From 52535b356c2e14a572086ee2554e9f41156abdb7 Mon Sep 17 00:00:00 2001
From: Andrew Senin <andrew.senin@itseez.com>
Date: Thu, 29 Jan 2015 21:29:57 +0400
Subject: [PATCH] Fix for assert in compute when subimage is used (see issue
 #4149)

---
 modules/objdetect/src/hog.cpp | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/modules/objdetect/src/hog.cpp b/modules/objdetect/src/hog.cpp
index c078c2deba..32a6a21b92 100644
--- a/modules/objdetect/src/hog.cpp
+++ b/modules/objdetect/src/hog.cpp
@@ -301,8 +301,10 @@ void HOGDescriptor::computeGradient(const Mat& img, Mat& grad, Mat& qangle,
     for( y = 0; y < gradsize.height; y++ )
     {
         const uchar* imgPtr  = img.ptr(ymap[y]);
-        const uchar* prevPtr = img.ptr(ymap[y-1]);
-        const uchar* nextPtr = img.ptr(ymap[y+1]);
+        //In case subimage is used ptr() generates an assert for next and prev rows
+        //(see http://code.opencv.org/issues/4149)
+        const uchar* prevPtr = img.data + img.step*ymap[y-1];
+        const uchar* nextPtr = img.data + img.step*ymap[y+1];
 
         float* gradPtr = grad.ptr<float>(y);
         uchar* qanglePtr = qangle.ptr(y);