Run Length Encoding (vertical) on an OpenCV uchar Mat

OpenCV_Vertical_RLE.cpp

#include <opencv2/opencv.hpp>
using namespace cv;

/**
 * Compute RLE.
 * RLE is encoded in a vector of vectors of (run length, value).
 * 
 * @param patch_    the 8UC1 image to work on
 * @param whichWay  by which dimension? rows = 0, columns != 0
 */
vector<vector<pair<int,int> > > CalculateRLE(const Mat& patch_, int whichWay = 0) {
    assert(!patch_.empty() && patch_.size().area() > 0 && patch_.type() == CV_8UC1);

    Mat patch = (whichWay != 0) ? patch_.t() : patch_;  // in case we want to RLE rows

    vector<vector<pair<int,int> > > RLE;

    //Adapted from: http://rosettacode.org/wiki/Run-length_encoding#Java
    for (int col = 0; col < patch.cols; ++col) {
       vector<pair<int,int> > colRLE;
       for (int it = 0; it < patch.rows; it++) {
           int runLength = 1;
           while (it+1 < patch.rows && patch.at<uchar>(it,col) == patch.at<uchar>(it+1,col)) {
               runLength++;
               it++;
           }
           colRLE.push_back(make_pair(runLength,(int)(patch.at<uchar>(it,col))));
       }
       RLE.push_back(colRLE);
    }

    return RLE;
}

//Simple usage example
int main() {
 Mat patch = imread("patch.png");
 if(patch.channels != 1) cvtColor(patch,patch,CV_BGR2GRAY);
 
 vector<vector<pair<int,int> > > RLE = CalculateRLE(patch > 0);
 
 //visualize the RLE and output to console
 Mat patch_RLE(patch.size(),CV_8UC3,Scalar::all(0));
 for (int rle_it = 0; rle_it < RLE.size(); ++rle_it) {
     cout << rle_it << ": ";
     int tmp_pos = 0;
     for (int j = 0; j < RLE[rle_it].size(); ++j) {
         cout << RLE[rle_it][j].first << " " << RLE[rle_it][j].second << ", ";
         line(patch_RLE,
                 Point(rle_it,tmp_pos),
                 Point(rle_it,tmp_pos+RLE[rle_it][j].first),
                 Scalar(255,0,RLE[rle_it][j].second),1);
         tmp_pos += RLE[rle_it][j].first;
     }
     cout << endl;
 }
 imshow("patch",patch);
 imshow("RLE",patch_RLE);
 waitKey();
}