OpenCV中遍历图像

• iterator

Mat& ScanImageAndReduceIterator(Mat& I, const uchar* const table){    // accept only char type matrices    CV_Assert(I.depth() == CV_8U);    const int channels = I.channels();    switch(channels)    {    case 1:        {            MatIterator_<uchar> it, end;            for( it = I.begin<uchar>(), end = I.end<uchar>(); it != end; ++it)                *it = table[*it];            break;        }    case 3:        {            MatIterator_<Vec3b> it, end;            for( it = I.begin<Vec3b>(), end = I.end<Vec3b>(); it != end; ++it)            {                (*it)[0] = table[(*it)[0]];                (*it)[1] = table[(*it)[1]];                (*it)[2] = table[(*it)[2]];            }        }    }    return I;}

LUT

Mat lookUpTable(1, 256, CV_8U);    uchar* p = lookUpTable.data;    for( int i = 0; i < 256; ++i)        p[i] = table[i];  LUT(I, lookUpTable, J);

完整程序

/* * main.cpp * *  Created on: Mar 5, 2017 *      Author: may */#include <opencv2/core.hpp>#include <opencv2/core/utility.hpp>#include "opencv2/imgcodecs.hpp"#include <opencv2/highgui.hpp>#include <iostream>#include <sstream>using namespace std;using namespace cv;static void help(){    cout        << "\n--------------------------------------------------------------------------" << endl        << "This program shows how to scan image objects in OpenCV (cv::Mat). As use case"        << " we take an input image and divide the native color palette (255) with the "  << endl        << "input. Shows C operator[] method, iterators and at function for on-the-fly item address calculation."<< endl        << "Usage:"                                                                       << endl        << "./how_to_scan_images <imageNameToUse> <divideWith> [G]"                       << endl        << "if you add a G parameter the image is processed in gray scale"                << endl        << "--------------------------------------------------------------------------"   << endl        << endl;}Mat& ScanImageAndReduceIterator(Mat& I, const uchar* table);int main(){    help();    Mat I, J;    I = imread("image.jpg");    if (I.empty())    {        cout << "The image could not be loaded." << endl;        return -1;    }    //! [dividewith]    int divideWith = 7; // convert our input string to number - C++ style    uchar table[256];    for (int i = 0; i < 256; ++i)       table[i] = (uchar)(divideWith * (i/divideWith));    //! [dividewith]    const int times = 100;    double t;    t = (double)getTickCount();    for (int i = 0; i < times; ++i)    {        cv::Mat clone_i = I.clone();        J = ScanImageAndReduceIterator(clone_i, table);    }    t = 1000*((double)getTickCount() - t)/getTickFrequency();    t /= times;    cout << "Time of reducing with the iterator (averaged for "        << times << " runs): " << t << " milliseconds."<< endl;    //! [table-init]    Mat lookUpTable(1, 256, CV_8U);    uchar* p = lookUpTable.ptr();    for( int i = 0; i < 256; ++i)        p[i] = table[i];    //! [table-init]    t = (double)getTickCount();    for (int i = 0; i < times; ++i)        //! [table-use]        LUT(I, lookUpTable, J);        //! [table-use]    t = 1000*((double)getTickCount() - t)/getTickFrequency();    t /= times;    cout << "Time of reducing with the LUT function (averaged for "        << times << " runs): " << t << " milliseconds."<< endl;    return 0;}//! [scan-iterator]Mat& ScanImageAndReduceIterator(Mat& I, const uchar* const table){    // accept only char type matrices    CV_Assert(I.depth() == CV_8U);    const int channels = I.channels();    switch(channels)    {    case 1:        {            MatIterator_<uchar> it, end;            for( it = I.begin<uchar>(), end = I.end<uchar>(); it != end; ++it)                *it = table[*it];            break;        }    case 3:        {            MatIterator_<Vec3b> it, end;            for( it = I.begin<Vec3b>(), end = I.end<Vec3b>(); it != end; ++it)            {                (*it)[0] = table[(*it)[0]];                (*it)[1] = table[(*it)[1]];                (*it)[2] = table[(*it)[2]];            }        }    }    return I;}//! [scan-iterator]

实验结果

最快的方法是LUT,因为利用了多线程。平时推荐Iterator方法，比较安全。