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Add demo code for cv::reduce, cv::merge and cv::split.

samples/cpp/tutorial_code/snippets/core_merge.cpp

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+/**
+ * @file core_merge.cpp
+ * @brief It demonstrates the usage of cv::merge.
+ *
+ * It shows how to merge 3 single channel matrices into a 3-channel matrix.
+ *
+ * @author KUANG Fangjun
+ * @date August 2017
+ */
+
+#include <iostream>
+#include <opencv2/core.hpp>
+
+using namespace std;
+using namespace cv;
+
+int main()
+{
+    //! [example]
+    Mat m1 = (Mat_<uchar>(2,2) << 1,4,7,10);
+    Mat m2 = (Mat_<uchar>(2,2) << 2,5,8,11);
+    Mat m3 = (Mat_<uchar>(2,2) << 3,6,9,12);
+
+    Mat channels[3] = {m1, m2, m3};
+    Mat m;
+    merge(channels, 3, m);
+    /*
+    m =
+    [  1,   2,   3,   4,   5,   6;
+       7,   8,   9,  10,  11,  12]
+    m.channels() = 3
+    */
+    //! [example]
+
+    return 0;
+}

samples/cpp/tutorial_code/snippets/core_reduce.cpp

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+/**
+ * @file core_reduce.cpp
+ * @brief It demonstrates the usage of cv::reduce .
+ *
+ * It shows how to compute the row sum, column sum, row average,
+ * column average, row minimum, column minimum, row maximum
+ * and column maximum of a cv::Mat.
+ *
+ * @author KUANG Fangjun
+ * @date August 2017
+ */
+
+#include <iostream>
+#include <opencv2/core.hpp>
+
+using namespace std;
+using namespace cv;
+
+int main()
+{
+    {
+        //! [example]
+        Mat m = (Mat_<uchar>(3,2) << 1,2,3,4,5,6);
+        Mat col_sum, row_sum;
+
+        reduce(m, col_sum, 0, CV_REDUCE_SUM, CV_32F);
+        reduce(m, row_sum, 1, CV_REDUCE_SUM, CV_32F);
+        /*
+        m =
+        [  1,   2;
+           3,   4;
+           5,   6]
+        col_sum =
+        [9, 12]
+        row_sum =
+        [3;
+         7;
+         11]
+         */
+        //! [example]
+
+        Mat col_average, row_average, col_min, col_max, row_min, row_max;
+        reduce(m, col_average, 0, CV_REDUCE_AVG, CV_32F);
+        cout << "col_average =\n" << col_average << endl;
+
+        reduce(m, row_average, 1, CV_REDUCE_AVG, CV_32F);
+        cout << "row_average =\n" << row_average << endl;
+
+        reduce(m, col_min, 0, CV_REDUCE_MIN, CV_8U);
+        cout << "col_min =\n" << col_min << endl;
+
+        reduce(m, row_min, 1, CV_REDUCE_MIN, CV_8U);
+        cout << "row_min =\n" << row_min << endl;
+
+        reduce(m, col_max, 0, CV_REDUCE_MAX, CV_8U);
+        cout << "col_max =\n" << col_max << endl;
+
+        reduce(m, row_max, 1, CV_REDUCE_MAX, CV_8U);
+        cout << "row_max =\n" << row_max << endl;
+
+        /*
+        col_average =
+        [3, 4]
+        row_average =
+        [1.5;
+         3.5;
+         5.5]
+        col_min =
+        [  1,   2]
+        row_min =
+        [  1;
+           3;
+           5]
+        col_max =
+        [  5,   6]
+        row_max =
+        [  2;
+           4;
+           6]
+        */
+    }
+
+    {
+        //! [example2]
+        // two channels
+        char d[] = {1,2,3,4,5,6};
+        Mat m(3, 1, CV_8UC2, d);
+        Mat col_sum_per_channel;
+        reduce(m, col_sum_per_channel, 0, CV_REDUCE_SUM, CV_32F);
+        /*
+        col_sum_per_channel =
+        [9, 12]
+        */
+        //! [example2]
+    }
+
+    return 0;
+}

samples/cpp/tutorial_code/snippets/core_split.cpp

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+/**
+ * @file core_split.cpp
+ * @brief It demonstrates the usage of cv::split .
+ *
+ * It shows how to split a 3-channel matrix into a 3 single channel matrices.
+ *
+ * @author KUANG Fangjun
+ * @date August 2017
+ */
+
+#include <iostream>
+#include <opencv2/core.hpp>
+
+using namespace std;
+using namespace cv;
+
+int main()
+{
+    //! [example]
+    char d[] = {1,2,3,4,5,6,7,8,9,10,11,12};
+    Mat m(2, 2, CV_8UC3, d);
+    Mat channels[3];
+    split(m, channels);
+
+    /*
+    channels[0] =
+    [  1,   4;
+       7,  10]
+    channels[1] =
+    [  2,   5;
+       8,  11]
+    channels[2] =
+    [  3,   6;
+       9,  12]
+    */
+    //! [example]
+
+    return 0;
+}