added minEigThreshold parameter to calcOpticalFlowPyrLK to filter out bad points earlier.

modules/video/include/opencv2/video/tracking.hpp

@@ -318,12 +318,13 @@ enum { OPTFLOW_USE_INITIAL_FLOW=4, OPTFLOW_FARNEBACK_GAUSSIAN=256 };
 CV_EXPORTS_W void calcOpticalFlowPyrLK( InputArray prevImg, InputArray nextImg,
                            InputArray prevPts, CV_OUT InputOutputArray nextPts,
                            OutputArray status, OutputArray err,
-                           Size winSize=Size(15,15), int maxLevel=3,
+                           Size winSize=Size(21,21), int maxLevel=3,
                            TermCriteria criteria=TermCriteria(
                             TermCriteria::COUNT+TermCriteria::EPS,
                             30, 0.01),
                            double derivLambda=0.5,
-                           int flags=0 );
+                           int flags=0,
+                           double minEigThreshold=1e-4);
 
 //! computes dense optical flow using Farneback algorithm
 CV_EXPORTS_W void calcOpticalFlowFarneback( InputArray prev, InputArray next,

modules/video/src/lkpyramid.cpp

@@ -134,7 +134,7 @@ struct LKTrackerInvoker
                       const Point2f* _prevPts, Point2f* _nextPts,
                       uchar* _status, float* _err,
                       Size _winSize, TermCriteria _criteria,
-                      int _level, int _maxLevel, int _flags )
+                      int _level, int _maxLevel, int _flags, float _minEigThreshold )
     {
         prevImg = &_prevImg;
         prevDeriv = &_prevDeriv;
@@ -148,6 +148,7 @@ struct LKTrackerInvoker
         level = _level;
         maxLevel = _maxLevel;
         flags = _flags;
+        minEigThreshold = _minEigThreshold;
     }
     
     void operator()(const BlockedRange& range) const
@@ -308,11 +309,12 @@ struct LKTrackerInvoker
             
             float D = A11*A22 - A12*A12;
             float minEig = (A22 + A11 - std::sqrt((A11-A22)*(A11-A22) +
-                                                  4.f*A12*A12))/(2*winSize.width*winSize.height);
-            if( err )
+                            4.f*A12*A12))/(2*winSize.width*winSize.height);
+            
+            if( err && (flags & CV_LKFLOW_GET_MIN_EIGENVALS) != 0 )
                 err[ptidx] = (float)minEig;
             
-            if( D < FLT_EPSILON )
+            if( minEig < minEigThreshold || D < FLT_EPSILON )
             {
                 if( level == 0 && status )
                     status[ptidx] = false;
@@ -431,6 +433,46 @@ struct LKTrackerInvoker
                 }
                 prevDelta = delta;
             }
+            
+            if( status[ptidx] && err && level == 0 && (flags & CV_LKFLOW_GET_MIN_EIGENVALS) == 0 )
+            {
+                Point2f nextPt = nextPts[ptidx];
+                Point inextPt;
+                
+                inextPt.x = cvFloor(nextPt.x);
+                inextPt.y = cvFloor(nextPt.y);
+                
+                if( inextPt.x < -winSize.width || inextPt.x >= J.cols ||
+                    inextPt.y < -winSize.height || inextPt.y >= J.rows )
+                {
+                    if( status )
+                        status[ptidx] = false;
+                    continue;
+                }
+                
+                float a = nextPt.x - inextPt.x;
+                float b = nextPt.y - inextPt.y;
+                iw00 = cvRound((1.f - a)*(1.f - b)*(1 << W_BITS));
+                iw01 = cvRound(a*(1.f - b)*(1 << W_BITS));
+                iw10 = cvRound((1.f - a)*b*(1 << W_BITS));
+                iw11 = (1 << W_BITS) - iw00 - iw01 - iw10;
+                float errval = 0.f;
+                
+                for( y = 0; y < winSize.height; y++ )
+                {
+                    const uchar* Jptr = (const uchar*)J.data + (y + inextPt.y)*step + inextPt.x*cn;
+                    const deriv_type* Iptr = (const deriv_type*)(IWinBuf.data + y*IWinBuf.step);
+                    
+                    for( x = 0; x < winSize.width*cn; x++ )
+                    {
+                        int diff = CV_DESCALE(Jptr[x]*iw00 + Jptr[x+cn]*iw01 +
+                                              Jptr[x+step]*iw10 + Jptr[x+step+cn]*iw11,
+                                              W_BITS1-5) - Iptr[x];
+                        errval += std::abs((float)diff);
+                    }
+                }
+                err[ptidx] = errval * 1.f/(32*winSize.width*cn*winSize.height);
+            }
         }
     }
     
@@ -446,6 +488,7 @@ struct LKTrackerInvoker
     int level;
     int maxLevel;
     int flags;
+    float minEigThreshold;
 };
     
 }
@@ -456,7 +499,7 @@ void cv::calcOpticalFlowPyrLK( InputArray _prevImg, InputArray _nextImg,
                            Size winSize, int maxLevel,
                            TermCriteria criteria,
                            double derivLambda,
-                           int flags )
+                           int flags, double minEigThreshold )
 {
 #ifdef HAVE_TEGRA_OPTIMIZATION
     if (tegra::calcOpticalFlowPyrLK(_prevImg, _nextImg, _prevPts, _nextPts, _status, _err, winSize, maxLevel, criteria, derivLambda, flags))
@@ -570,7 +613,8 @@ void cv::calcOpticalFlowPyrLK( InputArray _prevImg, InputArray _nextImg,
         parallel_for(BlockedRange(0, npoints), LKTrackerInvoker(prevPyr[level], derivI,
                                                                 nextPyr[level], prevPts, nextPts,
                                                                 status, err,
-                                                                winSize, criteria, level, maxLevel, flags));
+                                                                winSize, criteria, level, maxLevel,
+                                                                flags, (float)minEigThreshold));
     }
 }
 

samples/cpp/lkdemo.cpp

@@ -39,7 +39,7 @@ int main( int argc, char** argv )
 {
     VideoCapture cap;
     TermCriteria termcrit(CV_TERMCRIT_ITER|CV_TERMCRIT_EPS,20,0.03);
-    Size winSize(10,10);
+    Size subPixWinSize(10,10), winSize(31,31);
     
     const int MAX_COUNT = 500;
     bool needToInit = false;
@@ -81,7 +81,7 @@ int main( int argc, char** argv )
         {
             // automatic initialization
             goodFeaturesToTrack(gray, points[1], MAX_COUNT, 0.01, 10, Mat(), 3, 0, 0.04);
-            cornerSubPix(gray, points[1], winSize, Size(-1,-1), termcrit);
+            cornerSubPix(gray, points[1], subPixWinSize, Size(-1,-1), termcrit);
             addRemovePt = false;
         }
         else if( !points[0].empty() )
@@ -91,7 +91,7 @@ int main( int argc, char** argv )
             if(prevGray.empty())
                 gray.copyTo(prevGray);
             calcOpticalFlowPyrLK(prevGray, gray, points[0], points[1], status, err, winSize,
-                                 3, termcrit, 0);
+                                 3, termcrit, 0, 0, 0.001);
             size_t i, k;
             for( i = k = 0; i < points[1].size(); i++ )
             {