Arrays are not equal after converting numpy array to byte array and back to numpy array

Question

I want to send an image which was imported by opencv imread to another computer via socket. But the data received and the data sent are not equal.

I have converted the numpy array data which I got by imread and converted it to byte array in order to send it via the socket. And then i have converted the byte array which was received at the other end back to the numpy array. But I can't view the image from the received data.

This is the code snippet in the senders end

im = cv2.imread('view.jpg')
stringimage = np.array_str(im)
byteimage = str.encode(stringimage)
sock.sendto(byteimage,("127.0.0.1",5002))

This is the code snippet in the receivers end

byteimage,addr = sock.recvfrom(1024)
decoded = bytes.decode(byteimage)
backstring = np.array(decoded)
cv2.imshow('RealSense', backstring)
cv2.waitKey(0)

I got this error

TypeError: mat data type = 19 is not supported

for this line of code

cv2.imshow('RealSense', backstring)

Update

After getting the suggestions bellow and referring some other materials I have come up with a solution which is working for my scenario.

Image senders side

#color_image is my opencv image

retval, data = cv2.imencode('.jpg', color_image, ENCODE_PARAMS)
b64_bytes = base64.b64encode(data)
b64_string = b64_bytes.decode()
sock.sendto(str.encode(b64_string), ("127.0.0.1", 5002))

Image receivers side

data, addr = sock.recvfrom(60000)
img = imread(io.BytesIO(base64.b64decode(data)))

Please tell me if there is any bad coding in my solution

Katerina · Accepted Answer · 2019-11-08 06:48:07Z

2

A similar question was helpfully answered here.

The issue is that constructing the numpy array from a string doesn't parse the data as a float/int the way you wrote it (and converting to a string to send the data is unnecessary).

Here's a simplified example to apply that solution:

import numpy as np
from io import BytesIO

a = np.array([1, 2])
b = BytesIO()
np.save(b, a)

"""-----send the data-----"""
# send(b.getvalue())


data = BytesIO(b.getvalue())
c = np.load(data)
print(a)
print(c)

Resulting in:

[1 2]
[1 2]

answered Nov 8, 2019 at 6:48

Katerina

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2 Comments

Malith Prasanna Rathnasena Over a year ago

b.getvalue() can't be send through the socket. I tried sock.send(b.getvalue(),("127.0.0.1",5005)) . But I get this error "TypeError: an integer is required (got type tuple)"

Malith Prasanna Rathnasena Over a year ago

Thank you for the suggestion. I have come up with a solution. And updated it in the question. Thanks

Roy2511 · Accepted Answer · 2019-11-08 06:25:36Z

1

byteimage,addr = sock.recvfrom(1024)

This limits your buffer size to 1024 bytes.

Read docs

answered Nov 8, 2019 at 6:25

Roy2511

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3 Comments

Roy2511 Over a year ago

I suspect the np.array_str command is the root of the issue. But all this is unnecessary. It seems like you want to send the image from one socket to another. See this answer

Malith Prasanna Rathnasena Over a year ago

Thank you for note that point out. I have increased the buffer size to 256,000 bytes . But the issue remains same. My image size is 71,470 bytes

Malith Prasanna Rathnasena Over a year ago

I had to compress the image and increase the buffer size in order to send the image. Thank you for the suggestion.

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