OpenCV VideoCapture 和错误：（-215：断言失败）！函数‘cv::cvtColor’中的 _src.empty()

问题描述：

我目前使用的是 Windows 10 和 Python 3.7，我尝试运行此代码，以使网络摄像头能够用于数字识别

def get_img_contour_thresh(img):
   x, y, w, h = 0, 0, 300, 300
   gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
   blur = cv2.GaussianBlur(gray, (5, 5), 0)
   ret, thresh1 = cv2.threshold(blur, 175, 255, cv2.THRESH_BINARY_INV + 
     cv2.THRESH_OTSU)
   thresh1 = thresh1[y:y + h, x:x + w]
   contours, hierarchy = cv2.findContours(thresh1, cv2.RETR_TREE, 
     cv2.CHAIN_APPROX_SIMPLE)[-2:]
   return img, contours, thresh1

def show_webcam(mirror=False):
   # load json and create model
   json_file = open('model.json', 'r')
   loaded_model_json = json_file.read()
   json_file.close()
   model = model_from_json(loaded_model_json)
   # load weights into new model
   model.load_weights("model.h5")
   print("Loaded model from disk")

model.compile(loss='categorical_crossentropy',
              optimizer='adam',
              metrics=['accuracy'])

cap = cv2.VideoCapture(0)
while True:
    ret, img = cap.read()
    img, contours, thresh = get_img_contour_thresh(img)
    ans = ''


    if len(contours) > 0:
        contour = max(contours, key=cv2.contourArea)
        if cv2.contourArea(contour) > 500:
            x, y, w, h = cv2.boundingRect(contour)
            newImage = thresh[y:y + h, x:x + w]
            newImage = cv2.resize(newImage, (28, 28))
            newImage = np.array(newImage)
            newImage = newImage.astype('float32')
            newImage /= 255

            if K.image_data_format() == 'channels_first':
                newImage = newImage.reshape(1, 28, 28)
            else:
                newImage = newImage.reshape(28, 28, 1)
            newImage = np.expand_dims(newImage, axis=0)
            ans = model.predict(newImage).argmax()


    x, y, w, h = 0, 0, 300, 300
    cv2.rectangle(img, (x, y), (x + w, y + h), (0, 255, 0), 2)
    cv2.putText(img, "CNN : " + str(ans), (10, 320),
                cv2.FONT_HERSHEY_SIMPLEX, 0.7, (0, 0, 255), 2)
    cv2.imshow("Frame", img)
    cv2.imshow("Contours", thresh)     


    if cv2.waitKey(1) & 0xFF == ord('q'):
        break
cap.release()
cv2.destroyAllWindows()


def main():
   show_webcam(mirror=True)


if __name__ == '__main__':
   main()

我收到此错误

 File "cam.py", line 75, in <module>
   main()
 File "cam.py", line 71, in main
   show_webcam(mirror=True)
 File "cam.py", line 34, in show_webcam
   img, contours, thresh = get_img_contour_thresh(img)
 File "cam.py", line 10, in get_img_contour_thresh
   gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
 cv2.error: OpenCV(3.4.4) C:projectsopencv- 
   pythonopencvmodulesimgprocsrccolor.cpp:181: error: (-215:Assertion 
   failed) !_src.empty() in function 'cv::cvtColor'

我一直在寻找解决方案，但一直没能找到答案，我试着四处寻找，但就是想不通，你们觉得怎么样？感谢你们的帮助

解决方案 1：

您看到的错误是在None传递时发生的cv2.cvtColor。

后

ret, img = cap.read()

在继续操作之前检查一下是个好主意img is not None。根据您的输入源，cap.read()可能会失败。在我的一台笔记本电脑上，它至少会失败一次，然后才会开始返回有效的图像。