1.介绍
对于图像像素点的遍历,我们常用的方法是动态地址运输(dst.at<Vec3b>(i, j)[0]),用这种方法的原因是简单易懂,但它的效率又是怎么样,没做过对比的话,可能的确是不清楚。用过c++或者c语言的人,说起要比速度,第一时间想到的是要上指针(对于结合汇编语言或者其它什么就先搁一下吧),另外,在c++中,用迭代器也是很快,那么究竟这三种方法谁是王者呢?
2.代码
以下代码比较简单,主要是以反色操作作为示例来讲解
#include<opencv2/core/core.hpp>
#include<opencv2/highgui/highgui.hpp>
#include<iostream>
using namespace std;
using namespace cv;
/*用指针访问像素*/
void invertColorPtr(Mat& src, Mat& dst) {
dst = src.clone();
int rowNumber = dst.rows;
int colNumber = dst.cols * dst.channels();
for (int i = 0; i < rowNumber; ++i) {
uchar* data = dst.ptr<uchar>(i);
for (int j = 0; j < colNumber; ++j)
data[j] = 255 - data[j];
}
}
/*用迭代器操作像素*/
void invertColorIte(Mat& src, Mat& dst) {
dst = src.clone();
Mat_<Vec3b>::iterator it = dst.begin<Vec3b>();
Mat_<Vec3b>::iterator itend = dst.end<Vec3b>();
for (; it != itend; ++it) {
(*it)[0] = 255 - (*it)[0];
(*it)[1] = 255 - (*it)[1];
(*it)[2] = 255 - (*it)[2];
}
}
/*动态地址计算*/
void invertColorDyn(Mat& src, Mat& dst) {
dst = src.clone();
int rowNumber = dst.rows;
int colNumber = dst.cols;
for (int i = 0; i < rowNumber; ++i) {
for (int j = 0; j < colNumber; ++j) {
dst.at<Vec3b>(i, j)[0] = 255 - dst.at<Vec3b>(i, j)[0];
dst.at<Vec3b>(i, j)[1] = 255 - dst.at<Vec3b>(i, j)[1];
dst.at<Vec3b>(i, j)[2] = 255 - dst.at<Vec3b>(i, j)[2];
}
}
}
int main() {
Mat srcImage = imread("131.png");
imshow("原始图片", srcImage);
Mat dstImage;
dstImage.create(srcImage.rows, srcImage.cols, srcImage.type());
double time0 = static_cast<double>(getTickCount());
invertColorPtr(srcImage, dstImage);
time0 = ((double)getTickCount() - time0) / getTickFrequency();
cout << "用指针访问像素方法运行时间为:" << time0 << "秒" << endl;
time0 = static_cast<double>(getTickCount());
invertColorIte(srcImage, dstImage);
time0 = ((double)getTickCount() - time0) / getTickFrequency();
cout << "用迭代器操作像素方法运行时间为:" << time0 << "秒" << endl;
time0 = static_cast<double>(getTickCount());
invertColorDyn(srcImage, dstImage);
time0 = ((double)getTickCount() - time0) / getTickFrequency();
cout << "用动态地址计算方法运行时间为:" << time0 << "秒" << endl;
imshow("效果图", dstImage);
waitKey(0);
return 0;
}
在Debug的情况下:
在Release的情况下(其实编译器做了一些优化):