From c9f51d5eed07dbfe803c12a6b97f86bf662f2b21 Mon Sep 17 00:00:00 2001
From: Firat Kalaycilar <fkalaycilar@gmail.com>
Date: Fri, 21 Mar 2014 09:44:11 +0200
Subject: [PATCH 1/2] modified BackgroundSubtractorMOG2::getBackgroundImage so
 that it can now work with gray-level images.

---
 modules/video/src/bgfg_gaussmix2.cpp | 53 +++++++++++++---------------
 1 file changed, 24 insertions(+), 29 deletions(-)

diff --git a/modules/video/src/bgfg_gaussmix2.cpp b/modules/video/src/bgfg_gaussmix2.cpp
index b14bc8e1e..ddc8e64bd 100644
--- a/modules/video/src/bgfg_gaussmix2.cpp
+++ b/modules/video/src/bgfg_gaussmix2.cpp
@@ -577,54 +577,49 @@ void BackgroundSubtractorMOG2::operator()(InputArray _image, OutputArray _fgmask
 void BackgroundSubtractorMOG2::getBackgroundImage(OutputArray backgroundImage) const
 {
     int nchannels = CV_MAT_CN(frameType);
-    CV_Assert( nchannels == 3 );
-    Mat meanBackground(frameSize, CV_8UC3, Scalar::all(0));
-
+    CV_Assert(nchannels == 1 || nchannels == 3);
+    Mat meanBackground(frameSize, CV_MAKETYPE(CV_8U, nchannels), Scalar::all(0));
     int firstGaussianIdx = 0;
     const GMM* gmm = (GMM*)bgmodel.data;
-    const Vec3f* mean = reinterpret_cast<const Vec3f*>(gmm + frameSize.width*frameSize.height*nmixtures);
+    const float* mean = reinterpret_cast<const float*>(gmm + frameSize.width*frameSize.height*nmixtures);
     for(int row=0; row<meanBackground.rows; row++)
     {
         for(int col=0; col<meanBackground.cols; col++)
         {
             int nmodes = bgmodelUsedModes.at<uchar>(row, col);
-            Vec3f meanVal;
+            std::vector<float> meanVal(nchannels, 0.f);
             float totalWeight = 0.f;
             for(int gaussianIdx = firstGaussianIdx; gaussianIdx < firstGaussianIdx + nmodes; gaussianIdx++)
             {
                 GMM gaussian = gmm[gaussianIdx];
-                meanVal += gaussian.weight * mean[gaussianIdx];
+                size_t meanPosition = gaussianIdx*nchannels;
+                for(int chn = 0; chn < nchannels; chn++)
+                {
+                    meanVal[chn] += gaussian.weight * mean[meanPosition + chn];
+                }
                 totalWeight += gaussian.weight;
 
                 if(totalWeight > backgroundRatio)
                     break;
             }
-
-            meanVal *= (1.f / totalWeight);
-            meanBackground.at<Vec3b>(row, col) = Vec3b(meanVal);
+            float invWeight = 1.f/totalWeight;
+            for(int chn = 0; chn < nchannels; chn++)
+            {
+                meanVal[chn] *= invWeight;
+            }
+            switch(nchannels)
+            {
+            case 1:
+                meanBackground.at<uchar>(row, col) = (uchar)meanVal[0];
+                break;
+            case 3:
+                meanBackground.at<Vec3b>(row, col) = Vec3b(*reinterpret_cast<Vec3f*>(&meanVal[0]));
+                break;
+            }
             firstGaussianIdx += nmixtures;
         }
     }
-
-    switch(CV_MAT_CN(frameType))
-    {
-    case 1:
-    {
-        vector<Mat> channels;
-        split(meanBackground, channels);
-        channels[0].copyTo(backgroundImage);
-        break;
-    }
-
-    case 3:
-    {
-        meanBackground.copyTo(backgroundImage);
-        break;
-    }
-
-    default:
-        CV_Error(CV_StsUnsupportedFormat, "");
-    }
+    meanBackground.copyTo(backgroundImage);
 }
 
 }

From 990295644e4260656787172f959a676bdc0a1066 Mon Sep 17 00:00:00 2001
From: Firat Kalaycilar <fkalaycilar@gmail.com>
Date: Tue, 8 Apr 2014 16:10:32 +0300
Subject: [PATCH 2/2] made a performance improvement. changed the way the mean
 value for each pixel is assigned in the output image.

---
 modules/video/src/bgfg_gaussmix2.cpp | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/modules/video/src/bgfg_gaussmix2.cpp b/modules/video/src/bgfg_gaussmix2.cpp
index ddc8e64bd..9700dfebd 100644
--- a/modules/video/src/bgfg_gaussmix2.cpp
+++ b/modules/video/src/bgfg_gaussmix2.cpp
@@ -582,12 +582,12 @@ void BackgroundSubtractorMOG2::getBackgroundImage(OutputArray backgroundImage) c
     int firstGaussianIdx = 0;
     const GMM* gmm = (GMM*)bgmodel.data;
     const float* mean = reinterpret_cast<const float*>(gmm + frameSize.width*frameSize.height*nmixtures);
+    std::vector<float> meanVal(nchannels, 0.f);
     for(int row=0; row<meanBackground.rows; row++)
     {
         for(int col=0; col<meanBackground.cols; col++)
         {
             int nmodes = bgmodelUsedModes.at<uchar>(row, col);
-            std::vector<float> meanVal(nchannels, 0.f);
             float totalWeight = 0.f;
             for(int gaussianIdx = firstGaussianIdx; gaussianIdx < firstGaussianIdx + nmodes; gaussianIdx++)
             {
@@ -603,17 +603,16 @@ void BackgroundSubtractorMOG2::getBackgroundImage(OutputArray backgroundImage) c
                     break;
             }
             float invWeight = 1.f/totalWeight;
-            for(int chn = 0; chn < nchannels; chn++)
-            {
-                meanVal[chn] *= invWeight;
-            }
             switch(nchannels)
             {
             case 1:
-                meanBackground.at<uchar>(row, col) = (uchar)meanVal[0];
+                meanBackground.at<uchar>(row, col) = (uchar)(meanVal[0] * invWeight);
+                meanVal[0] = 0.f;
                 break;
             case 3:
-                meanBackground.at<Vec3b>(row, col) = Vec3b(*reinterpret_cast<Vec3f*>(&meanVal[0]));
+                Vec3f& meanVec = *reinterpret_cast<Vec3f*>(&meanVal[0]);
+                meanBackground.at<Vec3b>(row, col) = Vec3b(meanVec * invWeight);
+                meanVec = 0.f;
                 break;
             }
             firstGaussianIdx += nmixtures;