name 'setPreferableBackend' is not defined

The error message "name 'setPreferableBackend' is not defined" typically occurs when the function or method setPreferableBackend() has not been imported or defined in the current scope.

setPreferableBackend() is a method of the OpenCV library that allows the programmer to select the preferred backend for running the computer vision algorithms. To use this method, you need to import the cv2 module and then call the method on an instance of the cv2.dnn_DNN class.

Here's an example of how to use setPreferableBackend() in Python:

import cv2

net = cv2.dnn_DNN.readNetFromCaffe('deploy.prototxt', 'model.caffemodel')

# set the preferred backend to OpenCV
net.setPreferableBackend(cv2.dnn.DNN_BACKEND_OPENCV)

# process the input image using the neural network
output = net.forward(image)

Make sure that you have installed the OpenCV library and imported the cv2 module before using setPreferableBackend(). If you're still getting the same error, check your spelling and make sure that you're calling the method on the correct object.