"Crop" layer: supportBackend(cv::dnn::DNN_BACKEND_INFERENCE_ENGINE) returns false

1

I checked implementation status of layer in dnn module.
So, I tried to use supportBackend method.

This time, I used OpenCV 4.5.3(enabled Intel Inference Engine).
So, I guess that supportBackend(cv::dnn::DNN_BACKEND_INFERENCE_ENGINE) returns true. But, supportBackend(cv::dnn::DNN_BACKEND_INFERENCE_ENGINE) returns false. I don’t know why.

Source code

#include <opencv2/dnn.hpp>
#include <iostream>

int main()
{
	cv::dnn::LayerParams params;
	cv::Ptr<cv::dnn::Layer> layer = cv::dnn::LayerFactory::createLayerInstance("Crop", params);
	std::cout << "[Crop Layer]" << std::endl;
	std::cout << "  DNN_BACKEND_OPENCV: " << layer->supportBackend(cv::dnn::DNN_BACKEND_OPENCV) << std::endl;
	std::cout << "  DNN_BACKEND_CUDA: " << layer->supportBackend(cv::dnn::DNN_BACKEND_CUDA) << std::endl;
	std::cout << "  DNN_BACKEND_INFERENCE_ENGINE: " << layer->supportBackend(cv::dnn::DNN_BACKEND_INFERENCE_ENGINE) << std::endl;
	return 0;
}

Result

[Crop Layer]
  DNN_BACKEND_OPENCV: 1
  DNN_BACKEND_CUDA: 1
  DNN_BACKEND_INFERENCE_ENGINE: 0