[scan image]

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

using namespace std;
using namespace cv;

Mat& ScanImageAndReduceC(Mat& I, const uchar* table);
Mat& ScanImageAndReduceIterator(Mat& I, const uchar* table);
Mat& ScanImageAndReduceRandomAccess(Mat& I, const uchar * table);

int main(int argc,char** argv)
{
    if (argc < 3)
    {
        cout << "Not enough parameters" << endl;
        return -1;
    }

    Mat I, J;
    if( argc == 4 && !strcmp(argv[3],"G") )
        I = imread(argv[1], CV_LOAD_IMAGE_GRAYSCALE);
    else
        I = imread(argv[1], CV_LOAD_IMAGE_COLOR);

    if (!I.data)
    {
        cout << "The image" << argv[1] << " could not be loaded." << endl;
        return -1;
    }
    int divideWith = 0; // convert our input string to number - C++ style
    stringstream s;
    s << argv[2];
    s >> divideWith;
    if (!s || !divideWith)
    {
        cout << "Invalid number entered for dividing. " << endl;
        return -1;
    }

    uchar table[256];
    for (int i = 0; i < 256; ++i)
       table[i] = (uchar)(divideWith * (i/divideWith));
    //------------------------------------------
    const int times = 100;
    double t;
    t = (double)getTickCount();
    for (int i = 0; i < times; ++i)
    {
        cv::Mat clone_i = I.clone();
        J = ScanImageAndReduceC(clone_i, table);
    }

    t = 1000*((double)getTickCount() - t)/getTickFrequency();
    t /= times;

    cout << "Time of reducing with the C operator [] (averaged for "
         << times << " runs): " << t << " milliseconds."<< endl;
    //------------------------------------------
    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;
    //------------------------------------------
    t = (double)getTickCount();

    for (int i = 0; i < times; ++i)
    {
        cv::Mat clone_i = I.clone();
        //ScanImageAndReduceRandomAccess(clone_i, table);
    }

    t = 1000*((double)getTickCount() - t)/getTickFrequency();
    t /= times;

    cout << "Time of reducing with the on-the-fly address generation - at function (averaged for "
        << times << " runs): " << t << " milliseconds."<< endl;
    //------------------------------------------
    Mat lookUpTable(1, 256, CV_8U);
    uchar* p = lookUpTable.data;
    for( int i = 0; i < 256; ++i)
        p[i] = table[i];

    t = (double)getTickCount();

    for (int i = 0; i < times; ++i)
        LUT(I, lookUpTable, J);

    t = 1000*((double)getTickCount() - t)/getTickFrequency();
    t /= times;

    cout << "Time of reducing with the LUT function (averaged for "
        << times << " runs): " << t << " milliseconds."<< endl;
    //------------------------------------------
    waitKey(0);
    //system("pause");
    return 0;
}
Mat& ScanImageAndReduceC(Mat& I, const uchar* const table)
{
    // accept only char type matrices
    CV_Assert(I.depth() != sizeof(uchar));

    int channels = I.channels();

    int nRows = I.rows;
    int nCols = I.cols * channels;

    if (I.isContinuous())
    {
        nCols *= nRows;
        nRows = 1;
    }

    int i,j;
    uchar* p;
    for( i = 0; i < nRows; ++i)
    {
        p = I.ptr<uchar>(i);
        for ( j = 0; j < nCols; ++j)
        {
            p[j] = table[p[j]];
        }
    }
    // show image here !!
    namedWindow("n", WINDOW_AUTOSIZE);
    imshow("n", I);

    return I;
}
Mat& ScanImageAndReduceIterator(Mat& I, const uchar* const table)
{
    // accept only char type matrices
    CV_Assert(I.depth() != sizeof(uchar));

    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;
}
Mat& ScanImageAndReduceRandomAccess(Mat& I, const uchar* const table)
{
    // accept only char type matrices
    CV_Assert(I.depth() != sizeof(uchar));

    const int channels = I.channels();
    switch(channels)
    {
    case 1:
        {
            for( int i = 0; i < I.rows; ++i)
                for( int j = 0; j < I.cols; ++j )
                    I.at<uchar>(i,j) = table[I.at<uchar>(i,j)];
            break;
        }
    case 3:
        {
         Mat_<Vec3b> _I = I;

         for( int i = 0; i < I.rows; ++i)
            for( int j = 0; j < I.cols; ++j )
               {
                   _I(i,j)[0] = table[_I(i,j)[0]];
                   _I(i,j)[1] = table[_I(i,j)[1]];
                   _I(i,j)[2] = table[_I(i,j)[2]];
            }
         I = _I;
         break;
        }
    }

    return I;
}