Read image file pixel value and write it to a data frame, saved it to csv, when I reload, Image can't show

Question

First I open images and get their pixel value, then write to a dataframe.

skin_df_balanced['pix'] = skin_df_balanced['path'].map(lambda x: np.asarray(Image.open(x).resize((SIZE,SIZE)))) 

Then I saved this dataframe to csv:

skin_df_balanced.to_csv('./skin_df_balanced_pixel_value_500.csv')

But when I reload the csv and tried to plot the images:

test = pd.read_csv('./skin_df_balanced_pixel_value_500.csv',index_col=0)

n_samples = 5

fig, m_axs = plt.subplots(7, n_samples, figsize = (4*n_samples, 3*7))
for n_axs, (type_name, type_rows) in zip(m_axs, test.sort_values(['type']).groupby('type')):
    n_axs[0].set_title(type_name)
    for c_ax, (_, c_row) in zip(n_axs, type_rows.sample(n_samples, random_state=1234).iterrows()):
        c_ax.imshow(c_row['pix'])
        c_ax.axis('off')

I found this error:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-26-abe099827f62> in <module>()
      5     n_axs[0].set_title(type_name)
      6     for c_ax, (_, c_row) in zip(n_axs, type_rows.sample(n_samples, random_state=1234).iterrows()):
----> 7         c_ax.imshow(c_row['pix'])
      8         c_ax.axis('off')

4 frames
/usr/local/lib/python3.7/dist-packages/matplotlib/image.py in set_data(self, A)
    692                 not np.can_cast(self._A.dtype, float, "same_kind")):
    693             raise TypeError("Image data of dtype {} cannot be converted to "
--> 694                             "float".format(self._A.dtype))
    695 
    696         if not (self._A.ndim == 2

TypeError: Image data of dtype <U629 cannot be converted to float