Flask OpenCV Send and Receive Images in Bytes

I want to send and receive images in bytes in my flask API. I also want to send some json alongside the image. How can I achieve this?

Below is my current solution that does not work

flask:

@app.route('/add_face', methods=['GET', 'POST'])
def add_face():
if request.method == 'POST':
# print(request.json)
nparr = np.fromstring(request.form['img'], np.uint8)
print(request.form['img'])
img = cv2.imdecode(nparr, cv2.IMREAD_COLOR)

cv2.imshow("frame", img)
cv2.waitKey(1)

return "list of names & faces"


client:

def save_encoding(img_file):
URL = "http://localhost:5000/add_face"
img = open(img_file, 'rb').read()

response = requests.post(URL, data="name":"obama", "img":str(img))
print(response.content)


produced error:

cv2.imshow("frame", img)
cv2.error: OpenCV(3.4.3) /io/opencv/modules/highgui/src/window.cpp:356: error: (-215:Assertion failed) size.width>0 && size.height>0 in function 'imshow'


2 Answers
2

The following has worked for me.
I don't have the client code but I have a curl request. That should do the trick,

SERVER

from flask import request
from PIL import Image
import io

@app.route("/add_face", methods=["POST"])
def predict():
image = request.files["image"]
image_bytes = Image.open(io.BytesIO(image.read()))


CLIENT SIDE

curl -X POST -F image=@PATH/TO/FILE 'http://localhost:5000/add_face'


It is easier to send images in base64 format, by doing that you get rid of problems about sending/receiving binary data since you just work with a string. Also it is more convenient in web stuff. Tested code below:
Server side:

from flask import Flask, render_template, request
import pandas as pd
import cv2
import numpy as np
import base64

app = Flask(__name__)



@app.route('/add_face', methods=['GET', 'POST'])
def add_face():
if request.method == 'POST':
# read encoded image
imageString = base64.b64decode(request.form['img'])

# convert binary data to numpy array
nparr = np.fromstring(imageString, np.uint8)

# let opencv decode image to correct format
img = cv2.imdecode(nparr, cv2.IMREAD_ANYCOLOR);
cv2.imshow("frame", img)
cv2.waitKey(0)

return "list of names & faces"
if __name__ == '__main__':
app.run(debug=True, port=5000)


Client side:

import requests
import base64

URL = "http://localhost:5000/add_face"

# first, encode our image with base64
with open("block.png", "rb") as imageFile:
img = base64.b64encode(imageFile.read())

response = requests.post(URL, data="name":"obama", "img":str(img))
print(response.content)


You can use COLOR instead of ANYCOLOR if you are sure about your input images.

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