modules/features2d/src/mser.cpp

/* [<][>][^][v][top][bottom][index][help] */
This source file includes following definitions.
setDelta
getDelta
setMinArea
getMinArea
setMaxArea
getMaxArea
setPass2Only
getPass2Only
getGray
getNext
setNext
getDir
setDir
isVisited
updateTree
checkAndCapture
init
growHistory
merge
preprocess1
preprocess2
pass
ChiSquaredDistance
initMSCRNode
preprocessMSER_8uC3
findMSCR
MSCRStableCheck
extractMSER_8uC3
detectRegions
detect
create
/* Redistribution and use in source and binary forms, with or
 * without modification, are permitted provided that the following
 * conditions are met:
 *      Redistributions of source code must retain the above
 *      copyright notice, this list of conditions and the following
 *      disclaimer.
 *      Redistributions in binary form must reproduce the above
 *      copyright notice, this list of conditions and the following
 *      disclaimer in the documentation and/or other materials
 *      provided with the distribution.
 *      The name of Contributor may not be used to endorse or
 *      promote products derived from this software without
 *      specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
 * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
 * OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
 * TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 * Copyright© 2009, Liu Liu All rights reserved.
 *
 * OpenCV functions for MSER extraction
 *
 * 1. there are two different implementation of MSER, one for gray image, one for color image
 * 2. the gray image algorithm is taken from: Linear Time Maximally Stable Extremal Regions;
 *    the paper claims to be faster than union-find method;
 *    it actually get 1.5~2m/s on my centrino L7200 1.2GHz laptop.
 * 3. the color image algorithm is taken from: Maximally Stable Colour Regions for Recognition and Match;
 *    it should be much slower than gray image method ( 3~4 times );
 *    the chi_table.h file is taken directly from paper's source code which is distributed under GPL.
 * 4. though the name is *contours*, the result actually is a list of point set.
 */

#include "precomp.hpp"
#include "opencv2/imgproc/imgproc_c.h"
#include <limits>

namespace cv
{

using std::vector;

class MSER_Impl : public MSER
{
public:
    struct Params
    {
        Params( int _delta=5, int _min_area=60, int _max_area=14400,
                   double _max_variation=0.25, double _min_diversity=.2,
                   int _max_evolution=200, double _area_threshold=1.01,
                   double _min_margin=0.003, int _edge_blur_size=5 )
        {
            delta = _delta;
            minArea = _min_area;
            maxArea = _max_area;
            maxVariation = _max_variation;
            minDiversity = _min_diversity;
            maxEvolution = _max_evolution;
            areaThreshold = _area_threshold;
            minMargin = _min_margin;
            edgeBlurSize = _edge_blur_size;
            pass2Only = false;
        }

        int delta;
        int minArea;
        int maxArea;
        double maxVariation;
        double minDiversity;
        bool pass2Only;

        int maxEvolution;
        double areaThreshold;
        double minMargin;
        int edgeBlurSize;
    };

    explicit MSER_Impl(const Params& _params) : params(_params) {}

    virtual ~MSER_Impl() {}

    void setDelta(int delta) { params.delta = delta; }
    int getDelta() const { return params.delta; }

    void setMinArea(int minArea) { params.minArea = minArea; }
    int getMinArea() const { return params.minArea; }

    void setMaxArea(int maxArea) { params.maxArea = maxArea; }
    int getMaxArea() const { return params.maxArea; }

    void setPass2Only(bool f) { params.pass2Only = f; }
    bool getPass2Only() const { return params.pass2Only; }

    enum { DIR_SHIFT = 29, NEXT_MASK = ((1<<DIR_SHIFT)-1)  };

    struct Pixel
    {
        Pixel() : val(0) {}
        Pixel(int _val) : val(_val) {}

        int getGray(const Pixel* ptr0, const uchar* imgptr0, int mask) const
        {
            return imgptr0[this - ptr0] ^ mask;
        }
        int getNext() const { return (val & NEXT_MASK); }
        void setNext(int next) { val = (val & ~NEXT_MASK) | next; }

        int getDir() const { return (int)((unsigned)val >> DIR_SHIFT); }
        void setDir(int dir) { val = (val & NEXT_MASK) | (dir << DIR_SHIFT); }
        bool isVisited() const { return (val & ~NEXT_MASK) != 0; }

        int val;
    };
    typedef int PPixel;

    struct WParams
    {
        Params p;
        vector<vector<Point> >* msers;
        vector<Rect>* bboxvec;
        Pixel* pix0;
        int step;
    };

    // the history of region grown
    struct CompHistory
    {
        CompHistory()
        {
            parent_ = child_ = next_ = 0;
            val = size = 0;
            var = -1.f;
            head = 0;
            checked = false;
        }
        void updateTree( WParams& wp, CompHistory** _h0, CompHistory** _h1, bool final )
        {
            if( var >= 0.f )
                return;
            int delta = wp.p.delta;

            CompHistory* h0_ = 0, *h1_ = 0;
            CompHistory* c = child_;
            if( size >= wp.p.minArea )
            {
                for( ; c != 0; c = c->next_ )
                {
                    if( c->var < 0.f )
                        c->updateTree(wp, c == child_ ? &h0_ : 0, c == child_ ? &h1_ : 0, final);
                    if( c->var < 0.f )
                        return;
                }
            }

            // find h0 and h1 such that:
            //    h0->val >= h->val - delta and (h0->parent == 0 or h0->parent->val < h->val - delta)
            //    h1->val <= h->val + delta and (h1->child == 0 or h1->child->val < h->val + delta)
            // then we will adjust h0 and h1 as h moves towards latest
            CompHistory* h0 = this, *h1 = h1_ && h1_->size > size ? h1_ : this;
            if( h0_ )
            {
                for( h0 = h0_; h0 != this && h0->val < val - delta; h0 = h0->parent_ )
                    ;
            }
            else
            {
                for( ; h0->child_ && h0->child_->val >= val - delta; h0 = h0->child_ )
                    ;
            }

            for( ; h1->parent_ && h1->parent_->val <= val + delta; h1 = h1->parent_ )
                ;

            if( _h0 ) *_h0 = h0;
            if( _h1 ) *_h1 = h1;

            // when we do not well-defined ER(h->val + delta), we stop
            // the process of computing variances unless we are at the final step
            if( !final && !h1->parent_ && h1->val < val + delta )
                return;

            var = (float)(h1->size - h0->size)/size;
            c = child_;
            for( ; c != 0; c = c->next_ )
                c->checkAndCapture(wp);
            if( final && !parent_ )
                checkAndCapture(wp);
        }

        void checkAndCapture( WParams& wp )
        {
            if( checked )
                return;
            checked = true;
            if( size < wp.p.minArea || size > wp.p.maxArea || var < 0.f || var > wp.p.maxVariation )
                return;
            if( child_ )
            {
                CompHistory* c = child_;
                for( ; c != 0; c = c->next_ )
                {
                    if( c->var >= 0.f && var > c->var )
                        return;
                }
            }
            if( parent_ && parent_->var >= 0.f && var >= parent_->var )
                return;
            int xmin = INT_MAX, ymin = INT_MAX, xmax = INT_MIN, ymax = INT_MIN, j = 0;
            wp.msers->push_back(vector<Point>());
            vector<Point>& region = wp.msers->back();
            region.resize(size);
            const Pixel* pix0 = wp.pix0;
            int step = wp.step;

            for( PPixel pix = head; j < size; j++, pix = pix0[pix].getNext() )
            {
                int y = pix/step;
                int x = pix - y*step;

                xmin = std::min(xmin, x);
                xmax = std::max(xmax, x);
                ymin = std::min(ymin, y);
                ymax = std::max(ymax, y);

                region[j] = Point(x, y);
            }

            wp.bboxvec->push_back(Rect(xmin, ymin, xmax - xmin + 1, ymax - ymin + 1));
        }

        CompHistory* child_;
        CompHistory* parent_;
        CompHistory* next_;
        int val;
        int size;
        float var;
        PPixel head;
        bool checked;
    };

    struct ConnectedComp
    {
        ConnectedComp()
        {
            init(0);
        }

        void init(int gray)
        {
            head = tail = 0;
            history = 0;
            size = 0;
            gray_level = gray;
        }

        // add history chunk to a connected component
        void growHistory( CompHistory*& hptr, WParams& wp, int new_gray_level, bool final, bool force=false )
        {
            bool update = final;
            if( new_gray_level < 0 )
                new_gray_level = gray_level;
            if( !history || (history->size != size && size > 0 &&
                (gray_level != history->val || force)))
            {
                CompHistory* h = hptr++;
                h->parent_ = 0;
                h->child_ = history;
                h->next_ = 0;
                if( history )
                    history->parent_ = h;
                h->val = gray_level;
                h->size = size;
                h->head = head;

                history = h;
                h->var = FLT_MAX;
                h->checked = true;
                if( h->size >= wp.p.minArea )
                {
                    h->var = -1.f;
                    h->checked = false;
                    update = true;
                }
            }
            gray_level = new_gray_level;
            if( update && history )
                history->updateTree(wp, 0, 0, final);
        }

        // merging two connected components
        void merge( ConnectedComp* comp1, ConnectedComp* comp2,
                    CompHistory*& hptr, WParams& wp )
        {
            comp1->growHistory( hptr, wp, -1, false );
            comp2->growHistory( hptr, wp, -1, false );

            if( comp1->size < comp2->size )
                std::swap(comp1, comp2);

            if( comp2->size == 0 )
            {
                gray_level = comp1->gray_level;
                head = comp1->head;
                tail = comp1->tail;
                size = comp1->size;
                history = comp1->history;
                return;
            }

            CompHistory* h1 = comp1->history;
            CompHistory* h2 = comp2->history;

            gray_level = std::max(comp1->gray_level, comp2->gray_level);
            history = comp1->history;
            wp.pix0[comp1->tail].setNext(comp2->head);

            head = comp1->head;
            tail = comp2->tail;
            size = comp1->size + comp2->size;
            bool keep_2nd = h2->size > wp.p.minArea;
            growHistory( hptr, wp, -1, false, keep_2nd );
            if( keep_2nd )
            {
                h1->next_ = h2;
                h2->parent_ = history;
            }
        }

        PPixel head;
        PPixel tail;
        CompHistory* history;
        int gray_level;
        int size;
    };

    void detectRegions( InputArray image,
                        std::vector<std::vector<Point> >& msers,
                        std::vector<Rect>& bboxes );
    void detect( InputArray _src, vector<KeyPoint>& keypoints, InputArray _mask );

    void preprocess1( const Mat& img, int* level_size )
    {
        memset(level_size, 0, 256*sizeof(level_size[0]));

        int i, j, cols = img.cols, rows = img.rows;
        int step = cols;
        pixbuf.resize(step*rows);
        heapbuf.resize(cols*rows + 256);
        histbuf.resize(cols*rows);
        Pixel borderpix;
        borderpix.setDir(5);

        for( j = 0; j < step; j++ )
        {
            pixbuf[j] = pixbuf[j + (rows-1)*step] = borderpix;
        }

        for( i = 1; i < rows-1; i++ )
        {
            const uchar* imgptr = img.ptr(i);
            Pixel* pptr = &pixbuf[i*step];
            pptr[0] = pptr[cols-1] = borderpix;
            for( j = 1; j < cols-1; j++ )
            {
                int val = imgptr[j];
                level_size[val]++;
                pptr[j].val = 0;
            }
        }
    }

    void preprocess2( const Mat& img, int* level_size )
    {
        int i;

        for( i = 0; i < 128; i++ )
            std::swap(level_size[i], level_size[255-i]);

        if( !params.pass2Only )
        {
            int j, cols = img.cols, rows = img.rows;
            int step = cols;
            for( i = 1; i < rows-1; i++ )
            {
                Pixel* pptr = &pixbuf[i*step + 1];
                for( j = 1; j < cols-1; j++ )
                {
                    pptr[j].val = 0;
                }
            }
        }
    }

    void pass( const Mat& img, vector<vector<Point> >& msers, vector<Rect>& bboxvec,
              Size size, const int* level_size, int mask )
    {
        CompHistory* histptr = &histbuf[0];
        int step = size.width;
        Pixel *ptr0 = &pixbuf[0], *ptr = &ptr0[step+1];
        const uchar* imgptr0 = img.ptr();
        Pixel** heap[256];
        ConnectedComp comp[257];
        ConnectedComp* comptr = &comp[0];
        WParams wp;
        wp.p = params;
        wp.msers = &msers;
        wp.bboxvec = &bboxvec;
        wp.pix0 = ptr0;
        wp.step = step;

        heap[0] = &heapbuf[0];
        heap[0][0] = 0;

        for( int i = 1; i < 256; i++ )
        {
            heap[i] = heap[i-1] + level_size[i-1] + 1;
            heap[i][0] = 0;
        }

        comptr->gray_level = 256;
        comptr++;
        comptr->gray_level = ptr->getGray(ptr0, imgptr0, mask);
        ptr->setDir(1);
        int dir[] = { 0, 1, step, -1, -step };
        for( ;; )
        {
            int curr_gray = ptr->getGray(ptr0, imgptr0, mask);
            int nbr_idx = ptr->getDir();
            // take tour of all the 4 directions
            for( ; nbr_idx <= 4; nbr_idx++ )
            {
                // get the neighbor
                Pixel* ptr_nbr = ptr + dir[nbr_idx];
                if( !ptr_nbr->isVisited() )
                {
                    // set dir=1, next=0
                    ptr_nbr->val = 1 << DIR_SHIFT;
                    int nbr_gray = ptr_nbr->getGray(ptr0, imgptr0, mask);
                    if( nbr_gray < curr_gray )
                    {
                        // when the value of neighbor smaller than current
                        // push current to boundary heap and make the neighbor to be the current one
                        // create an empty comp
                        *(++heap[curr_gray]) = ptr;
                        ptr->val = (nbr_idx+1) << DIR_SHIFT;
                        ptr = ptr_nbr;
                        comptr++;
                        comptr->init(nbr_gray);
                        curr_gray = nbr_gray;
                        nbr_idx = 0;
                        continue;
                    }
                    // otherwise, push the neighbor to boundary heap
                    *(++heap[nbr_gray]) = ptr_nbr;
                }
            }

            // set dir = nbr_idx, next = 0
            ptr->val = nbr_idx << DIR_SHIFT;
            int ptrofs = (int)(ptr - ptr0);
            CV_Assert(ptrofs != 0);

            // add a pixel to the pixel list
            if( comptr->tail )
                ptr0[comptr->tail].setNext(ptrofs);
            else
                comptr->head = ptrofs;
            comptr->tail = ptrofs;
            comptr->size++;
            // get the next pixel from boundary heap
            if( *heap[curr_gray] )
            {
                ptr = *heap[curr_gray];
                heap[curr_gray]--;
            }
            else
            {
                for( curr_gray++; curr_gray < 256; curr_gray++ )
                {
                    if( *heap[curr_gray] )
                        break;
                }
                if( curr_gray >= 256 )
                    break;

                ptr = *heap[curr_gray];
                heap[curr_gray]--;

                if( curr_gray < comptr[-1].gray_level )
                    comptr->growHistory(histptr, wp, curr_gray, false);
                else
                {
                    // keep merging top two comp in stack until the gray level >= pixel_val
                    for(;;)
                    {
                        comptr--;
                        comptr->merge(comptr, comptr+1, histptr, wp);
                        if( curr_gray <= comptr[0].gray_level )
                            break;
                        if( curr_gray < comptr[-1].gray_level )
                        {
                            comptr->growHistory(histptr, wp, curr_gray, false);
                            break;
                        }
                    }
                }
            }
        }

        for( ; comptr->gray_level != 256; comptr-- )
        {
            comptr->growHistory(histptr, wp, 256, true, true);
        }
    }

    Mat tempsrc;
    vector<Pixel> pixbuf;
    vector<Pixel*> heapbuf;
    vector<CompHistory> histbuf;

    Params params;
};

/*

TODO:
the color MSER has not been completely refactored yet. We leave it mostly as-is,
with just enough changes to convert C structures to C++ ones and
add support for color images into MSER_Impl::detectAndLabel.
*/

const int TABLE_SIZE = 400;

static const float chitab3[]=
{
    0.f,  0.0150057f,  0.0239478f,  0.0315227f,
    0.0383427f,  0.0446605f,  0.0506115f,  0.0562786f,
    0.0617174f,  0.0669672f,  0.0720573f,  0.0770099f,
    0.081843f,  0.0865705f,  0.0912043f,  0.0957541f,
    0.100228f,  0.104633f,  0.108976f,  0.113261f,
    0.117493f,  0.121676f,  0.125814f,  0.12991f,
    0.133967f,  0.137987f,  0.141974f,  0.145929f,
    0.149853f,  0.15375f,  0.15762f,  0.161466f,
    0.165287f,  0.169087f,  0.172866f,  0.176625f,
    0.180365f,  0.184088f,  0.187794f,  0.191483f,
    0.195158f,  0.198819f,  0.202466f,  0.2061f,
    0.209722f,  0.213332f,  0.216932f,  0.220521f,
    0.2241f,  0.22767f,  0.231231f,  0.234783f,
    0.238328f,  0.241865f,  0.245395f,  0.248918f,
    0.252435f,  0.255947f,  0.259452f,  0.262952f,
    0.266448f,  0.269939f,  0.273425f,  0.276908f,
    0.280386f,  0.283862f,  0.287334f,  0.290803f,
    0.29427f,  0.297734f,  0.301197f,  0.304657f,
    0.308115f,  0.311573f,  0.315028f,  0.318483f,
    0.321937f,  0.32539f,  0.328843f,  0.332296f,
    0.335749f,  0.339201f,  0.342654f,  0.346108f,
    0.349562f,  0.353017f,  0.356473f,  0.35993f,
    0.363389f,  0.366849f,  0.37031f,  0.373774f,
    0.377239f,  0.380706f,  0.384176f,  0.387648f,
    0.391123f,  0.3946f,  0.39808f,  0.401563f,
    0.405049f,  0.408539f,  0.412032f,  0.415528f,
    0.419028f,  0.422531f,  0.426039f,  0.429551f,
    0.433066f,  0.436586f,  0.440111f,  0.44364f,
    0.447173f,  0.450712f,  0.454255f,  0.457803f,
    0.461356f,  0.464915f,  0.468479f,  0.472049f,
    0.475624f,  0.479205f,  0.482792f,  0.486384f,
    0.489983f,  0.493588f,  0.4972f,  0.500818f,
    0.504442f,  0.508073f,  0.511711f,  0.515356f,
    0.519008f,  0.522667f,  0.526334f,  0.530008f,
    0.533689f,  0.537378f,  0.541075f,  0.54478f,
    0.548492f,  0.552213f,  0.555942f,  0.55968f,
    0.563425f,  0.56718f,  0.570943f,  0.574715f,
    0.578497f,  0.582287f,  0.586086f,  0.589895f,
    0.593713f,  0.597541f,  0.601379f,  0.605227f,
    0.609084f,  0.612952f,  0.61683f,  0.620718f,
    0.624617f,  0.628526f,  0.632447f,  0.636378f,
    0.64032f,  0.644274f,  0.648239f,  0.652215f,
    0.656203f,  0.660203f,  0.664215f,  0.668238f,
    0.672274f,  0.676323f,  0.680384f,  0.684457f,
    0.688543f,  0.692643f,  0.696755f,  0.700881f,
    0.70502f,  0.709172f,  0.713339f,  0.717519f,
    0.721714f,  0.725922f,  0.730145f,  0.734383f,
    0.738636f,  0.742903f,  0.747185f,  0.751483f,
    0.755796f,  0.760125f,  0.76447f,  0.768831f,
    0.773208f,  0.777601f,  0.782011f,  0.786438f,
    0.790882f,  0.795343f,  0.799821f,  0.804318f,
    0.808831f,  0.813363f,  0.817913f,  0.822482f,
    0.827069f,  0.831676f,  0.836301f,  0.840946f,
    0.84561f,  0.850295f,  0.854999f,  0.859724f,
    0.864469f,  0.869235f,  0.874022f,  0.878831f,
    0.883661f,  0.888513f,  0.893387f,  0.898284f,
    0.903204f,  0.908146f,  0.913112f,  0.918101f,
    0.923114f,  0.928152f,  0.933214f,  0.938301f,
    0.943413f,  0.94855f,  0.953713f,  0.958903f,
    0.964119f,  0.969361f,  0.974631f,  0.979929f,
    0.985254f,  0.990608f,  0.99599f,  1.0014f,
    1.00684f,  1.01231f,  1.01781f,  1.02335f,
    1.02891f,  1.0345f,  1.04013f,  1.04579f,
    1.05148f,  1.05721f,  1.06296f,  1.06876f,
    1.07459f,  1.08045f,  1.08635f,  1.09228f,
    1.09826f,  1.10427f,  1.11032f,  1.1164f,
    1.12253f,  1.1287f,  1.1349f,  1.14115f,
    1.14744f,  1.15377f,  1.16015f,  1.16656f,
    1.17303f,  1.17954f,  1.18609f,  1.19269f,
    1.19934f,  1.20603f,  1.21278f,  1.21958f,
    1.22642f,  1.23332f,  1.24027f,  1.24727f,
    1.25433f,  1.26144f,  1.26861f,  1.27584f,
    1.28312f,  1.29047f,  1.29787f,  1.30534f,
    1.31287f,  1.32046f,  1.32812f,  1.33585f,
    1.34364f,  1.3515f,  1.35943f,  1.36744f,
    1.37551f,  1.38367f,  1.39189f,  1.4002f,
    1.40859f,  1.41705f,  1.42561f,  1.43424f,
    1.44296f,  1.45177f,  1.46068f,  1.46967f,
    1.47876f,  1.48795f,  1.49723f,  1.50662f,
    1.51611f,  1.52571f,  1.53541f,  1.54523f,
    1.55517f,  1.56522f,  1.57539f,  1.58568f,
    1.59611f,  1.60666f,  1.61735f,  1.62817f,
    1.63914f,  1.65025f,  1.66152f,  1.67293f,
    1.68451f,  1.69625f,  1.70815f,  1.72023f,
    1.73249f,  1.74494f,  1.75757f,  1.77041f,
    1.78344f,  1.79669f,  1.81016f,  1.82385f,
    1.83777f,  1.85194f,  1.86635f,  1.88103f,
    1.89598f,  1.91121f,  1.92674f,  1.94257f,
    1.95871f,  1.97519f,  1.99201f,  2.0092f,
    2.02676f,  2.04471f,  2.06309f,  2.08189f,
    2.10115f,  2.12089f,  2.14114f,  2.16192f,
    2.18326f,  2.2052f,  2.22777f,  2.25101f,
    2.27496f,  2.29966f,  2.32518f,  2.35156f,
    2.37886f,  2.40717f,  2.43655f,  2.46709f,
    2.49889f,  2.53206f,  2.56673f,  2.60305f,
    2.64117f,  2.6813f,  2.72367f,  2.76854f,
    2.81623f,  2.86714f,  2.92173f,  2.98059f,
    3.04446f,  3.1143f,  3.19135f,  3.27731f,
    3.37455f,  3.48653f,  3.61862f,  3.77982f,
    3.98692f,  4.2776f,  4.77167f,  133.333f
};

struct MSCRNode;

struct TempMSCR
{
    MSCRNode* head;
    MSCRNode* tail;
    double m; // the margin used to prune area later
    int size;
};

struct MSCRNode
{
    MSCRNode* shortcut;
    // to make the finding of root less painful
    MSCRNode* prev;
    MSCRNode* next;
    // a point double-linked list
    TempMSCR* tmsr;
    // the temporary msr (set to NULL at every re-initialise)
    TempMSCR* gmsr;
    // the global msr (once set, never to NULL)
    int index;
    // the index of the node, at this point, it should be x at the first 16-bits, and y at the last 16-bits.
    int rank;
    int reinit;
    int size, sizei;
    double dt, di;
    double s;
};

struct MSCREdge
{
    double chi;
    MSCRNode* left;
    MSCRNode* right;
};

static double ChiSquaredDistance( const uchar* x, const uchar* y )
{
    return (double)((x[0]-y[0])*(x[0]-y[0]))/(double)(x[0]+y[0]+1e-10)+
    (double)((x[1]-y[1])*(x[1]-y[1]))/(double)(x[1]+y[1]+1e-10)+
    (double)((x[2]-y[2])*(x[2]-y[2]))/(double)(x[2]+y[2]+1e-10);
}

static void initMSCRNode( MSCRNode* node )
{
    node->gmsr = node->tmsr = NULL;
    node->reinit = 0xffff;
    node->rank = 0;
    node->sizei = node->size = 1;
    node->prev = node->next = node->shortcut = node;
}

// the preprocess to get the edge list with proper gaussian blur
static int preprocessMSER_8uC3( MSCRNode* node,
                               MSCREdge* edge,
                               double* total,
                               const Mat& src,
                               Mat& dx,
                               Mat& dy,
                               int Ne,
                               int edgeBlurSize )
{
    int srccpt = (int)(src.step-src.cols*3);
    const uchar* srcptr = src.ptr();
    const uchar* lastptr = srcptr+3;
    double* dxptr = dx.ptr<double>();
    for ( int i = 0; i < src.rows; i++ )
    {
        for ( int j = 0; j < src.cols-1; j++ )
        {
            *dxptr = ChiSquaredDistance( srcptr, lastptr );
            dxptr++;
            srcptr += 3;
            lastptr += 3;
        }
        srcptr += srccpt+3;
        lastptr += srccpt+3;
    }
    srcptr = src.ptr();
    lastptr = srcptr+src.step;
    double* dyptr = dy.ptr<double>();
    for ( int i = 0; i < src.rows-1; i++ )
    {
        for ( int j = 0; j < src.cols; j++ )
        {
            *dyptr = ChiSquaredDistance( srcptr, lastptr );
            dyptr++;
            srcptr += 3;
            lastptr += 3;
        }
        srcptr += srccpt;
        lastptr += srccpt;
    }
    // get dx and dy and blur it
    if ( edgeBlurSize >= 1 )
    {
        GaussianBlur( dx, dx, Size(edgeBlurSize, edgeBlurSize), 0 );
        GaussianBlur( dy, dy, Size(edgeBlurSize, edgeBlurSize), 0 );
    }
    dxptr = dx.ptr<double>();
    dyptr = dy.ptr<double>();
    // assian dx, dy to proper edge list and initialize mscr node
    // the nasty code here intended to avoid extra loops
    MSCRNode* nodeptr = node;
    initMSCRNode( nodeptr );
    nodeptr->index = 0;
    *total += edge->chi = *dxptr;
    dxptr++;
    edge->left = nodeptr;
    edge->right = nodeptr+1;
    edge++;
    nodeptr++;
    for ( int i = 1; i < src.cols-1; i++ )
    {
        initMSCRNode( nodeptr );
        nodeptr->index = i;
        *total += edge->chi = *dxptr;
        dxptr++;
        edge->left = nodeptr;
        edge->right = nodeptr+1;
        edge++;
        nodeptr++;
    }
    initMSCRNode( nodeptr );
    nodeptr->index = src.cols-1;
    nodeptr++;
    for ( int i = 1; i < src.rows-1; i++ )
    {
        initMSCRNode( nodeptr );
        nodeptr->index = i<<16;
        *total += edge->chi = *dyptr;
        dyptr++;
        edge->left = nodeptr-src.cols;
        edge->right = nodeptr;
        edge++;
        *total += edge->chi = *dxptr;
        dxptr++;
        edge->left = nodeptr;
        edge->right = nodeptr+1;
        edge++;
        nodeptr++;
        for ( int j = 1; j < src.cols-1; j++ )
        {
            initMSCRNode( nodeptr );
            nodeptr->index = (i<<16)|j;
            *total += edge->chi = *dyptr;
            dyptr++;
            edge->left = nodeptr-src.cols;
            edge->right = nodeptr;
            edge++;
            *total += edge->chi = *dxptr;
            dxptr++;
            edge->left = nodeptr;
            edge->right = nodeptr+1;
            edge++;
            nodeptr++;
        }
        initMSCRNode( nodeptr );
        nodeptr->index = (i<<16)|(src.cols-1);
        *total += edge->chi = *dyptr;
        dyptr++;
        edge->left = nodeptr-src.cols;
        edge->right = nodeptr;
        edge++;
        nodeptr++;
    }
    initMSCRNode( nodeptr );
    nodeptr->index = (src.rows-1)<<16;
    *total += edge->chi = *dxptr;
    dxptr++;
    edge->left = nodeptr;
    edge->right = nodeptr+1;
    edge++;
    *total += edge->chi = *dyptr;
    dyptr++;
    edge->left = nodeptr-src.cols;
    edge->right = nodeptr;
    edge++;
    nodeptr++;
    for ( int i = 1; i < src.cols-1; i++ )
    {
        initMSCRNode( nodeptr );
        nodeptr->index = ((src.rows-1)<<16)|i;
        *total += edge->chi = *dxptr;
        dxptr++;
        edge->left = nodeptr;
        edge->right = nodeptr+1;
        edge++;
        *total += edge->chi = *dyptr;
        dyptr++;
        edge->left = nodeptr-src.cols;
        edge->right = nodeptr;
        edge++;
        nodeptr++;
    }
    initMSCRNode( nodeptr );
    nodeptr->index = ((src.rows-1)<<16)|(src.cols-1);
    *total += edge->chi = *dyptr;
    edge->left = nodeptr-src.cols;
    edge->right = nodeptr;

    return Ne;
}

class LessThanEdge
{
public:
    bool operator()(const MSCREdge& a, const MSCREdge& b) const { return a.chi < b.chi; }
};

// to find the root of one region
static MSCRNode* findMSCR( MSCRNode* x )
{
    MSCRNode* prev = x;
    MSCRNode* next;
    for ( ; ; )
    {
        next = x->shortcut;
        x->shortcut = prev;
        if ( next == x ) break;
        prev= x;
        x = next;
    }
    MSCRNode* root = x;
    for ( ; ; )
    {
        prev = x->shortcut;
        x->shortcut = root;
        if ( prev == x ) break;
        x = prev;
    }
    return root;
}

// the stable mscr should be:
// bigger than minArea and smaller than maxArea
// differ from its ancestor more than minDiversity
static bool MSCRStableCheck( MSCRNode* x, const MSER_Impl::Params& params )
{
    if ( x->size <= params.minArea || x->size >= params.maxArea )
        return false;
    if ( x->gmsr == NULL )
        return true;
    double div = (double)(x->size-x->gmsr->size)/(double)x->size;
    return div > params.minDiversity;
}

static void
extractMSER_8uC3( const Mat& src,
                  vector<vector<Point> >& msers,
                  vector<Rect>& bboxvec,
                  const MSER_Impl::Params& params )
{
    bboxvec.clear();
    MSCRNode* map = (MSCRNode*)cvAlloc( src.cols*src.rows*sizeof(map[0]) );
    int Ne = src.cols*src.rows*2-src.cols-src.rows;
    MSCREdge* edge = (MSCREdge*)cvAlloc( Ne*sizeof(edge[0]) );
    TempMSCR* mscr = (TempMSCR*)cvAlloc( src.cols*src.rows*sizeof(mscr[0]) );
    double emean = 0;
    Mat dx( src.rows, src.cols-1, CV_64FC1 );
    Mat dy( src.rows-1, src.cols, CV_64FC1 );
    Ne = preprocessMSER_8uC3( map, edge, &emean, src, dx, dy, Ne, params.edgeBlurSize );
    emean = emean / (double)Ne;
    std::sort(edge, edge + Ne, LessThanEdge());
    MSCREdge* edge_ub = edge+Ne;
    MSCREdge* edgeptr = edge;
    TempMSCR* mscrptr = mscr;
    // the evolution process
    for ( int i = 0; i < params.maxEvolution; i++ )
    {
        double k = (double)i/(double)params.maxEvolution*(TABLE_SIZE-1);
        int ti = cvFloor(k);
        double reminder = k-ti;
        double thres = emean*(chitab3[ti]*(1-reminder)+chitab3[ti+1]*reminder);
        // to process all the edges in the list that chi < thres
        while ( edgeptr < edge_ub && edgeptr->chi < thres )
        {
            MSCRNode* lr = findMSCR( edgeptr->left );
            MSCRNode* rr = findMSCR( edgeptr->right );
            // get the region root (who is responsible)
            if ( lr != rr )
            {
                // rank idea take from: N-tree Disjoint-Set Forests for Maximally Stable Extremal Regions
                if ( rr->rank > lr->rank )
                {
                    MSCRNode* tmp;
                    CV_SWAP( lr, rr, tmp );
                } else if ( lr->rank == rr->rank ) {
                    // at the same rank, we will compare the size
                    if ( lr->size > rr->size )
                    {
                        MSCRNode* tmp;
                        CV_SWAP( lr, rr, tmp );
                    }
                    lr->rank++;
                }
                rr->shortcut = lr;
                lr->size += rr->size;
                // join rr to the end of list lr (lr is a endless double-linked list)
                lr->prev->next = rr;
                lr->prev = rr->prev;
                rr->prev->next = lr;
                rr->prev = lr;
                // area threshold force to reinitialize
                if ( lr->size > (lr->size-rr->size)*params.areaThreshold )
                {
                    lr->sizei = lr->size;
                    lr->reinit = i;
                    if ( lr->tmsr != NULL )
                    {
                        lr->tmsr->m = lr->dt-lr->di;
                        lr->tmsr = NULL;
                    }
                    lr->di = edgeptr->chi;
                    lr->s = 1e10;
                }
                lr->dt = edgeptr->chi;
                if ( i > lr->reinit )
                {
                    double s = (double)(lr->size-lr->sizei)/(lr->dt-lr->di);
                    if ( s < lr->s )
                    {
                        // skip the first one and check stablity
                        if ( i > lr->reinit+1 && MSCRStableCheck( lr, params ) )
                        {
                            if ( lr->tmsr == NULL )
                            {
                                lr->gmsr = lr->tmsr = mscrptr;
                                mscrptr++;
                            }
                            lr->tmsr->size = lr->size;
                            lr->tmsr->head = lr;
                            lr->tmsr->tail = lr->prev;
                            lr->tmsr->m = 0;
                        }
                        lr->s = s;
                    }
                }
            }
            edgeptr++;
        }
        if ( edgeptr >= edge_ub )
            break;
    }
    for ( TempMSCR* ptr = mscr; ptr < mscrptr; ptr++ )
        // to prune area with margin less than minMargin
        if ( ptr->m > params.minMargin )
        {
            MSCRNode* lpt = ptr->head;
            int xmin = INT_MAX, ymin = INT_MAX, xmax = INT_MIN, ymax = INT_MIN;
            msers.push_back(vector<Point>());
            vector<Point>& mser = msers.back();

            for ( int i = 0; i < ptr->size; i++ )
            {
                Point pt;
                pt.x = (lpt->index)&0xffff;
                pt.y = (lpt->index)>>16;
                xmin = std::min(xmin, pt.x);
                xmax = std::max(xmax, pt.x);
                ymin = std::min(ymin, pt.y);
                ymax = std::max(ymax, pt.y);

                lpt = lpt->next;
                mser.push_back(pt);
            }
            bboxvec.push_back(Rect(xmin, ymin, xmax - xmin + 1, ymax - ymin + 1));
        }
    cvFree( &mscr );
    cvFree( &edge );
    cvFree( &map );
}

void MSER_Impl::detectRegions( InputArray _src, vector<vector<Point> >& msers, vector<Rect>& bboxes )
{
    Mat src = _src.getMat();
    size_t npix = src.total();

    msers.clear();
    bboxes.clear();

    if( npix == 0 )
        return;

    Size size = src.size();

    if( src.type() == CV_8U )
    {
        int level_size[256];
        if( !src.isContinuous() )
        {
            src.copyTo(tempsrc);
            src = tempsrc;
        }

        // darker to brighter (MSER+)
        preprocess1( src, level_size );
        if( !params.pass2Only )
            pass( src, msers, bboxes, size, level_size, 0 );
        // brighter to darker (MSER-)
        preprocess2( src, level_size );
        pass( src, msers, bboxes, size, level_size, 255 );
    }
    else
    {
        CV_Assert( src.type() == CV_8UC3 || src.type() == CV_8UC4 );
        extractMSER_8uC3( src, msers, bboxes, params );
    }
}

void MSER_Impl::detect( InputArray _image, vector<KeyPoint>& keypoints, InputArray _mask )
{
    vector<Rect> bboxes;
    vector<vector<Point> > msers;
    Mat mask = _mask.getMat();

    detectRegions(_image, msers, bboxes);
    int i, ncomps = (int)msers.size();

    keypoints.clear();
    for( i = 0; i < ncomps; i++ )
    {
        Rect r = bboxes[i];
        // TODO check transformation from MSER region to KeyPoint
        RotatedRect rect = fitEllipse(Mat(msers[i]));
        float diam = std::sqrt(rect.size.height*rect.size.width);

        if( diam > std::numeric_limits<float>::epsilon() && r.contains(rect.center) &&
            (mask.empty() || mask.at<uchar>(cvRound(rect.center.y), cvRound(rect.center.x)) != 0) )
            keypoints.push_back( KeyPoint(rect.center, diam) );
    }
}

Ptr<MSER> MSER::create( int _delta, int _min_area, int _max_area,
      double _max_variation, double _min_diversity,
      int _max_evolution, double _area_threshold,
      double _min_margin, int _edge_blur_size )
{
    return makePtr<MSER_Impl>(
        MSER_Impl::Params(_delta, _min_area, _max_area,
                          _max_variation, _min_diversity,
                          _max_evolution, _area_threshold,
                          _min_margin, _edge_blur_size));
}

}
/* [<][>][^][v][top][bottom][index][help] */
root/modules/features2d/src/mser.cpp

DEFINITIONS
