ximgproc: fix weightedMedianFilter crash on zero mask

modules/ximgproc/src/weighted_median_filter.cpp

@@ -493,7 +493,7 @@ Mat filterCore(Mat &I, Mat &F, float **wMap, int r=20, int nF=256, int nI=256, M
             // Move cut-point to the left
             if(balanceWeight >= 0)
             {
-                for(;balanceWeight >= 0 && curMedianVal; curMedianVal--)
+                for(;balanceWeight >= 0 && curMedianVal > 0; curMedianVal--)
                 {
                     float curWeight = 0;
                     int *nextHist = H[curMedianVal];
@@ -539,8 +539,13 @@ Mat filterCore(Mat &I, Mat &F, float **wMap, int r=20, int nF=256, int nI=256, M
             }
 
             // Weighted median is found and written to the output image
-            if(balanceWeight<0)outImg.ptr<int>(y,x)[0] = curMedianVal+1;
-            else outImg.ptr<int>(y,x)[0] = curMedianVal;
+            if(curMedianVal != -1)
+            {
+                if(balanceWeight < 0)
+                    outImg.ptr<int>(y,x)[0] = curMedianVal+1;
+                else
+                    outImg.ptr<int>(y,x)[0] = curMedianVal;
+            }
 
             // Update joint-histogram and BCB when local window is shifted.
             int fval,gval,*curHist;

modules/ximgproc/test/test_weighted_median_filter.cpp

@@ -102,6 +102,16 @@ TEST(WeightedMedianFilterTest, ReferenceAccuracy)
     EXPECT_LE(cvtest::norm(res, ref, NORM_L2), totalMaxError);
 }
 
+TEST(WeightedMedianFilterTest, mask_zeros_no_crash)
+{
+    Mat img = imread(getDataDir() + "cv/ximgproc/sources/01.png");
+    Mat mask = Mat::zeros(img.size(), CV_8U);
+    Mat filtered;
+    weightedMedianFilter(img, img, filtered, 3, 20, WMF_EXP, mask);
+
+    EXPECT_EQ(cv::norm(img, filtered, NORM_INF), 0.0);
+}
+
 INSTANTIATE_TEST_CASE_P(TypicalSET, WeightedMedianFilterTest, Combine(Values(szODD, szQVGA),  Values(WMF_EXP, WMF_IV2, WMF_OFF)));
 
 }