How to convert numpy array to string and vice versa

Question

The following code is trying to convert the image array to string, and then regenerate the image from string.

import numpy as np
import matplotlib.pyplot as plt

image = np.ones((28,28))
print("image: {}".format(image.shape))

string = "{}".format(image.tostring())
print("len: {}".format(len(string)))

string_to_image = np.fromstring(string)
print("string_to_image: {}".format(string_to_image.shape))

Here is the output:

image: (28, 28)
len: 22739

/tmp/ipykernel_2794/3542140279.py:7: DeprecationWarning: tostring() is deprecated. Use tobytes() instead.
  string = "{}".format(image.tostring())
/tmp/ipykernel_2794/3542140279.py:10: DeprecationWarning: The binary mode of fromstring is deprecated, as it behaves surprisingly on unicode inputs. Use frombuffer instead
  string_to_image = np.fromstring(string)

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
/tmp/ipykernel_2794/3542140279.py in <cell line: 10>()
      8 print("len: {}".format(len(string)))
      9 
---> 10 string_to_image = np.fromstring(string)
     11 print("string_to_image: {}".format(string_to_image.shape))

ValueError: string size must be a multiple of element size

How to fix the error?

Abhishek · Accepted Answer · 2022-08-10 12:01:53Z

1

Check Below code, need to use right datatype dtype=np.uint8

string_to_image = np.fromstring(string, dtype=np.uint8)

answered Aug 10, 2022 at 12:01

Abhishek

1,6252 gold badges15 silver badges16 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Marco Kurepa · Accepted Answer · 2022-08-10 11:49:19Z

1

Alright so the first problem is the DeprecationWarning. With Python 3.2 and onwards, .tostring() and .fromstring have been replaced with .tobytes() and .frombuffer(). They are functionally the same, so you don't lose anything from using them, however for .frombuffer() to work properly we need to make sure we pass a bytes-like object so I removed the "{}".format() part.

The next problem is the shape. When you convert a numpy array to a string (or bytes-like object) it loses it's shape, however we cans imply fix this but using the .reshape() method.

And that's it, the code with all the changes is below and it should work as intended:)

import numpy as np
import matplotlib.pyplot as plt

image = np.ones((28,28))
print("image: {}".format(image.shape))

string = image.tobytes()
print("len: {}".format(str(string)))

string_to_image = np.frombuffer(string, dtype=int).reshape((28,28))
print("string_to_image: {}".format(string_to_image.shape))

answered Aug 10, 2022 at 11:49

Marco Kurepa

3001 silver badge9 bronze badges

1 Comment

stackbiz Over a year ago

The string in your code is a type of "bytes", my question is for converting it to "string" and then get the image from "string", not from bytes.

Collectives™ on Stack Overflow

How to convert numpy array to string and vice versa

2 Answers 2

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related