[C++][STL] 수행시간 증가 문제

vector<float> getDataFromMat(Mat org, float weight, float bias, bool noise)
{
	auto imageHeight = org.rows;
	auto imageWidth = org.cols;
	auto offset = imageHeight * imageWidth;
 
	Mat mat = Mat();
	Mat matSplit[3];
	auto features = vector<float>(offset * org.channels());
        mat = org;
	split(mat, matSplit);
 
	parallel_for(0, mat.channels(), [&](auto i)
	{
		matSplit[i].convertTo(matSplit[i], CV_32F);
		copy((float*)matSplit[i].datastart, (float*)matSplit[i].dataend, features.begin() + offset * i);
	});
	}
 
	return features;
}
 
int main () 
{
	vector<Mat> images;
	cv::Mat image;
	string imagepath;
 
	for (int i(1); i < 4000; i++)
	{
		imagepath = "D:\\dog\\dog" + to_string(i) + ".jpg";
		image = cv::imread(imagepath);
		images.push_back(image);
	}
 
	vector<tuple<string, int, int, vector<float>>> vec = vector<tuple<string, int, int, vector<float>>>(4000);
	vector<Mat> imgs = images;
 
	for (int k(0); k < 100; k++)
	{
		clock_t start = clock();
		parallel_for(0, 4000, [&](auto i)
		{
			resize(imgs[i], imgs[i], Size(224, 224));
			vector<float> image_array = getDataFromMat(images[i], 1, 0, false);
			vec[i] = tuple< string, int, int, vector<float>>( "", 0, 0, image_array);
		});
 
		double t = (clock() - start) / (double)CLOCKS_PER_SEC;
		cout << t << endl;
		imgs.clear();
		vec.clear();
		imgs = images;
	}
}