python - How to turn numpy array image to bytes?

Question

I need to recognize image with Google Vision API. Among the examples, they use following construction:

with io.open('test.png', 'rb') as image_file:
    content = image_file.read()
image = vision.types.Image(content=content)

I need to do similar, but my image comes from:

content = cv2.imread()

Which returns numpy array, not bytes. I tried:

content = content.tobytes()

Which converts array to bytes, but returns different bytes apparently, since it gives different result.
So how to make my image array similar to one which I get by open() function

Answer 1

Waitting for answers