当两个人发送请求时，flask server 收到两个关于 OpenCV 的错误

Question

当两个人在我制作的烧瓶服务器上发送请求时，它是面罩检测，我在两个请求的函数 cvtColor 中都收到 opencv 错误。 当只有一个人发送请求时，一切正常。 Web服务器的目的是用于POST请求，以图片为参数，并返回面部坐标和有面具的百分比和没有面具的百分比的响应。 代码：

from tensorflow.keras.applications.mobilenet_v2 import preprocess_input
from tensorflow.keras.preprocessing.image import img_to_array
from tensorflow.keras.models import load_model
import numpy as np
import time
import cv2
import os
from flask import Flask, render_template, Response, send_from_directory, request
from flask_cors import CORS, cross_origin
import base64

def detect_and_predict_mask(frame, faceNet, maskNet):

    (h, w) = frame.shape[:2]
    blob = cv2.dnn.blobFromImage(frame, 1.0, (224, 224),
        (104.0, 177.0, 123.0))

    faceNet.setInput(blob)
    detections = faceNet.forward()

    faces = []
    locs = []
    preds = []

    for i in range(0, detections.shape[2]):

        confidence = detections[0, 0, i, 2]

        if confidence > 0.5:
            box = detections[0, 0, i, 3:7] * np.array([w, h, w, h])
            (startX, startY, endX, endY) = box.astype("int")

            (startX, startY) = (max(0, startX), max(0, startY))
            (endX, endY) = (min(w - 1, endX), min(h - 1, endY))

            face = frame[startY:endY, startX:endX]
            face = cv2.cvtColor(face, cv2.COLOR_BGR2RGB)
            face = cv2.resize(face, (224, 224))
            face = img_to_array(face)
            face = preprocess_input(face)

            faces.append(face)
            locs.append((startX, startY, endX, endY))

    if len(faces) > 0:
        faces = np.array(faces, dtype="float32")
        preds = maskNet.predict(faces, batch_size=32)
    return (locs, preds)

prototxtPath = r"face_detector\deploy.prototxt"
weightsPath = r"face_detector\res10_300x300_ssd_iter_140000.caffemodel"
faceNet = cv2.dnn.readNet(prototxtPath, weightsPath)

maskNet = load_model("mask_detector.model")

pom_frame = None

fapp = Flask(__name__)
cors = CORS(fapp)
fapp.config['CORS_HEADERS'] = 'Content-Type'

@fapp.route('/take_pic',methods=["POST"])
@cross_origin()
def disp_pic():
    data = request.form['image']
    img_binary = base64.b64decode(data)
    img_jpg = np.frombuffer(img_binary, dtype=np.uint8)
    frame = cv2.imdecode(img_jpg, cv2.IMREAD_COLOR)

    (locs, preds) = detect_and_predict_mask(frame, faceNet, maskNet)
    res_str = '{\"locs\":['
    for x in locs :
        res_str = res_str + '['
        for y in x :
            res_str += str(y) + ','
        if res_str[-1:] == ',':
           res_str = res_str[:-1]
        res_str += '],'
    if res_str[-1:] == ',':
        res_str = res_str[:-1]
    res_str += '],\"preds\":['
    for x in preds :
        res_str += '['
        for y in x :
            res_str += str(y) + ','
        if res_str[-1:] == ',':
           res_str = res_str[:-1]
        res_str += '],'
    if res_str[-1:] == ',':
        res_str = res_str[:-1]
    res_str += ']}'
            
    return res_str

if __name__ == '__main__':
    fapp.run(host="0.0.0.0", port=5000)

错误信息：

127.0.0.1 - - [16/Oct/2021 22:31:59] "POST /take_pic HTTP/1.1" 500 -
[2021-10-16 22:31:59,536] ERROR in app: Exception on /take_pic [POST]
Traceback (most recent call last):
  File "C:\Users\lazar\virenv\lib\site-packages\flask\app.py", line 2070, in wsgi_app
    response = self.full_dispatch_request()
  File "C:\Users\lazar\virenv\lib\site-packages\flask\app.py", line 1515, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "C:\Users\lazar\virenv\lib\site-packages\flask_cors\extension.py", line 165, in wrapped_function
    return cors_after_request(app.make_response(f(*args, **kwargs)))
  File "C:\Users\lazar\virenv\lib\site-packages\flask\app.py", line 1513, in full_dispatch_request
    rv = self.dispatch_request()
  File "C:\Users\lazar\virenv\lib\site-packages\flask\app.py", line 1499, in dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**req.view_args)
  File "C:\Users\lazar\virenv\lib\site-packages\flask_cors\decorator.py", line 128, in wrapped_function
    resp = make_response(f(*args, **kwargs))
  File "C:\Users\lazar\Documents\Python\facemask.py", line 114, in disp_pic
    (locs, preds) = detect_and_predict_mask(frame, faceNet, maskNet)
  File "C:\Users\lazar\Documents\Python\facemask.py", line 52, in detect_and_predict_mask
    face = cv2.cvtColor(face, cv2.COLOR_BGR2RGB)
cv2.error: OpenCV(4.5.1) C:\Users\appveyor\AppData\Local\Temp\1\pip-req-build-wvn_it83\opencv\modules\imgproc\src\color.cpp:182: error: (-215:Assertion failed) !_src.empty() in function 'cv::cvtColor'

Answer 1

该错误表明图像为空（ !_src.empty() ）。 在调用cvtColor之前的行中

尝试打印face或在（ face = frame[startY:endY, startX:endX] ）之后使用imshow以确保图像已正确上传和处理。

否则，请逐行确保POST请求成功并且图像实际发送到服务器。