小赵学习Opencv(3)之高效图像遍历循环

本文主要实现了图像的负片算法，具体实现过程中，分别采用了四种遍历图像像素的方式，并对其遍历时间进行了对比。

四种访问方式分别如下：

【方式一类数组方式】

void Negative1(Mat image, Mat &result)
{
	result.create(image.size(), image.type());
	result.setTo(0);

	int i, j;
	int nl = image.rows;//行数
	int nc = image.cols;//列数
	for (int j = 0; j < nl; j++)
	{
		for (int i = 0; i < nc; i++)
		{
			result.at<Vec3b>(j, i)[0] = 255 - image.at<Vec3b>(j, i)[0];
			result.at<Vec3b>(j, i)[1] = 255 - image.at<Vec3b>(j, i)[1];
			result.at<Vec3b>(j, i)[2] = 255 - image.at<Vec3b>(j, i)[2];
		}
	}
}

【方式二迭代器方式】

void Negative2(Mat image, Mat &result)
{
	result.create(image.size(), image.type());
	result.setTo(0);

	Mat_<Vec3b>::iterator it = image.begin<Vec3b>();
	Mat_<Vec3b>::iterator itend = image.end<Vec3b>();
	Mat_<Vec3b>::iterator itt = result.begin<Vec3b>();

	for (; it != itend; ++it, ++itt)
	{
		(*itt)[0] = 255 - (*it)[0];
		(*itt)[1] = 255 - (*it)[1];
		(*itt)[2] = 255 - (*it)[2];
	}	
}

【方式三指针方式】

void Negative3(Mat image, Mat &result)
{
	result.create(image.size(), image.type());
	result.setTo(0);

	int i;
	int n = image.cols*image.rows*image.channels();//列数
	uchar *src = image.ptr<uchar>(0);
	uchar *dest = result.ptr<uchar>(0);
	for (i = 0; i < n ; i++)
	{
		*dest = 255 - *src;
		dest++, src++;
	}
}

【方式四改进指针方式】

void Negative4(Mat image, Mat &result)
{
	result.create(image.size(), image.type());
	result.setTo(0);

	int i;
	int n = image.cols*image.rows;//列数
	uchar *src = image.ptr<uchar>(0);
	uchar *dest = result.ptr<uchar>(0);
	for (i = 0; i < n; i++)
	{
		*dest = 255 - *src;
		dest++, src++;
		*dest = 255 - *src;
		dest++, src++;
		*dest = 255 - *src;
		dest++, src++;
	}
}

【测试代码】

int main()
{
	Mat image = imread("1.jpg");
	if (image.empty())
	{
		cout << "read file error!" << endl;
		return -1;
	}
	Mat result1, result2, result3, result4;
	double duration;
	duration = static_cast<double>(getTickCount());
	Negative1( image,  result1);
	duration = static_cast<double>(getTickCount())-duration;
	duration /= getTickFrequency();
	cout << "time consume is " << duration << " ms."<<endl;

	duration = static_cast<double>(getTickCount());
	Negative2(image, result2);
	duration = static_cast<double>(getTickCount()) - duration;
	duration /= getTickFrequency();
	cout << "time consume is " << duration << " ms." << endl;

	duration = static_cast<double>(getTickCount());
	Negative3(image, result3);
	duration = static_cast<double>(getTickCount()) - duration;
	duration /= getTickFrequency();
	cout << "time consume is " << duration << " ms." << endl; 

	duration = static_cast<double>(getTickCount());
	Negative4(image, result4);
	duration = static_cast<double>(getTickCount()) - duration;
	duration /= getTickFrequency();
	cout << "time consume is " << duration << " ms." << endl;

	imshow("0", image);
	imshow("1", result1);
	imshow("2", result2);
	imshow("3", result3);
	imshow("4", result4); 

	waitKey(0);
	system("pause");
	return 0;
}

【运行时间效果对比】



由上图可知，通过指针方式遍历优于通过迭代器方式遍历，通过迭代器方式遍历优于通过数组器方式遍历。