Wrap reduceArgMin and reduceArgMax (#1524)

* Wrap reduceArgMin and reduceArgMax

(cherry picked from commit 01f9e24)

* Mark boolean P/Invoke argument with MarshalAs and adapt unit tests

* Fix unit test assertions

src/OpenCvSharp/Cv2/Cv2_core.cs

@@ -715,6 +715,56 @@ public static double PSNR(InputArray src1, InputArray src2, double r = 255.0)
         GC.KeepAlive(mask);
     }
 
+    /// <summary>
+    /// Finds indices of max elements along provided axis
+    /// </summary>
+    /// <param name="src">Input single-channel array</param>
+    /// <param name="dst">Output array of type CV_32SC1 with the same dimensionality as src,
+    /// except for axis being reduced - it should be set to 1.</param>
+    /// <param name="axis">Axis to reduce along</param>
+    /// <param name="lastIndex">Whether to get the index of first or last occurrence of max</param>
+    public static void ReduceArgMax(InputArray src, OutputArray dst, int axis, bool lastIndex = false)
+    {
+        if (src == null)
+            throw new ArgumentNullException(nameof(src));
+        if (dst == null)
+            throw new ArgumentNullException(nameof(dst));
+        src.ThrowIfDisposed();
+        dst.ThrowIfNotReady();
+
+        NativeMethods.HandleException(
+            NativeMethods.core_reduceArgMax(src.CvPtr, dst.CvPtr, axis, lastIndex));
+
+        dst.Fix();
+        GC.KeepAlive(src);
+        GC.KeepAlive(dst);
+    }
+
+    /// <summary>
+    /// Finds indices of min elements along provided axis
+    /// </summary>
+    /// <param name="src">Input single-channel array</param>
+    /// <param name="dst">Output array of type CV_32SC1 with the same dimensionality as src,
+    /// except for axis being reduced - it should be set to 1.</param>
+    /// <param name="axis">Axis to reduce along</param>
+    /// <param name="lastIndex">Whether to get the index of first or last occurrence of min</param>
+    public static void ReduceArgMin(InputArray src, OutputArray dst, int axis, bool lastIndex = false)
+    {
+        if (src == null)
+            throw new ArgumentNullException(nameof(src));
+        if (dst == null)
+            throw new ArgumentNullException(nameof(dst));
+        src.ThrowIfDisposed();
+        dst.ThrowIfNotReady();
+
+        NativeMethods.HandleException(
+            NativeMethods.core_reduceArgMin(src.CvPtr, dst.CvPtr, axis, lastIndex));
+
+        dst.Fix();
+        GC.KeepAlive(src);
+        GC.KeepAlive(dst);
+    }
+
     /// <summary>
     /// finds global minimum and maximum array elements and returns their values and their locations
     /// </summary>

src/OpenCvSharp/Internal/PInvoke/NativeMethods/core/NativeMethods_core.cs

@@ -167,6 +167,12 @@ static partial class NativeMethods
     public static extern ExceptionStatus core_normalize(IntPtr src, IntPtr dst, double alpha, double beta,
         int normType, int dtype, IntPtr mask);
 
+    [Pure, DllImport(DllExtern, CallingConvention = CallingConvention.Cdecl, ExactSpelling = true)]
+    public static extern ExceptionStatus core_reduceArgMax(IntPtr src, IntPtr dst, int axis, [MarshalAs(UnmanagedType.U1)] bool lastIndex);
+
+    [Pure, DllImport(DllExtern, CallingConvention = CallingConvention.Cdecl, ExactSpelling = true)]
+    public static extern ExceptionStatus core_reduceArgMin(IntPtr src, IntPtr dst, int axis, [MarshalAs(UnmanagedType.U1)] bool lastIndex);
+
     [Pure, DllImport(DllExtern, CallingConvention = CallingConvention.Cdecl, ExactSpelling = true)]
     public static extern ExceptionStatus core_minMaxLoc1(IntPtr src, out double minVal, out double maxVal);
     [Pure, DllImport(DllExtern, CallingConvention = CallingConvention.Cdecl, ExactSpelling = true)]

src/OpenCvSharpExtern/core.h

@@ -198,6 +198,20 @@ CVAPI(ExceptionStatus) core_normalize(
     END_WRAP
 }
 
+CVAPI(ExceptionStatus) core_reduceArgMax(cv::_InputArray* src, cv::_OutputArray* dst, int axis, bool lastIndex)
+{
+    BEGIN_WRAP
+    cv::reduceArgMax(*src, *dst, axis, lastIndex);
+    END_WRAP
+}
+
+CVAPI(ExceptionStatus) core_reduceArgMin(cv::_InputArray* src, cv::_OutputArray* dst, int axis, bool lastIndex)
+{
+    BEGIN_WRAP
+    cv::reduceArgMin(*src, *dst, axis, lastIndex);
+    END_WRAP
+}
+
 CVAPI(ExceptionStatus) core_minMaxLoc1(cv::_InputArray* src, double* minVal, double* maxVal)
 {
     BEGIN_WRAP

test/OpenCvSharp.Tests/core/CoreTest.cs

@@ -437,4 +437,36 @@ public void NormVecd()
         var norm = Cv2.Norm(vec, NormTypes.L1);
         Assert.Equal(3.3333, norm, 9);
     }
+
+    [Fact]
+    public void ReduceArgMax()
+    {
+        using var src = new Mat(2, 2, MatType.CV_8UC1, new byte[] { 1, 2, 1, 4 });
+        using var dst = new Mat();
+
+        Cv2.ReduceArgMax(src, dst, axis: 0, lastIndex: true);
+
+        Assert.Equal(MatType.CV_32SC1, dst.Type());
+        Assert.Equal(1, dst.Rows);
+        Assert.Equal(2, dst.Cols);
+
+        Assert.Equal(1, dst.At<int>(0, 0)); // max along 1st column [1; 1], taking the last occurence
+        Assert.Equal(1, dst.At<int>(0, 1)); // max along 2nd column [2; 4]
+    }
+
+    [Fact]
+    public void ReduceArgMin()
+    {
+        using var src = new Mat(2, 2, MatType.CV_8UC1, new byte[] { 2, 1, 4, 4 });
+        using var dst = new Mat();
+
+        Cv2.ReduceArgMin(src, dst, axis: 1, lastIndex: false);
+
+        Assert.Equal(MatType.CV_32SC1, dst.Type());
+        Assert.Equal(2, dst.Rows);
+        Assert.Equal(1, dst.Cols);
+
+        Assert.Equal(1, dst.At<int>(0, 0)); // min along 1st row [2, 1]
+        Assert.Equal(0, dst.At<int>(1, 0)); // min along 2nd row [4, 4], taking the first occurence
+    }
 }