect=None, interpolation=None, alpha=None, 
                         vmin=None, vmax=None, origin=None, extent=None, shape=None, 
                         filternorm=1, filterrad=4.0, imlim=None, resample=None, 
                         url=
 
None, hold=None, data=None, **kwargs

他的引數很多，找了很久，才發現，應該是設定origin引數。

origin : [‘upper’ | ‘lower’], optional, default: None
    Place the [0,0] index of the array in the upper left or lower left corner of the axes. 
    If None, default to rc image.origin.

設origin=‘lower’，就得到如下圖：