this gist demonstrates the way to save a big numpy array as a binary string

dump_big_array.py

import json
import base64
import numpy as np
from io import BytesIO


# save data to the binary string
a = np.random.uniform(0, 255, (1500, 1500)).astype(np.uint8)
f = BytesIO()
np.savez_compressed(f, data=a)
f.seek(0)

# convert bytes to a string
code = base64.b64encode(f.read())  # type: bytes
string = code.decode('utf-8')  # type: str
f.close()

# dump the string to a json file
with open('test.json', 'w') as f:
    json.dump({"data": string}, f, indent=" "*4)

# load the string from a json file
with open('test.json', 'r') as f:
    data = json.load(f)["data"]
    
# convert sting to bytes
code = base64.b64decode(data)
f = BytesIO(code)
b = np.load(f, allow_pickle=True)['data']
f.close()
print(np.allclose(b, a))