Open CV 学习笔记：访问图像中像素的几种方法

1.利用.ptr 和 []的方法

2.利用Mat_ iteractor迭代器

3.利用动态地址计算配合at 的方法

4.利用.ptr 和 * ++ 以及模操作的方法


5.利用操作符重载

#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>

using namespace std;
using namespace cv;

void colorReduce1(Mat& inputImage,Mat& outputImage,int div){
outputImage = inputImage.clone();

int rows = inputImage.rows;
int cols = inputImage.cols*inputImage.channels();

for(int i = 0;i < rows;i++){
uchar *data = outputImage.ptr<uchar>(i);
for(int j = 0;j < cols;j++){
data[j] = data[j]/div*div + div/2;
}
}
}

void colorReduce2(Mat &inputImage,Mat &outputImage,int div){
outputImage = inputImage.clone();

Mat_<Vec3b>::iterator it = outputImage.begin<Vec3b>();
Mat_<Vec3b>::iterator itend = outputImage.end<Vec3b>();

for(;it != itend;it++){
(*it)[0] = (*it)[0]/div*div + div/2;
(*it)[1] = (*it)[1]/div*div + div/2;
(*it)[2] = (*it)[2]/div*div + div/2;

}
}
void colorReduce3(Mat &inputImage,Mat &outputImage,int div){
outputImage = inputImage.clone();
int rows = inputImage.rows;
int cols = inputImage.cols;

for(int i = 0;i < rows;i++){
for(int j = 0;j < cols;j++){
outputImage.at<Vec3b>(i,j)[0] = outputImage.at<Vec3b>(i,j)[0]/div*div + div/2;
outputImage.at<Vec3b>(i,j)[1] = outputImage.at<Vec3b>(i,j)[1]/div*div + div/2;
outputImage.at<Vec3b>(i,j)[2] = outputImage.at<Vec3b>(i,j)[2]/div*div + div/2;
}
}
}
void colorReduce4(Mat &inputImage,Mat &outputImage, int div) {

int nl= inputImage.rows;
int nc= inputImage.cols * inputImage.channels(); //每行元素的总元素数量
outputImage = inputImage.clone();
int n= static_cast<int>(log(static_cast<double>(div))/log(2.0));
//掩码值
uchar mask= 0xFF<<n;

for (int j=0; j<nl; j++) {

uchar* data= outputImage.ptr<uchar>(j);

for (int i=0; i<nc; i++) {

*data++= *data&mask + div/2;

}
}
}

void colorReduce5(Mat &inputImage,Mat &outputImage, int div){
outputImage = inputImage.clone();

int n= static_cast<int>(log(static_cast<double>(div))/log(2.0));
//掩码值
uchar mask= 0xFF<<n;

//进行色彩还原
outputImage=(outputImage&Scalar(mask,mask,mask))+Scalar(div/2,div/2,div/2);
}

int main(int argc,char **argv){
Mat img = imread("1.jpg");
imshow("原始图片",img);

Mat dst;
dst.create(img.size(),img.type());

//第1种方法
double time0 = static_cast<double>(getTickCount());

colorReduce1(img,dst,64);

time0 = ((double)getTickCount() - time0)/getTickFrequency();
cout<<"第1种方法的时间："<<time0<<endl;
imshow("处理后的图片1",dst);

//第2种方法
time0 = static_cast<double>(getTickCount());

colorReduce2(img,dst,64);

time0 = ((double)getTickCount() - time0)/getTickFrequency();
cout<<"第2种方法的时间："<<time0<<endl;
imshow("处理后的图片2",dst);

//第3种方法
time0 = static_cast<double>(getTickCount());

colorReduce3(img,dst,64);

time0 = ((double)getTickCount() - time0)/getTickFrequency();
cout<<"第3种方法的时间："<<time0<<endl;
imshow("处理后的图片3",dst);

//第4种方法
time0 = static_cast<double>(getTickCount());

colorReduce4(img,dst,64);

time0 = ((double)getTickCount() - time0)/getTickFrequency();
cout<<"第4种方法的时间："<<time0<<endl;

imshow("处理后的图片4",dst);

//第5种方法
time0 = static_cast<double>(getTickCount());

colorReduce5(img,dst,64);

time0 = ((double)getTickCount() - time0)/getTickFrequency();
cout<<"第5种方法的时间："<<time0<<endl;

imshow("处理后的图片5",dst);
waitKey(0);

return 0;
}

运行结果：