send an image (as numpy array) 'requests.post'

Question

I am bit puzzled with a very simple thing: I am using an online service for image processing and to send my image I'm using

var_0 = requests.post(api_url, params=params, headers=headers, data=image_data)

where image_data should be encode as a binary string. For example, the following example works properly:

image_data = open(image_path, "rb").read()
var_0 = requests.post(api_url, params=params, headers=headers, data=image_data)

However, in some cases I need to send an image while it is already opened and is in an numpy.array format.

How should I convert my image to be able to send through requests?

Answer 1

It is stated at the provided link "The supported input image formats includes JPEG, PNG, GIF(the first frame)s, BMP." Thus your data must be in one of those formats. A numpy array is not suitable. It needs to be converted to e.g. a PNG image.

This is most easily done using the matplotlib.pyplot.imsave() function. However, the result should be saved to a memory buffer (to be sent to the API), rather than to a file. The way to handle that in Python, is using an io.BytesIO() object.

Taken together, a solution to the problem is

import io
import numpy as np
import matplotlib.pyplot as plt

buf = io.BytesIO()
plt.imsave(buf, image_np, format='png')
image_data = buf.getvalue()
var_0 = requests.post(api_url, params=params, headers=headers, data=image_data)

where image_np is the image as a numpy array.

Note also that the line image_data = buf.getvalue() is not necessary. Instead the buffer contents can be used directly in the API call.