From 2f929376ec9046fb01b9eb271dead01e418ab29b Mon Sep 17 00:00:00 2001
From: Vitaly Tuzov <terfendail@mediana.jetos.com>
Date: Mon, 10 Sep 2018 20:05:45 +0300
Subject: [PATCH] Fixed meanStdDev() implementation for the case input matrix
 has more than 4 channels

---
 modules/core/src/mean.cpp         | 14 +++++++-------
 modules/core/test/test_arithm.cpp | 17 +++++++++++++++++
 2 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/modules/core/src/mean.cpp b/modules/core/src/mean.cpp
index 30959f3bf9..e17875c08b 100644
--- a/modules/core/src/mean.cpp
+++ b/modules/core/src/mean.cpp
@@ -306,14 +306,14 @@ static int sumsqr_(const T* src0, const uchar* mask, ST* sum, SQT* sqsum, int le
     if( !mask )
     {
         SumSqr_SIMD<T, ST, SQT> vop;
-        int i = vop(src0, mask, sum, sqsum, len, cn), k = cn % 4;
-        src += i * cn;
+        int x = vop(src0, mask, sum, sqsum, len, cn), k = cn % 4;
+        src = src0 + x * cn;
 
         if( k == 1 )
         {
             ST s0 = sum[0];
             SQT sq0 = sqsum[0];
-            for( ; i < len; i++, src += cn )
+            for(int i = x; i < len; i++, src += cn )
             {
                 T v = src[0];
                 s0 += v; sq0 += (SQT)v*v;
@@ -325,7 +325,7 @@ static int sumsqr_(const T* src0, const uchar* mask, ST* sum, SQT* sqsum, int le
         {
             ST s0 = sum[0], s1 = sum[1];
             SQT sq0 = sqsum[0], sq1 = sqsum[1];
-            for( ; i < len; i++, src += cn )
+            for(int i = x; i < len; i++, src += cn )
             {
                 T v0 = src[0], v1 = src[1];
                 s0 += v0; sq0 += (SQT)v0*v0;
@@ -338,7 +338,7 @@ static int sumsqr_(const T* src0, const uchar* mask, ST* sum, SQT* sqsum, int le
         {
             ST s0 = sum[0], s1 = sum[1], s2 = sum[2];
             SQT sq0 = sqsum[0], sq1 = sqsum[1], sq2 = sqsum[2];
-            for( ; i < len; i++, src += cn )
+            for(int i = x; i < len; i++, src += cn )
             {
                 T v0 = src[0], v1 = src[1], v2 = src[2];
                 s0 += v0; sq0 += (SQT)v0*v0;
@@ -351,10 +351,10 @@ static int sumsqr_(const T* src0, const uchar* mask, ST* sum, SQT* sqsum, int le
 
         for( ; k < cn; k += 4 )
         {
-            src = src0 + k;
+            src = src0 + x * cn + k;
             ST s0 = sum[k], s1 = sum[k+1], s2 = sum[k+2], s3 = sum[k+3];
             SQT sq0 = sqsum[k], sq1 = sqsum[k+1], sq2 = sqsum[k+2], sq3 = sqsum[k+3];
-            for( ; i < len; i++, src += cn )
+            for(int i = x; i < len; i++, src += cn )
             {
                 T v0, v1;
                 v0 = src[0], v1 = src[1];
diff --git a/modules/core/test/test_arithm.cpp b/modules/core/test/test_arithm.cpp
index 049c86dd0d..8b84436140 100644
--- a/modules/core/test/test_arithm.cpp
+++ b/modules/core/test/test_arithm.cpp
@@ -2184,4 +2184,21 @@ TEST(Core_ConvertTo, regression_12121)
     }
 }
 
+TEST(Core_MeanStdDev, regression_multichannel)
+{
+    {
+        uchar buf[] = { 1, 2, 3, 4, 5, 6, 7, 8,
+                        3, 4, 5, 6, 7, 8, 9, 10 };
+        double ref_buf[] = { 2., 3., 4., 5., 6., 7., 8., 9.,
+                             1., 1., 1., 1., 1., 1., 1., 1. };
+        Mat src(1, 2, CV_MAKETYPE(CV_8U, 8), buf);
+        Mat ref_m(8, 1, CV_64FC1, ref_buf);
+        Mat ref_sd(8, 1, CV_64FC1, ref_buf + 8);
+        Mat dst_m, dst_sd;
+        meanStdDev(src, dst_m, dst_sd);
+        EXPECT_EQ(0, cv::norm(dst_m, ref_m, NORM_L1));
+        EXPECT_EQ(0, cv::norm(dst_sd, ref_sd, NORM_L1));
+    }
+}
+
 }} // namespace