Add diamond structuring element

modules/imgproc/include/opencv2/imgproc.hpp

@@ -235,8 +235,9 @@ enum MorphShapes {
     MORPH_RECT    = 0, //!< a rectangular structuring element:  \f[E_{ij}=1\f]
     MORPH_CROSS   = 1, //!< a cross-shaped structuring element:
                        //!< \f[E_{ij} = \begin{cases} 1 & \texttt{if } {i=\texttt{anchor.y } {or } {j=\texttt{anchor.x}}} \\0 & \texttt{otherwise} \end{cases}\f]
-    MORPH_ELLIPSE = 2 //!< an elliptic structuring element, that is, a filled ellipse inscribed
+    MORPH_ELLIPSE = 2, //!< an elliptic structuring element, that is, a filled ellipse inscribed
                       //!< into the rectangle Rect(0, 0, esize.width, esize.height)
+    MORPH_DIAMOND = 3  //!< a diamond structuring element defined by Manhattan distance
 };
 
 //! @} imgproc_filter

modules/imgproc/include/opencv2/imgproc/types_c.h

@@ -389,6 +389,7 @@ enum MorphShapes_c
     CV_SHAPE_RECT      =0,
     CV_SHAPE_CROSS     =1,
     CV_SHAPE_ELLIPSE   =2,
+    CV_SHAPE_DIAMOND   =3,
     CV_SHAPE_CUSTOM    =100 //!< custom structuring element
 };
 

modules/imgproc/src/morph.dispatch.cpp

@@ -138,7 +138,7 @@ Mat getStructuringElement(int shape, Size ksize, Point anchor)
     int r = 0, c = 0;
     double inv_r2 = 0;
 
-    CV_Assert( shape == MORPH_RECT || shape == MORPH_CROSS || shape == MORPH_ELLIPSE );
+    CV_Assert( shape == MORPH_RECT || shape == MORPH_CROSS || shape == MORPH_ELLIPSE || shape == MORPH_DIAMOND );
 
     anchor = normalizeAnchor(anchor, ksize);
 
@@ -151,6 +151,11 @@ Mat getStructuringElement(int shape, Size ksize, Point anchor)
         c = ksize.width/2;
         inv_r2 = r ? 1./((double)r*r) : 0;
     }
+    else if( shape == MORPH_DIAMOND )
+    {
+        r = ksize.height/2;
+        c = ksize.width/2;
+    }
 
     Mat elem(ksize, CV_8U);
 
@@ -163,6 +168,16 @@ Mat getStructuringElement(int shape, Size ksize, Point anchor)
             j2 = ksize.width;
         else if( shape == MORPH_CROSS )
             j1 = anchor.x, j2 = j1 + 1;
+        else if( shape == MORPH_DIAMOND )
+        {
+            int dy = std::abs(i - r);
+            if( dy <= r )
+            {
+                int dx = r - dy;
+                j1 = std::max( c - dx, 0 );
+                j2 = std::min( c + dx + 1, ksize.width );
+            }
+        }
         else
         {
             int dy = i - r;

modules/imgproc/test/test_structuring_element.cpp

@@ -0,0 +1,17 @@
+#include "test_precomp.hpp"
+
+namespace opencv_test { namespace {
+
+TEST(MorphShapes, getStructuringElementDiamond)
+{
+    cv::Mat element = cv::getStructuringElement(cv::MORPH_DIAMOND, cv::Size(5,5));
+    cv::Mat expected = (cv::Mat_<uchar>(5,5) <<
+        0,0,1,0,0,
+        0,1,1,1,0,
+        1,1,1,1,1,
+        0,1,1,1,0,
+        0,0,1,0,0);
+    EXPECT_EQ(0, cvtest::norm(element, expected, cv::NORM_INF));
+}
+
+}} // namespace