Send and receive image data as JSON over the network with Python

Introduction

I wrote a code several times to send the image taken by the webcam to another server running the face detection model etc. via HTTP communication, so make a note so that you do not forget it. In the sample code, the image taken from the Web camera on the sending side is sent to the server at regular intervals, the face is detected on the receiving side, a box is drawn, and the image file is saved locally.

Sender

sender.py

import numpy as np
import cv2
import time
import json
import base64
import requests

def send_image(img):
  #Convert image to sendable format and store in JSON
  _, encimg = cv2.imencode(".png ", img)
  img_str = encimg.tostring()
  img_byte = base64.b64encode(img_str).decode("utf-8")
  img_json = json.dumps({'image': img_byte}).encode('utf-8')
  
  #Send HTTP request
  response = requests.post("http://localhost:8080/save", data=img_json)
  print('{0} {1}'.format(response.status_code, json.loads(response.text)["message"]))

if __name__ == '__main__':
  cap = cv2.VideoCapture(0)
  cap.set(cv2.CAP_PROP_FPS, 30)
  i = 0
  while True:
    _, img = cap.read()
    if i % 5 == 0:
      send_image(img)
    i += 1

Receiver

receiver.py

import os
import json
import cv2
import base64
import numpy as np
from datetime import datetime
from flask import Flask, request, Response
app = Flask(__name__)
count = 0

#Create a folder to save images
image_dir = "./images"
if not os.path.isdir(image_dir):
  os.mkdir(image_dir)

def detect_face(img):
  #Face detection model ('haarcascade_frontalface_default.xml') Can be downloaded from the link below
  # https://github.com/opencv/opencv/tree/master/data/haarcascades
  face_cascade = cv2.CascadeClassifier('haarcascade_frontalface_default.xml')
  faces = face_cascade.detectMultiScale(img, 1.3, 5)
  return faces

@app.route('/save', methods=['POST'])
def save_image():
    #Data conversion process
    data = request.data.decode('utf-8')
    data_json = json.loads(data)
    image = data_json['image']
    image_dec = base64.b64decode(image)
    data_np = np.fromstring(image_dec, dtype='uint8')
    decimg = cv2.imdecode(data_np, 1)

    #Detect face and draw box
    gray_img = cv2.cvtColor(decimg, cv2.COLOR_BGR2GRAY)
    faces = detect_face(gray_img)
    for (x,y,w,h) in faces:
      decimg = cv2.rectangle(decimg,(x,y),(x+w,y+h),(255,0,0),2)
    
    #Save image file
    global count
    filename = "./images/image{}.png ".format(count)
    cv2.imwrite(filename, decimg)
    count += 1

    #Send HTTP response
    return Response(response=json.dumps({"message": "{} was saved".format(filename)}), status=200)

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=8080)

reference

http://edosha.hatenablog.jp/entry/2017/09/05/174453 https://ysss.hateblo.jp/entry/2018/07/31/053507