以二进制格式保存后，Python数组大小加倍

I have data stored in an array of size (4320,2160), reshaped from a list of length 4320*2160. When I save the file in binary format using numpy's tofile method, and then open the file I noticed that the array is double in length. How do I get the original values of the array? I'm assuming it has something to do with endianness, but i'm unfamiliar with dealing with it.I have data stored in an array of size (4320,21